LEXIVA tablets may be taken with or without food.

Adults should take LEXIVA oral suspension without food. Pediatric patients should take LEXIVA oral suspension with food [see Clinical Pharmacology (12.3)]. If emesis occurs within 30 minutes after dosing, re-dosing of LEXIVA oral suspension should occur.

Higher-than-approved dose combinations of LEXIVA plus ritonavir are not recommended due to an increased risk of transaminase elevations [see Overdosage (10)].

When LEXIVA is used in combination with ritonavir, prescribers should consult the full prescribing information for ritonavir.

Therapy-Naive Adults

• LEXIVA 1,400 mg twice daily (without ritonavir).
• LEXIVA 1,400 mg once daily plus ritonavir 200 mg once daily.
• LEXIVA 1,400 mg once daily plus ritonavir 100 mg once daily.
  • Dosing of LEXIVA 1,400 mg once daily plus ritonavir 100 mg once daily is supported by pharmacokinetic data [see Clinical Pharmacology (12.3)].
• LEXIVA 700 mg twice daily plus ritonavir 100 mg twice daily.
  • Dosing of LEXIVA 700 mg twice daily plus ritonavir 100 mg twice daily is supported by pharmacokinetic and safety data [see Clinical Pharmacology (12.3)].

Protease Inhibitor-Experienced Adults

• LEXIVA 700 mg twice daily plus ritonavir 100 mg twice daily.

Pregnancy

• LEXIVA 700 mg twice daily plus ritonavir 100 mg twice daily.
  • Dosing of LEXIVA 700 mg twice daily plus ritonavir 100 mg twice daily should only be considered in pregnant patients who are already on a stable twice-daily regimen of LEXIVA/ritonavir 700 mg/100 mg prior to pregnancy and who are virologically suppressed (HIV-1 RNA less than 50 copies per mL). Lower exposures of amprenavir were observed during pregnancy; therefore, viral load should be monitored closely to ensure viral suppression is maintained [see Use in Specific Populations (8.1), Clinical Pharmacology ( 12.3 )]. Data regarding use of other regimens of LEXIVA (with or without ritonavir) in pregnancy are not available.

The recommended dosage of LEXIVA in patients aged at least 4 weeks to 18 years should be calculated based on body weight (kg) and should not exceed the recommended adult dose (Table 1).

Table 1. Twice-Daily Dosage Regimens by Weight for Protease Inhibitor-Naive Pediatric Patients (Aged 4 Weeks and Older) and for Protease Inhibitor-Experienced Pediatric Patients (Aged 6 Months and Older) Using LEXIVA Oral Suspension with Concurrent Ritonavir

a When dosing with ritonavir, do not exceed the adult dose of LEXIVA 700 mg/ritonavir 100 mg twice-daily dose.
Weight	Twice-Daily Dosage Regimen
<11 kg	LEXIVA 45 mg/kg plus ritonavir 7 mg/kga
11 kg - <15 kg	LEXIVA 30 mg/kg plus ritonavir 3 mg/kga
15 kg - <20 kg	LEXIVA 23 mg/kg plus ritonavir 3 mg/kga
≥20 kg	LEXIVA 18 mg/kg plus ritonavir 3 mg/kga

Alternatively, protease inhibitor-naive children aged 2 years and older can be administered LEXIVA (without ritonavir) 30 mg per kg twice daily.

LEXIVA should only be administered to infants born at 38 weeks’ gestation or greater and who have attained a postnatal age of 28 days.

For pediatric patients, pharmacokinetic and clinical data:

• do not support once-daily dosing of LEXIVA alone or in combination with ritonavir [see Clinical Studies (14.3)].
• do not support administration of LEXIVA alone or in combination with ritonavir for protease inhibitor‑experienced children younger than 6 months [see Clinical Pharmacology (12.3)].
• do not support twice-daily dosing of LEXIVA without ritonavir in pediatric patients younger than 2 years [see Clinical Pharmacology (12.3)].

Other Dosing Considerations

• When administered without ritonavir, the adult regimen of LEXIVA tablets 1,400 mg twice daily may be used for pediatric patients weighing at least 47 kg.
• When administered in combination with ritonavir, LEXIVA tablets may be used for pediatric patients weighing at least 39 kg; ritonavir capsules may be used for pediatric patients weighing at least 33 kg.

See Clinical Pharmacology (12.3).

Mild Hepatic Impairment (Child-Pugh Score Ranging from 5 to 6)

LEXIVA should be used with caution at a reduced dosage of 700 mg twice daily without ritonavir (therapy-naive) or 700 mg twice daily plus ritonavir 100 mg once daily (therapy-naive or protease inhibitor-experienced).

Moderate Hepatic Impairment (Child-Pugh Score Ranging from 7 to 9)

LEXIVA should be used with caution at a reduced dosage of 700 mg twice daily without ritonavir (therapy-naive) or 450 mg twice daily plus ritonavir 100 mg once daily (therapy-naive or protease inhibitor-experienced).

Severe Hepatic Impairment (Child-Pugh Score Ranging from 10 to 15)

LEXIVA should be used with caution at a reduced dosage of 350 mg twice daily without ritonavir (therapy-naive) or 300 mg twice daily plus ritonavir 100 mg once daily (therapy-naive or protease inhibitor-experienced).

There are no data to support dosing recommendations for pediatric patients with hepatic impairment.

Initiation of LEXIVA/ritonavir, a CYP3A inhibitor, in patients receiving medications metabolized by CYP3A, or initiation of medications metabolized by CYP3A in patients already receiving LEXIVA/ritonavir may increase plasma concentrations of medications metabolized by CYP3A. Initiation of medications that inhibit or induce CYP3A may increase or decrease concentrations of LEXIVA/ritonavir, respectively. These interactions may lead to:

• clinically significant adverse reactions, potentially leading to severe, life-threatening, or fatal events from greater exposures of concomitant medications.
• clinically significant adverse reactions from greater exposures of LEXIVA/ritonavir.
• loss of therapeutic effect of LEXIVA/ritonavir and possible development of resistance.

See Table 6 for steps to prevent or manage these possible and known significant drug interactions, including dosing recommendations [see Drug Interactions (7)]. Consider the potential for drug interactions prior to and during therapy with LEXIVA/ritonavir; review concomitant medications during therapy with LEXIVA/ritonavir, and monitor for the adverse reactions associated with the concomitant medications [see Contraindications (4), Drug Interactions (7)].

Severe and life-threatening skin reactions, including 1 case of Stevens-Johnson syndrome among 700 subjects treated with LEXIVA in clinical trials. Treatment with LEXIVA should be discontinued for severe or life-threatening rashes and for moderate rashes accompanied by systemic symptoms [see Adverse Reactions (6)].

LEXIVA should be used with caution in patients with a known sulfonamide allergy. Fosamprenavir contains a sulfonamide moiety. The potential for cross-sensitivity between drugs in the sulfonamide class and fosamprenavir is unknown. In a clinical trial of LEXIVA used as the sole protease inhibitor, rash occurred in 2 of 10 subjects (20%) with a history of sulfonamide allergy compared with 42 of 126 subjects (33%) with no history of sulfonamide allergy. In 2 clinical trials of LEXIVA plus low-dose ritonavir, rash occurred in 8 of 50 subjects (16%) with a history of sulfonamide allergy compared with 50 of 412 subjects (12%) with no history of sulfonamide allergy.

Use of LEXIVA with ritonavir at higher-than-recommended dosages may result in transaminase elevations and should not be used [see Dosage and Administration (2), Overdosage (10)]. Patients with underlying hepatitis B or C or marked elevations in transaminases prior to treatment may be at increased risk for developing or worsening of transaminase elevations. Appropriate laboratory testing should be conducted prior to initiating therapy with LEXIVA and patients should be monitored closely during treatment.

New onset diabetes mellitus, exacerbation of pre-existing diabetes mellitus, and hyperglycemia have been reported during postmarketing surveillance in HIV-1–infected patients receiving protease inhibitor therapy. Some patients required either initiation or dose adjustments of insulin or oral hypoglycemic agents for treatment of these events. In some cases, diabetic ketoacidosis has occurred. In those patients who discontinued protease inhibitor therapy, hyperglycemia persisted in some cases. Because these events have been reported voluntarily during clinical practice, estimates of frequency cannot be made and causal relationships between protease inhibitor therapy and these events have not been established.

Immune reconstitution syndrome has been reported in patients treated with combination antiretroviral therapy, including LEXIVA. During the initial phase of combination antiretroviral treatment, patients whose immune systems respond may develop an inflammatory response to indolent or residual opportunistic infections (such as Mycobacterium avium infection, cytomegalovirus, Pneumocystis jirovecii pneumonia [PCP], or tuberculosis), which may necessitate further evaluation and treatment.

Autoimmune disorders (such as Graves’ disease, polymyositis, and Guillain-Barré syndrome) have also been reported to occur in the setting of immune reconstitution; however, the time to onset is more variable, and can occur many months after initiation of treatment.

Increase of body fat has been observed in patients receiving protease inhibitors, including LEXIVA. The mechanism and long-term consequences of these events are currently unknown. A causal relationship has not been established.

Treatment with LEXIVA plus ritonavir has resulted in increases in the concentration of triglycerides and cholesterol [see Adverse Reactions (6)]. Triglyceride and cholesterol testing should be performed prior to initiating therapy with LEXIVA and at periodic intervals during therapy. Lipid disorders should be managed as clinically appropriate [see Drug Interactions (7)].

Acute hemolytic anemia has been reported in a patient treated with amprenavir.

There have been reports of spontaneous bleeding in patients with hemophilia A and B treated with protease inhibitors. In some patients, additional factor VIII was required. In many of the reported cases, treatment with protease inhibitors was continued or restarted. A causal relationship between protease inhibitor therapy and these episodes has not been established.

Cases of nephrolithiasis were reported during postmarketing surveillance in HIV–1–infected patients receiving LEXIVA. Because these events were reported voluntarily during clinical practice, estimates of frequency cannot be made. If signs or symptoms of nephrolithiasis occur, temporary interruption or discontinuation of therapy may be considered.

Because the potential for HIV cross-resistance among protease inhibitors has not been fully explored, it is unknown what effect therapy with LEXIVA will have on the activity of subsequently administered protease inhibitors. LEXIVA has been studied in patients who have experienced treatment failure with protease inhibitors [see Clinical Studies (14.2)].

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared with rates in the clinical trials of another drug and may not reflect the rates observed in clinical practice.

Adult Trials

The data for the 3 active-controlled clinical trials described below reflect exposure of 700 HIV-1–infected subjects to LEXIVA tablets, including 599 subjects exposed to LEXIVA for greater than 24 weeks, and 409 subjects exposed for greater than 48 weeks. The population age ranged from 17 to 72 years. Of these subjects, 26% were female, 51% white, 31% black, 16% American Hispanic, and 70% were antiretroviral-naive. Sixty-one percent received LEXIVA 1,400 mg once daily plus ritonavir 200 mg once daily; 24% received LEXIVA 1,400 mg twice daily; and 15% received LEXIVA 700 mg twice daily plus ritonavir 100 mg twice daily.

Selected adverse reactions reported during the clinical efficacy trials of LEXIVA are shown in Tables 2 and 3. Each table presents adverse reactions of moderate or severe intensity in subjects treated with combination therapy for up to 48 weeks.

Table 2. Selected Moderate/Severe Clinical Adverse Reactions Reported in Greater than or Equal to 2% of Antiretroviral-Naive Adult Subjects

a All subjects also received abacavir and lamivudine twice daily.
Adverse Reaction	APV30001a		APV30002a
	LEXIVA 1,400 mg Twice Daily (n = 166)	Nelfinavir 1,250 mg Twice Daily (n = 83)	LEXIVA 1,400 mg and Ritonavir 200 mg Once Daily (n = 322)	Nelfinavir 1,250 mg Twice Daily (n = 327)
Gastrointestinal
Diarrhea	5%	18%	10%	18%
Nausea	7%	4%	7%	5%
Vomiting	2%	4%	6%	4%
Abdominal pain	1%	0%	2%	2%
Skin
Rash	8%	2%	3%	2%
General disorders
Fatigue	2%	1%	4%	2%
Nervous system
Headache	2%	4%	3%	3%

Table 3. Selected Moderate/Severe Clinical Adverse Reactions Reported in Greater than or Equal to 2% of Protease Inhibitor-Experienced Adult Subjects (Trial APV30003)

a All subjects also received 2 reverse transcriptase inhibitors.
Adverse Reaction	LEXIVA 700 mg and Ritonavir 100 mg Twice Dailya (n = 106)	Lopinavir 400 mg and Ritonavir 100 mg Twice Daily a (n = 103)
Gastrointestinal
Diarrhea	13%	11%
Nausea	3%	9%
Vomiting	3%	5%
Abdominal pain	<1%	2%
Skin
Rash	3%	0%
Nervous system
Headache	4%	2%

Skin rash (without regard to causality) occurred in approximately 19% of subjects treated with LEXIVA in the pivotal efficacy trials. Rashes were usually maculopapular and of mild or moderate intensity, some with pruritus. Rash had a median onset of 11 days after initiation of LEXIVA and had a median duration of 13 days. Skin rash led to discontinuation of LEXIVA in less than 1% of subjects. In some subjects with mild or moderate rash, dosing with LEXIVA was often continued without interruption; if interrupted, reintroduction of LEXIVA generally did not result in rash recurrence.

The percentages of subjects with Grade 3 or 4 laboratory abnormalities in the clinical efficacy trials of LEXIVA are presented in Tables 4 and 5.

Table 4. Grade 3/4 Laboratory Abnormalities Reported in Greater than or Equal to 2% of Antiretroviral-Naive Adult Subjects in Trials APV30001 and APV30002

a All subjects also received abacavir and lamivudine twice daily. b Fasting specimens. ULN = Upper limit of normal.
Laboratory Abnormality	APV30001a		APV30002a
	LEXIVA 1,400 mg Twice Daily (n = 166)	Nelfinavir 1,250 mg Twice Daily (n = 83)	LEXIVA 1,400 mg and Ritonavir 200 mg Once Daily (n = 322)	Nelfinavir 1,250 mg Twice Daily (n = 327)
ALT (>5 x ULN)	6%	5%	8%	8%
AST (>5 x ULN)	6%	6%	6%	7%
Serum lipase (>2 x ULN)	8%	4%	6%	4%
Triglyceridesb (>750 mg/dL)	0%	1%	6%	2%
Neutrophil count, absolute (<750 cells/mm3)	3%	6%	3%	4%

The incidence of Grade 3 or 4 hyperglycemia in antiretroviral-naive subjects who received LEXIVA in the pivotal trials was less than 1%.

Table 5. Grade 3/4 Laboratory Abnormalities Reported in Greater than or Equal to 2% of Protease Inhibitor-Experienced Adult Subjects in Trial APV30003

a All subjects also received 2 reverse transcriptase inhibitors. b Fasting specimens. c n = 100 for LEXIVA plus ritonavir, n = 98 for lopinavir plus ritonavir. ULN = Upper limit of normal.
Laboratory Abnormality	LEXIVA 700 mg and Ritonavir 100 mg Twice Daily a (n = 104)	Lopinavir 400 mg and Ritonavir 100 mg Twice Daily a (n = 103)
Triglyceridesb (>750 mg/dL)	11%c	6%c
Serum lipase (>2 x ULN)	5%	12%
ALT (>5 x ULN)	4%	4%
AST (>5 x ULN)	4%	2%
Glucose (>251 mg/dL)	2%c	2%c

Pediatric Trials

LEXIVA with and without ritonavir was studied in 237 HIV-1–infected pediatric subjects aged at least 4 weeks to 18 years in 3 open‑label trials; APV20002, APV20003, and APV29005 [see Clinical Studies (14.3)]. Vomiting and neutropenia occurred more frequently in pediatric subjects compared with adults. Other adverse events occurred with similar frequency in pediatric subjects compared with adults.

The frequency of vomiting among pediatric subjects receiving LEXIVA twice daily with ritonavir was 20% in subjects aged at least 4 weeks to younger than 2 years and 36% in subjects aged 2 to 18 years compared with 10% in adults. The frequency of vomiting among pediatric subjects receiving LEXIVA twice daily without ritonavir was 60% in subjects aged 2 to 5 years compared with 16% in adults.

The median duration of drug‑related vomiting episodes in APV29005 was 1 day (range: 1 to 3 days), in APV20003 was 16 days (range: 1 to 38 days), and in APV20002 was 9 days (range: 4 to 13 days). Vomiting was treatment limiting in 4 pediatric subjects across all 3 trials.

The incidence of Grade 3 or 4 neutropenia (neutrophils less than 750 cells per mm³) seen in pediatric subjects treated with LEXIVA with and without ritonavir was higher (15%) than the incidence seen in adult subjects (3%). Grade 3/4 neutropenia occurred in 10% (5 of 51) of subjects aged at least 4 weeks to younger than 2 years and 16% (28 of 170) of subjects aged 2 to 18 years.

The following adverse reactions have been identified during postapproval use of LEXIVA. Because these reactions are reported voluntarily from a population of unknown size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure. These reactions have been chosen for inclusion due to a combination of their seriousness, frequency of reporting, or potential causal connection to LEXIVA.

Cardiac Disorders

Myocardial infarction.

Metabolism and Nutrition Disorders

Hypercholesterolemia.

Nervous System Disorders

Oral paresthesia.

Skin and Subcutaneous Tissue Disorders

Angioedema.

Urogenital

Nephrolithiasis.

Amprenavir, the active metabolite of fosamprenavir, is an inhibitor of CYP3A4 metabolism and therefore should not be administered concurrently with medications with narrow therapeutic windows that are substrates of CYP3A4. Data also suggest that amprenavir induces CYP3A4.

Amprenavir is metabolized by CYP3A4. Coadministration of LEXIVA and drugs that induce CYP3A4, such as rifampin, may decrease amprenavir concentrations and reduce its therapeutic effect. Coadministration of LEXIVA and drugs that inhibit CYP3A4 may increase amprenavir concentrations and increase the incidence of adverse effects.

The potential for drug interactions with LEXIVA changes when LEXIVA is coadministered with the potent CYP3A4 inhibitor ritonavir. The magnitude of CYP3A4-mediated drug interactions (effect on amprenavir or effect on coadministered drug) may change when LEXIVA is coadministered with ritonavir. Because ritonavir is a CYP2D6 inhibitor, clinically significant interactions with drugs metabolized by CYP2D6 are possible when coadministered with LEXIVA plus ritonavir. Ritonavir also appears to induce CYP3A, CYP1A2, CYP2C9, CYP2C19, and CYP2B6, as well as other enzymes, including glucuronosyl transferase.

There are other agents that may result in serious and/or life-threatening drug interactions [see Contraindications (4)].

If LEXIVA is used in combination with ritonavir, see full prescribing information for ritonavir for additional information on drug interactions [see Contraindications (4), Clinical Pharmacology (12.3)].

Table 6 provides a listing of established or potentially clinically significant drug interactions. Information in the table applies to LEXIVA with or without ritonavir, unless otherwise indicated.

Table 6. Established and Other Potentially Significant Drug Interactions

a   See Clinical Pharmacology (12.3) Tables 10, 11, 12, or 13 for magnitude of interaction.
Concomitant Drug Class: Drug Name	Effect on Concentration of Amprenavir or Concomitant Drug	Clinical Comment
HCV/HIV-Antiviral Agents
HCV protease inhibitor: Boceprevir	LEXIVA: ↓Amprenavir (predicted) ↔ or ↓Boceprevir (predicted) LEXIVA/ritonavir: ↓Amprenavir (predicted) ↓Boceprevir (predicted)	Coadministration of LEXIVA or LEXIVA/ritonavir and boceprevir is not recommended.
HCV protease inhibitor: Simeprevir	LEXIVA: ↔Amprenavir (predicted) ↑ or ↓Simeprevir (predicted) LEXIVA/ritonavir: ↔Amprenavir (predicted) ↑Simeprevir (predicted)	Coadministration of LEXIVA or LEXIVA/ritonavir and simeprevir is not recommended.
HCV protease inhibitor: Paritaprevir (coformulated with ritonavir and ombitasvir and coadministered with dasabuvir)	LEXIVA: ↑Amprenavir (predicted) ↑ or ↔Paritaprevir (predicted) LEXIVA/ritonavir: ↑ or ↔Amprenavir (predicted) ↑Paritaprevir (predicted)	Appropriate doses of the combinations with respect to safety and efficacy have not been established. LEXIVA 1,400 mg once daily may be considered when coadministered with paritaprevir/ritonavir/ombitasvir/ dasabuvir. Coadministration of LEXIVA/ritonavir and paritaprevir/ritonavir/ombitasvir/ dasabuvir is not recommended.
Non-nucleoside reverse transcriptase inhibitor: Delavirdinea	LEXIVA: ↑Amprenavir ↓Delavirdine LEXIVA/ritonavir: ↑Amprenavir ↓Delavirdine	Coadministration is contraindicated as it may lead to loss of virologic response and possible resistance to delavirdine [see Contraindications (4)].
Non‑nucleoside reverse transcriptase inhibitor: Efavirenza	LEXIVA: ↓Amprenavir LEXIVA/ritonavir: ↓Amprenavir	Appropriate doses of the combinations with respect to safety and efficacy have not been established. An additional 100 mg/day (300 mg total) of ritonavir is recommended when efavirenz is administered with LEXIVA/ritonavir once daily. No change in the ritonavir dose is required when efavirenz is administered with LEXIVA plus ritonavir twice daily.
Non‑nucleoside reverse transcriptase inhibitor: Nevirapinea	LEXIVA: ↓Amprenavir ↑Nevirapine LEXIVA/ritonavir: ↓Amprenavir ↑Nevirapine	Coadministration of nevirapine and LEXIVA without ritonavir is not recommended. No dosage adjustment required when nevirapine is administered with LEXIVA/ritonavir twice daily. The combination of nevirapine administered with LEXIVA/ritonavir once‑daily regimen has not been studied.
HIV protease inhibitor: Atazanavira	LEXIVA: Interaction has not been evaluated. LEXIVA/ritonavir: ↓Atazanavir ↔Amprenavir	Appropriate doses of the combinations with respect to safety and efficacy have not been established.
HIV protease inhibitors: Indinavira, nelfinavira	LEXIVA: ↑Amprenavir Effect on indinavir and nelfinavir is not well established. LEXIVA/ritonavir: Interaction has not been evaluated.	Appropriate doses of the combinations with respect to safety and efficacy have not been established.
HIV protease inhibitors: Lopinavir/ritonavira	↓Amprenavir ↓Lopinavir	An increased rate of adverse events has been observed. Appropriate doses of the combinations with respect to safety and efficacy have not been established.
HIV protease inhibitor: Saquinavira	LEXIVA: ↓Amprenavir Effect on saquinavir is not well established. LEXIVA/ritonavir: Interaction has not been evaluated.	Appropriate doses of the combination with respect to safety and efficacy have not been established.
HIV integrase inhibitor: Raltegravira	LEXIVA: ↓Amprenavir ↓Raltegravir LEXIVA/ritonavir: ↓Amprenavir ↓Raltegravir	Appropriate doses of the combination with respect to safety and efficacy have not been established.
HIV integrase inhibitor: Dolutegravira	LEXIVA/ritonavir: ↓Dolutegravir	The recommended dose of dolutegravir is 50 mg twice daily when coadministered with LEXIVA/ritonavir. Use an alternative combination where possible in patients with known or suspected integrase inhibitor resistance.
HIV CCR5 co-receptor antagonist: Maraviroca	LEXIVA/ritonavir: ↓Amprenavir ↑Maraviroc	No dosage adjustment required for LEXIVA/ritonavir. The recommended dose of maraviroc is 150 mg twice daily when coadministered with LEXIVA/ritonavir. LEXIVA should be given with ritonavir when coadministered with maraviroc.
Other Agents
Alpha 1-adrenoreceptor antagonist: Alfuzosin	↑Alfuzosin	Coadministration is contraindicated due to potential hypotension [see Contraindications (4)].
Antacid: MAALOX TC	↓Amprenavir	Use with caution when administered at the same time. LEXIVA may be less effective due to decreased amprenavir plasma concentrations. Staggered coadministration of antacids and LEXIVA has not been evaluated.
Antiarrhythmics: Amiodarone, disopyramide, lidocaine (systemic), and quinidine	↑Antiarrhythmics	Therapeutic concentration monitoring, if available, is recommended for antiarrhythmics.
Antiarrhythmics: Flecainide, propafenone	↑Antiarrhythmics	Coadministration is contraindicated due to potential for serious and/or life‑threatening reactions such as cardiac arrhythmias if LEXIVA is co-prescribed with ritonavir [see Contraindications (4)].
Anticoagulant: Warfarin		Concentrations of warfarin may be affected. It is recommended that INR (international normalized ratio) be monitored.
Anticonvulsants: Carbamazepine, phenobarbital, phenytoin	LEXIVA: ↓Amprenavir	Use with caution. LEXIVA may be less effective due to decreased amprenavir plasma concentrations in patients taking these agents concomitantly.
Phenytoina	LEXIVA/ritonavir: ↑Amprenavir ↓Phenytoin	Plasma phenytoin concentrations should be monitored and phenytoin dose should be increased as appropriate. No change in LEXIVA/ritonavir dose is recommended.
Antidepressant: Paroxetine, trazodone	↓Paroxetine	Any paroxetine dose adjustment should be guided by clinical effect (tolerability and efficacy).
	↑Trazodone	Adverse events of nausea, dizziness, hypotension, and syncope have been observed following coadministration of trazodone and ritonavir. If trazodone is used with a CYP3A4 inhibitor such as LEXIVA, the combination should be used with caution and a lower dose of trazodone should be considered.
Antifungals: Ketoconazolea, itraconazole	↑Ketoconazole ↑Itraconazole	Increase monitoring for adverse events. LEXIVA: Dose reduction of ketoconazole or itraconazole may be needed for patients receiving more than 400 mg ketoconazole or itraconazole per day. LEXIVA/ritonavir: High doses of ketoconazole or itraconazole (greater than 200 mg/day) are not recommended.
Anti-gout: Colchicine	↑Colchicine	Patients with renal or hepatic impairment should not be given colchicine with LEXIVA/ritonavir. LEXIVA/ritonavir and coadministration of colchicine: Treatment of gout flares: 0.6 mg (1 tablet) x 1 dose, followed by 0.3 mg (half tablet) 1 hour later. Dose to be repeated no earlier than 3 days. Prophylaxis of gout flares: If the original regimen was 0.6 mg twice a day, the regimen should be adjusted to 0.3 mg once a day. If the original regimen was 0.6 mg once a day, the regimen should be adjusted to 0.3 mg once every other day. Treatment of familial Mediterranean fever (FMF): Maximum daily dose of 0.6 mg (may be given as 0.3 mg twice a day). LEXIVA and coadministration of colchicine: Treatment of gout flares: 1.2 mg (2 tablets) x 1 dose. Dose to be repeated no earlier than 3 days. Prophylaxis of gout flares: If the original regimen was 0.6 mg twice a day, the regimen should be adjusted to 0.3 mg twice a day or 0.6 mg once a day. If the original regimen was 0.6 mg once a day, the regimen should be adjusted to 0.3 mg once a day. Treatment of FMF: Maximum daily dose of 1.2 mg (may be given as 0.6 mg twice a day).
Antimycobacterial: Rifabutina	↑Rifabutin and rifabutin metabolite	A complete blood count should be performed weekly and as clinically indicated to monitor for neutropenia. LEXIVA: A dosage reduction of rifabutin by at least half the recommended dose is required. LEXIVA/ritonavir: Dosage reduction of rifabutin by at least 75% of the usual dose of 300 mg/day is recommended (a maximum dose of 150 mg every other day or 3 times per week).
Antimycobacterial: Rifampina	↓Amprenavir	Coadministration is contraindicated as it may lead to loss of virologic response and possible resistance to LEXIVA or to the class of protease inhibitors [see Contraindications (4)].
Antineoplastics: Dasatinib, nilotinib, ibrutinib, vinblastine, everolimus	↑Antineoplastics	LEXIVA or LEXIVA/ritonavir may increase plasma concentrations of antineoplastics metabolized by CYP3A, potentially increasing the risk of adverse events typically associated with these medications. In case of coadministration, please refer to relevant prescribing information for these medications.
Antipsychotics:
Lurasidone	↑Lurasidone	LEXIVA: If coadministration is necessary, reduce the lurasidone dose. Refer to the lurasidone prescribing information for concomitant use with moderate CYP3A4 inhibitors. LEXIVA/ritonavir: Use of lurasidone is contraindicated due to potential for serious and/or life-threatening reactions [see Contraindications (4)].
Pimozide	↑Pimozide	Coadministration is contraindicated due to potential for serious and/or life-threatening reactions such as cardiac arrhythmias [see Contraindications (4)].
Quetiapine	↑Quetiapine	LEXIVA/ritonavir: Initiation of LEXIVA with ritonavir in patients taking quetiapine: Consider alternative antiretroviral therapy to avoid increases in quetiapine drug exposures. If coadministration is necessary, reduce the quetiapine dose to 1/6 of the current dose and monitor for quetiapine-associated adverse reactions. Refer to the quetiapine prescribing information for recommendations on adverse reaction monitoring. Initiation of quetiapine in patients taking LEXIVA with ritonavir: Refer to the quetiapine prescribing information for initial dosing and titration of quetiapine.
Benzodiazepines: Alprazolam, clorazepate, diazepam, flurazepam	↑Benzodiazepines	Clinical significance is unknown. A decrease in benzodiazepine dose may be needed.
Calcium channel blockers: Diltiazem, felodipine, nifedipine, nicardipine, nimodipine, verapamil, amlodipine, nisoldipine, isradipine	↑Calcium channel blockers	Use with caution. Clinical monitoring of patients is recommended.
Corticosteroid: Dexamethasone	↓Amprenavir	Use with caution. LEXIVA may be less effective due to decreased amprenavir plasma concentrations.
Endothelin‑receptor antagonist: Bosentan	↑Bosentan	Coadministration of bosentan in patients on LEXIVA: In patients who have been receiving LEXIVA for at least 10 days, start bosentan at 62.5 mg once daily or every other day based upon individual tolerability. Coadministration of LEXIVA in patients on bosentan: Discontinue use of bosentan at least 36 hours prior to initiation of LEXIVA. After at least 10 days following the initiation of LEXIVA, resume bosentan at 62.5 mg once daily or every other day based upon individual tolerability.
Ergot derivatives: Dihydroergotamine, ergonovine, ergotamine, methylergonovine	↑Ergot derivatives	Coadministration is contraindicated due to potential for serious and/or life‑threatening reactions such as acute ergot toxicity characterized by peripheral vasospasm and ischemia of the extremities and other tissues [see Contraindications (4)].
GI motility agent: Cisapride	↑Cisapride	Coadministration is contraindicated due to potential for serious and/or life‑threatening reactions such as cardiac arrhythmias [see Contraindications (4)].
Herbal product: St. John’s wort (Hypericum perforatum)	↓Amprenavir	Coadministration is contraindicated as it may lead to loss of virologic response and possible resistance to LEXIVA or to the class of protease inhibitors [see Contraindications (4)].
Histamine H2-receptor antagonists: Cimetidine, famotidine, nizatidine, ranitidinea	LEXIVA: ↓Amprenavir LEXIVA/ritonavir: Interaction not evaluated	Use with caution. LEXIVA may be less effective due to decreased amprenavir plasma concentrations.
Immunosuppressants: Cyclosporine, tacrolimus, sirolimus	↑Immunosuppressants	Therapeutic concentration monitoring is recommended for immunosuppressant agents.
Inhaled beta‑agonist: Salmeterol	↑Salmeterol	Concurrent administration of salmeterol with LEXIVA is not recommended. The combination may result in increased risk of cardiovascular adverse events associated with salmeterol, including QT prolongation, palpitations, and sinus tachycardia.
Inhaled/nasal steroid: Fluticasone	LEXIVA: ↑Fluticasone LEXIVA/ritonavir: ↑Fluticasone	Use with caution. Consider alternatives to fluticasone, particularly for long‑term use. May result in significantly reduced serum cortisol concentrations. Systemic corticosteroid effects including Cushing’s syndrome and adrenal suppression have been reported during postmarketing use in patients receiving ritonavir and inhaled or intranasally administered fluticasone. Coadministration of fluticasone and LEXIVA/ritonavir is not recommended unless the potential benefit to the patient outweighs the risk of systemic corticosteroid side effects.
Lipid Modifying Agents: HMG-CoA reductase inhibitors:
Atorvastatina	↑Atorvastatin	Titrate atorvastatin dose carefully and use the lowest necessary dose; do not exceed atorvastatin 20 mg/day.
Lovastatin, simvastatin	↑Lovastatin ↑Simvastatin	Coadministration with lovastatin or simvastatin is contraindicated due to potential for serious reactions such as risk of myopathy including rhabdomyolysis [see Contraindications (4)].
Other lipid modifying agents:
Lomitapide	↑Lomitapide	Coadministration with lomitapide is contraindicated due to potential for markedly increased transaminases.
Narcotic analgesic: Methadone	↓Methadone	Data suggest that the interaction is not clinically relevant; however, patients should be monitored for opiate withdrawal symptoms.
Fentanyl	↑Fentanyl	Careful monitoring of therapeutic effects and adverse effects of fentanyl (including potentially fatal respiratory depression) is recommended.
Oral contraceptives: Ethinyl estradiol/ norethindronea	LEXIVA: ↓Amprenavir ↓Ethinyl estradiol LEXIVA/ritonavir: ↓Ethinyl estradiol	Alternative methods of non-hormonal contraception are recommended. May lead to loss of virologic response.a Increased risk of transaminase elevations. No data are available on the use of LEXIVA/ritonavir with other hormonal therapies, such as hormone replacement therapy (HRT) for postmenopausal women.
PDE5 inhibitors: Sildenafil, tadalafil, vardenafil	↑Sildenafil ↑Tadalafil ↑Vardenafil	May result in an increase in PDE5 inhibitor‑associated adverse events, including hypotension, syncope, visual disturbances, and priapism. Use of PDE5 inhibitors for pulmonary arterial hypertension (PAH): Use of sildenafil (REVATIO) is contraindicated when used for the treatment of PAH. A safe and effective dose has not been established when used with LEXIVA. There is increased potential for sildenafil-associated adverse events (which include visual disturbances, hypotension, prolonged erection, and syncope) [see Contraindications (4)]. The following dose adjustments are recommended for use of tadalafil (ADCIRCA® ) with LEXIVA: Coadministration of ADCIRCA in patients on LEXIVA: In patients receiving LEXIVA for at least one week, start ADCIRCA at 20 mg once daily. Increase to 40 mg once daily based upon individual tolerability. Coadministration of LEXIVA in patients on ADCIRCA: Avoid use of ADCIRCA during the initiation of LEXIVA. Stop ADCIRCA at least 24 hours prior to starting LEXIVA. After at least one week following the initiation of LEXIVA, resume ADCIRCA at 20 mg once daily. Increase to 40 mg once daily based upon individual tolerability. Use of PDE5 inhibitors for erectile dysfunction: LEXIVA: Sildenafil: 25 mg every 48 hours. Tadalafil: no more than 10 mg every 72 hours. Vardenafil: no more than 2.5 mg every 24 hours. LEXIVA/ritonavir: Sildenafil: 25 mg every 48 hours. Tadalafil: no more than 10 mg every 72 hours. Vardenafil: no more than 2.5 mg every 72 hours. Use with increased monitoring for adverse events.
Proton pump inhibitors: Esomeprazolea, lansoprazole, omeprazole, pantoprazole, rabeprazole	LEXIVA: ↔Amprenavir ↑Esomeprazole LEXIVA/ritonavir: ↔Amprenavir ↔Esomeprazole	Proton pump inhibitors can be administered at the same time as a dose of LEXIVA with no change in plasma amprenavir concentrations.
Sedative/hypnotics: Midazolam, triazolam	↑Midazolam ↑Triazolam	Coadministration is contraindicated due to potential for serious and/or life‑threatening reactions such as prolonged or increased sedation or respiratory depression [see Contraindications (4)].
Tricyclic antidepressants: Amitriptyline, imipramine	↑Tricyclics	Therapeutic concentration monitoring is recommended for tricyclic antidepressants.

Pregnancy Exposure Registry

There is a pregnancy exposure registry that monitors pregnancy outcomes in women exposed to LEXIVA during pregnancy. Healthcare providers are encouraged to register patients by calling the Antiretroviral Pregnancy Registry (APR) at 1-800-258-4263.

Risk Summary

Limited data are available for use of LEXIVA in pregnancy. LEXIVA 700 mg twice daily taken with ritonavir 100 mg twice daily should only be considered in pregnant patients who are already on a stable twice-daily regimen of LEXIVA/ritonavir 700 mg/100 mg prior to pregnancy, and who are virologically suppressed (HIV-1 RNA less than 50 copies per mL) (see Clinical Considerations and Data).

There are insufficient human data on the use of fosamprenavir during pregnancy to adequately assess a drug-associated risk for birth defects and miscarriage. Given the limited number of pregnancies exposed to fosamprenavir-based regimens, no conclusions can be drawn on the safety of fosamprenavir in pregnancy. The background risk for major birth defects and miscarriage for the indicated population is unknown. The background rate for major birth defects in a U.S. reference population of the Metropolitan Atlanta Congenital Defects Program (MACDP) is 2.7% (see Data). The estimated background rate of miscarriage in clinically recognized pregnancies in the U.S. general population is 15% to 20%.

In animal reproduction studies, no evidence of major adverse developmental outcomes was observed following oral administration of fosamprenavir. Systemic exposure to amprenavir (the active ingredient) was less than (rabbits) or up to 2 times (rats) those in humans at the maximum recommended human dose (MRHD) with or without ritonavir. In contrast, oral administration of amprenavir was associated with abortions in pregnant rabbits at doses that produced approximately one-twentieth the human exposure at the MRHD.

In the rat pre- and postnatal development study, toxicities to the offspring, including reduced survival and reproductive performance, were observed at maternal systemic exposures (AUC) to amprenavir that were approximately 2 times the exposure in humans at the MRHD of fosamprenavir alone or approximately the same as those seen in humans following administration of the MRHD of fosamprenavir in combination with ritonavir (see Data).

Clinical Considerations

Virologic Monitoring During Pregnancy and the Postpartum Period: Based on limited data on the use of LEXIVA during pregnancy, no dosage adjustments are required for pregnant patients who are already on a stable twice-daily regimen of LEXIVA 700 mg taken with ritonavir 100 mg prior to pregnancy, and who are virologically suppressed (HIV-1 RNA less than 50 copies per mL) [see Dosage and Administration (2.3), Clinical Pharmacology (12.3)]. In a clinical trial of 10 HIV-1–infected pregnant women treated with LEXIVA 700 mg taken with ritonavir 100 mg twice daily through postpartum, total amprenavir exposures were lower during pregnancy compared with the postpartum period. Therefore, viral load should be monitored closely to ensure viral suppression is maintained [see Data, Dosage and Administration (2.2), Clinical Pharmacology (12.3)]. Pregnancy data with other dosage regimens of LEXIVA (with or without ritonavir) are not available.

Data

Human Data: LEXIVA 700 mg taken with ritonavir 100 mg twice daily in combination with a background regimen was evaluated in a clinical trial of 10 HIV-1–infected pregnant women during the second and third trimesters and postpartum. Subjects initiated LEXIVA/ritonavir during pregnancy at a median of 19 weeks’ gestation; 4 had undetectable HIV-1 RNA viral load (less than 50 copies/mL) at the time of initiation. Amprenavir pharmacokinetics and placental transfer were studied during the second trimester (n = 6) or third trimester (n = 9) and postpartum (n = 9). Pregnancy outcomes were available for all 10 subjects, among which 1 twin pregnancy was included. Compared to the postpartum period, geometric mean amprenavir AUC was 35% lower in the second trimester and 25% lower in the third trimester. The amprenavir geometric mean ratio (95% CI) of fetal cord to maternal peripheral plasma concentration (n = 7) was 0.27 (0.24 to 0.30) [see Clinical Pharmacology (12.3)]. At delivery, 9 subjects had HIV-1 viral load less than 50 copies/mL, and 1 subject had a viral load of 111 copies/mL. All 11 infants born had test results that were negative for HIV-1 at the time of delivery and through 12 months postpartum. There were no new safety findings compared with the known safety profile of LEXIVA/ritonavir in HIV-1–infected adults.

Based on prospective reports to the APR of approximately 146 live births following exposure to fosamprenavir-containing regimens, there were 2 birth defects reported in 109 first trimester exposures and 2 birth defects reported in 36 second and third trimester exposures. The background rate for major birth defects is 2.7% in a U.S. reference population of the MACDP. Prospective reports from the APR of overall major birth defects in pregnancies exposed to fosamprenavir are compared with the U.S. background major birth defect rate. Methodological limitations of the APR include the use of the MACDP as the external comparator group. Limitations of using an external comparator include differences in methodology and populations as well as confounding due to the underlying disease.

Animal Data: Fosamprenavir was administered orally to pregnant rats (300, 820, or 2,240 mg per kg per day) and rabbits (74.8, 224.3, or 672.8 mg per kg per day) on Gestation Days 6 to 17 and Days 7 to 20, respectively. No major adverse effects on embryo-fetal development were observed at these dose levels, resulting in exposures (AUC_{0-24 h}) approximately 2 times (rats) and 0.8 times (rabbits) human exposures at the MRHD of fosamprenavir alone or 0.7 times (rats) and 0.3 times (rabbits) human exposures at the MRHD of fosamprenavir in combination with ritonavir. However, increased incidence of abortion was observed in rabbits administered a maternally toxic dose of fosamprenavir (672.8 mg per kg per day). In a study where amprenavir was administered orally to pregnant rabbits (25, 50, or 100 mg per kg per day) on Gestation Days 8 to 20, increased abortions and an increased incidence of minor skeletal variations (deficient ossification of the femur, humerus, and trochlea) were observed at doses that produced approximately one-twentieth the exposure seen at the MRHD.

In the rat pre- and postnatal development study, fosamprenavir was administered orally (300, 820, or 2,240 mg per kg per day) on Gestation Day 6 to Lactation/Postpartum Day 20. Fosamprenavir caused a reduction in pup survival and body weights. In surviving female offspring from the high-dose group, an increased time to successful mating, an increased length of gestation, a reduced number of uterine implantation sites per litter, and reduced gestational body weights were observed. Systemic exposure (AUC_{0-24 h}) to amprenavir in rats was approximately 2 times the exposures in humans at the MRHD of fosamprenavir alone or approximately the same as those seen in humans at the MRHD of fosamprenavir in combination with ritonavir.

Risk Summary

The Centers for Disease Control and Prevention recommends that HIV-1–infected mothers in the United States not breastfeed their infants to avoid risking postnatal transmission of HIV-1 infection.

There is no information available on the presence of amprenavir in human milk, the effects of the drug on the breastfed infant, or the effects of the drug on milk production. When administered to lactating rats, amprenavir was present in milk (see Data). Because of the potential for (1) HIV-1 transmission (in HIV-negative infants), (2) developing viral resistance (in HIV-positive infants), and (3) adverse reactions in a breastfed infant, instruct mothers not to breastfeed if they are receiving LEXIVA.

Data

Amprenavir was excreted into the milk of lactating rats following a single dose of amprenavir (100 mg per kg); a maximal milk concentration was achieved 2 hours post-administration at a milk concentration approximately 1.2 times that of maternal plasma concentrations.

Contraception

Use of LEXIVA may reduce the efficacy of combined hormonal contraceptives. Advise patients using combined hormonal contraceptives to use an effective alternative contraceptive method or an additional barrier method of contraception [see Drug Interactions (7.2)].

The safety, pharmacokinetic profile, and virologic and immunologic responses of LEXIVA with and without ritonavir were evaluated in protease inhibitor-naive and -experienced HIV-1–infected pediatric subjects aged at least 4 weeks to younger than 18 years and weighing at least 3 kg in 3 open-label trials [see Adverse Reactions (6.1), Clinical Pharmacology (12.3), Clinical Studies (14.3)].

Treatment with LEXIVA is not recommended in protease inhibitor-experienced pediatric patients younger than 6 months. The pharmacokinetics, safety, tolerability, and efficacy of LEXIVA in pediatric patients younger than 4 weeks have not been established [see Clinical Pharmacology (12.3)]. Available pharmacokinetic and clinical data do not support once-daily dosing of LEXIVA alone or in combination with ritonavir for any pediatrics or twice-daily dosing without ritonavir in pediatric patients younger than 2 years [see Clinical Pharmacology (12.3), Clinical Studies (14.3)]. See Dosage and Administration (2.3) for dosing recommendations for pediatric patients.

Clinical studies of LEXIVA did not include sufficient numbers of patients aged 65 and over to determine whether they respond differently from younger adults. In general, dose selection for an elderly patient should be cautious, reflecting the greater frequency of decreased hepatic, renal, or cardiac function and of concomitant disease or other drug therapy.

Amprenavir is principally metabolized by the liver; therefore, caution should be exercised when administering LEXIVA to patients with hepatic impairment because amprenavir concentrations may be increased [see Clinical Pharmacology (12.3)]. Patients with impaired hepatic function receiving LEXIVA with or without concurrent ritonavir require dose reduction [see Dosage and Administration (2.4)].

There are no data to support dosing recommendations for pediatric subjects with hepatic impairment.

Fosamprenavir is an HIV-1 antiretroviral agent [see Microbiology (12.4)].

The pharmacokinetic properties of amprenavir after administration of LEXIVA, with or without ritonavir, have been evaluated in both healthy adult volunteers and in HIV-1–infected subjects; no substantial differences in steady-state amprenavir concentrations were observed between the 2 populations.

The pharmacokinetic parameters of amprenavir after administration of LEXIVA (with and without concomitant ritonavir) are shown in Table 7.

Table 7. Geometric Mean (95% CI) Steady-State Plasma Amprenavir Pharmacokinetic Parameters in Adults

a Data shown are median (range). b Ctau is the concentration at the end of the dose interval. c HIV-infected adults. d AUC24 was calculated from AUC12 summary data x 2. e Healthy adults.
Regimen	Cmax (mcg/mL)	Tmax (hours)a	AUC24 (mcgh/mL)	Ctau b (mcg/mL)
LEXIVA 1,400 mg Twice Daily (n = 22)c	4.82 (4.06-5.72)	1.3 (0.8-4.0)	33.0d (27.6-39.2)	0.35 (0.27-0.46)
LEXIVA 1,400 mg Once Daily plus Ritonavir 200 mg Once Daily (n = 22)e	7.24 (6.32-8.28)	2.1 (0.8-5.0)	69.4 (59.7-80.8)	1.45 (1.16-1.81)
LEXIVA 1,400 mg Once Daily plus Ritonavir 100 mg Once Daily (n = 36)e	7.93 (7.25-8.68)	1.5 (0.75-5.0)	66.4 (61.1-72.1)	0.86 (0.74-1.01)
LEXIVA 700 mg Twice Daily plus Ritonavir 100 mg Twice Daily (n = 24)e	6.08 (5.38-6.86)	1.5 (0.75-5.0)	79.2d (69.0-90.6)	2.12 (1.77-2.54)

The mean plasma amprenavir concentrations of the dosing regimens over the dosing intervals are displayed in Figure 1.

Figure 1. Mean (±SD) Steady-State Plasma Amprenavir Concentrations and Mean EC₅₀ Values against HIV from Protease Inhibitor-Naive Subjects (in the Absence of Human Serum)

Absorption

After administration of a single dose of LEXIVA to HIV-1–infected subjects, the time to peak amprenavir concentration (T_max) occurred between 1.5 and 4 hours (median 2.5 hours). The absolute oral bioavailability of amprenavir after administration of LEXIVA in humans has not been established.

After administration of a single 1,400-mg dose in the fasted state, LEXIVA oral suspension (50 mg per mL) and LEXIVA tablets (700 mg) provided similar amprenavir exposures (AUC); however, the C_max of amprenavir after administration of the suspension formulation was 14.5% higher compared with the tablet.

Amprenavir is both a substrate for and inducer of P-glycoprotein.

Effects of Food on Oral Absorption

Administration of a single 1,400-mg dose of LEXIVA tablets in the fed state (standardized high-fat meal: 967 kcal, 67 grams fat, 33 grams protein, 58 grams carbohydrate) compared with the fasted state was associated with no significant changes in amprenavir C_max, T_max, or AUC_0-∞ [see Dosage and Administration (2)].

Administration of a single 1,400-mg dose of LEXIVA oral suspension in the fed state (standardized high-fat meal: 967 kcal, 67 grams fat, 33 grams protein, 58 grams carbohydrate) compared with the fasted state was associated with a 46% reduction in C_max, a 0.72-hour delay in T_max, and a 28% reduction in amprenavir AUC_0-∞.

Distribution

In vitro, amprenavir is approximately 90% bound to plasma proteins, primarily to alpha₁-acid glycoprotein. In vitro, concentration-dependent binding was observed over the concentration range of 1 to 10 mcg per mL, with decreased binding at higher concentrations. The partitioning of amprenavir into erythrocytes is low, but increases as amprenavir concentrations increase, reflecting the higher amount of unbound drug at higher concentrations.

Metabolism

After oral administration, fosamprenavir is rapidly and almost completely hydrolyzed to amprenavir and inorganic phosphate prior to reaching the systemic circulation. This occurs in the gut epithelium during absorption. Amprenavir is metabolized in the liver by the CYP3A4 enzyme system. The 2 major metabolites result from oxidation of the tetrahydrofuran and aniline moieties. Glucuronide conjugates of oxidized metabolites have been identified as minor metabolites in urine and feces.

Elimination

Excretion of unchanged amprenavir in urine and feces is minimal. Unchanged amprenavir in urine accounts for approximately 1% of the dose; unchanged amprenavir was not detectable in feces. Approximately 14% and 75% of an administered single dose of ¹⁴C-amprenavir can be accounted for as metabolites in urine and feces, respectively. Two metabolites accounted for greater than 90% of the radiocarbon in fecal samples. The plasma elimination half-life of amprenavir is approximately 7.7 hours.

Specific Populations

Patients with Hepatic Impairment: The pharmacokinetics of amprenavir have been studied after the administration of LEXIVA in combination with ritonavir to adult HIV-1–infected subjects with mild, moderate, and severe hepatic impairment. Following 2 weeks of dosing with LEXIVA plus ritonavir, the AUC of amprenavir was increased by approximately 22% in subjects with mild hepatic impairment, by approximately 70% in subjects with moderate hepatic impairment, and by approximately 80% in subjects with severe hepatic impairment compared with HIV-1–infected subjects with normal hepatic function. Protein binding of amprenavir was decreased in subjects with hepatic impairment. The unbound fraction at 2 hours (approximate C_max) ranged between a decrease of -7% to an increase of 57% while the unbound fraction at the end of the dosing interval (C_min) increased from 50% to 102% [see Dosage and Administration (2.4)].

The pharmacokinetics of amprenavir have been studied after administration of amprenavir given as AGENERASE capsules to adult subjects with hepatic impairment. Following administration of a single 600-mg oral dose, the AUC of amprenavir was increased by approximately 2.5-fold in subjects with moderate cirrhosis and by approximately 4.5-fold in subjects with severe cirrhosis compared with healthy volunteers [see Dosage and Administration (2.4)].

Patients with Renal Impairment: The impact of renal impairment on amprenavir elimination in adults has not been studied. The renal elimination of unchanged amprenavir represents approximately 1% of the administered dose; therefore, renal impairment is not expected to significantly impact the elimination of amprenavir.

Pregnant Women: Amprenavir pharmacokinetics were studied in pregnant women receiving LEXIVA (700 mg) plus ritonavir (100 mg) twice daily during the second trimester (n = 6) or third trimester (n = 9) and postpartum (n = 9). Compared to postpartum, geometric mean amprenavir AUC was 35% lower in the second trimester and 25% lower in the third trimester (Table 8). This decrease results in amprenavir concentrations that are within the range observed across regimens of LEXIVA in non-pregnant adults and lower concentrations compared with LEXIVA (700 mg) plus ritonavir (100 mg) twice daily in non-pregnant adults (Table 7, Table 8). This decrease is not expected to be considered clinically relevant in patients who are virologically suppressed; however, viral load should be monitored closely to ensure viral suppression is maintained [see Dosage and Administration (2.2), Use in Specific Populations (8.1)]. The amprenavir geometric mean ratio (95% CI) of fetal cord to maternal peripheral plasma concentration (n = 7) was 0.27 (0.24 to 0.30).

Table 8. Geometric Mean (95% CI) Steady-State Plasma Amprenavir Pharmacokinetic Parameters in Pregnant Women Receiving LEXIVA with Ritonavir

a AUC24 was calculated from AUC12 summary data x 2. b Ctau represents the concentration at the end of the dose interval.
Pharmacokinetic Parameter	LEXIVA 700 mg Twice Daily plus Ritonavir 100 mg Twice Daily
	Second Trimester (n = 6)	Third Trimester (n = 9)	Postpartum (n = 9)
AUC12 (mcgh/mL)	26.0 (19.5, 34.6)	30.1 (21.6, 41.9)	39.9 (31.9, 50.1)
AUC24 (mcgh/mL)a	52.0 (39.0, 69.2)	60.2 (43.2, 83.8)	79.8 (63.8, 100.2)
Cmax (mcg/mL)	4.19 (3.19, 5.51)	5.36 (3.98, 7.22)	6.65 (5.24, 8.44)
Ctau (mcg/mL)b	1.31 (0.97, 1.77)	1.34 (0.95, 1.89)	2.03 (1.46, 2.83)

Pediatric Patients: The pharmacokinetics of amprenavir following administration of LEXIVA oral suspension and LEXIVA tablets, with or without ritonavir, have been studied in a total of 212 HIV-1–infected pediatric subjects enrolled in 3 trials. LEXIVA without ritonavir was administered as 30 or 40 mg per kg twice daily to children aged 2 to 5 years. LEXIVA with ritonavir was administered as LEXIVA 30 mg per kg plus ritonavir 6 mg per kg once daily to children aged 2 to 18 years and as LEXIVA 18 to 60 mg per kg plus ritonavir 3 to 10 mg per kg twice daily to children aged at least 4 weeks to 18 years; body weights ranged from 3 to 103 kg.

Amprenavir apparent clearance decreased with increasing weight. Weight-adjusted apparent clearance was higher in children younger than 4 years, suggesting that younger children require higher mg-per-kg dosing of LEXIVA.

The pharmacokinetics of LEXIVA oral suspension in protease inhibitor-naive infants younger than 6 months (n = 9) receiving LEXIVA 45 mg per kg plus ritonavir 10 mg per kg twice daily generally demonstrated lower AUC₁₂ and C_min than adults receiving twice-daily LEXIVA 700 mg plus ritonavir 100 mg, the dose recommended for protease-experienced adults. The mean steady-state amprenavir AUC₁₂, C_max, and C_min were 26.6 mcghour per mL, 6.25 mcg per mL, and 0.86 mcg per mL, respectively. Because of expected low amprenavir exposure and a requirement for large volume of drug, twice-daily dosing of LEXIVA alone (without ritonavir) in pediatric subjects younger than 2 years was not studied.

Pharmacokinetic parameters for LEXIVA administered with food and with ritonavir in this patient population at the recommended weight-band–based dosage regimens are provided in Table 9.

Table 9. Geometric Mean (95% CI) Steady-State Plasma Amprenavir Pharmacokinetic Parameters by Weight in Pediatric and Adolescent Subjects Aged at Least 4 Weeks to 18 Years Receiving LEXIVA with Ritonavir

a Recommended dose for pediatric patients weighing 11 kg to less than 15 kg is based on population pharmacokinetic analysis.
Weight	Recommended Dosage Regimen	Cmax		AUC24		Cmin
		n	(mcg/mL)	n	(mcgh/mL)	n	(mcg/mL)
<11 kg	LEXIVA 45 mg/kg plus Ritonavir 7 mg/kg twice daily	12	6.00 (3.88, 9.29)	12	57.3 (34.1, 96.2)	27	1.65 (1.22, 2.24)
11 kg - <15 kg	LEXIVA 30 mg/kg plus Ritonavir 3 mg/kg twice daily	Not studieda
15 kg - <20 kg	LEXIVA 23 mg/kg plus Ritonavir 3 mg/kg twice daily	5	9.54 (4.63, 19.7)	5	121 (54.2, 269)	9	3.56 (2.33, 5.43)
20 kg - <39 kg	LEXIVA 18 mg/kg plus Ritonavir 3 mg/kg twice daily	13	6.24 (5.01, 7.77)	12	97.9 (77.0, 124)	23	2.54 (2.11, 3.06)
≥39 kg	LEXIVA 700 mg plus Ritonavir 100 mg twice daily	15	5.03 (4.04, 6.26)	15	72.3 (59.6, 87.6)	42	1.98 (1.72, 2.29)

Subjects aged 2 to younger than 6 years receiving LEXIVA 30 mg per kg twice daily without ritonavir achieved geometric mean (95% CI) amprenavir C_max (n = 9), AUC₁₂ (n = 9), and C_min (n = 19) of 7.15 (5.05, 10.1), 22.3 (15.3, 32.6), and 0.513 (0.384, 0.686), respectively.

Geriatric Patients: The pharmacokinetics of amprenavir after administration of LEXIVA to patients older than 65 years have not been studied [see Use in Specific Populations (8.5)].

Male and Female Patients: The pharmacokinetics of amprenavir after administration of LEXIVA do not differ between males and females.

Racial Groups: The pharmacokinetics of amprenavir after administration of LEXIVA do not differ between blacks and non-blacks.

Drug Interaction Studies

[See Contraindications (4), Warnings and Precautions (5.1), Drug Interactions (7).]

Amprenavir, the active metabolite of fosamprenavir, is metabolized in the liver by the cytochrome P450 enzyme system. Amprenavir inhibits CYP3A4. Data also suggest that amprenavir induces CYP3A4. Caution should be used when coadministering medications that are substrates, inhibitors, or inducers of CYP3A4, or potentially toxic medications that are metabolized by CYP3A4. Amprenavir does not inhibit CYP2D6, CYP1A2, CYP2C9, CYP2C19, CYP2E1, or uridine glucuronosyltransferase (UDPGT). Amprenavir is both a substrate for and inducer of P-glycoprotein.

Drug interaction trials were performed with LEXIVA and other drugs likely to be coadministered or drugs commonly used as probes for pharmacokinetic interactions. The effects of coadministration on AUC, C_max, and C_min values are summarized in Table 10 (effect of other drugs on amprenavir) and Table 12 (effect of LEXIVA on other drugs). In addition, since LEXIVA delivers comparable amprenavir plasma concentrations as AGENERASE, drug interaction data derived from trials with AGENERASE are provided in Tables 11 and 13. For information regarding clinical recommendations, [see Drug Interactions (7)].

Table 10. Drug Interactions: Pharmacokinetic Parameters for Amprenavir after Administration of LEXIVA in the Presence of the Coadministered Drug(s)

a Concomitant medication is also shown in this column where appropriate. b Ritonavir Cmax, AUC, and Cmin increased by 63%, 45%, and 13%, respectively, compared with historical control. c Compared with historical control. d Subjects were receiving LEXIVA/ritonavir for 10 days prior to the 4-day treatment period with both ketoconazole and LEXIVA/ritonavir. e Compared with LEXIVA 700 mg/ritonavir 100 mg twice daily for 2 weeks. f Subjects were receiving nevirapine for at least 12 weeks prior to trial. g Clast (C12 h or C24 h). h Doses of LEXIVA and raltegravir were given with food on pharmacokinetic sampling days and without regard to food all other days. i Compared with parallel control group. ↑= Increase; ↓= Decrease; ↔ = No change (↑ or ↓ less than or equal to 10%), NA = Not applicable.
Coadministered Drug(s) and Dose(s)	Dose of LEXIVAa	n	% Change in Amprenavir Pharmacokinetic Parameters (90% CI)
			Cmax	AUC	Cmin
Antacid (MAALOX TC)     30-mL single dose	1,400-mg single dose	30	↓35 (↓24 to ↓42)	↓18 (↓9 to ↓26)	↑14 (↓7 to ↑39)
Atazanavir     300 mg once daily for 10 days	700 mg twice daily plus ritonavir 100 mg twice daily for 10 days	22	↔	↔	↔
Atorvastatin     10 mg once daily for 4 days	1,400 mg twice daily for 2 weeks	16	↓18 (↓34 to ↑1)	↓27 (↓41 to ↓12)	↓12 (↓27 to ↓6)
Atorvastatin     10 mg once daily for 4 days	700 mg twice daily plus ritonavir 100 mg twice daily for 2 weeks	16	↔	↔	↔
Efavirenz     600 mg once daily for 2 weeks	1,400 mg once daily plus ritonavir 200 mg once daily for 2 weeks	16	↔	↓13 (↓30 to ↑7)	↓36 (↓8 to ↓56)
Efavirenz     600 mg once daily plus additional     ritonavir 100 mg once daily for 2 weeks	1,400 mg once daily plus ritonavir 200 mg once daily for 2 weeks	16	↑18 (↑1 to ↑38)	↑11 (0 to ↑24)	↔
Efavirenz     600 mg once daily for 2 weeks	700 mg twice daily plus ritonavir 100 mg twice daily for 2 weeks	16	↔	↔	↓17 (↓4 to ↓29)
Esomeprazole     20 mg once daily for 2 weeks	1,400 mg twice daily for 2 weeks	25	↔	↔	↔
Esomeprazole     20 mg once daily for 2 weeks	700 mg twice daily plus ritonavir 100 mg twice daily for 2 weeks	23	↔	↔	↔
Ethinyl estradiol/ norethindrone     0.035 mg/0.5 mg once daily for 21 days	700 mg twice daily plus ritonavirb 100 mg twice daily for 21 days	25	↔c	↔c	↔c
Ketoconazoled     200 mg once daily for 4 days	700 mg twice daily plus ritonavir 100 mg twice daily for 4 days	15	↔	↔	↔
Lopinavir/ritonavir     533 mg/133 mg twice daily	1,400 mg twice daily for 2 weeks	18	↓13e	↓26e	↓42e
Lopinavir/ritonavir     400 mg/100 mg twice daily for 2 weeks	700 mg twice daily plus ritonavir 100 mg twice daily for 2 weeks	18	↓58 (↓42 to ↓70)	↓63 (↓51 to ↓72)	↓65 (↓54 to ↓73)
Maraviroc     300 mg twice daily for 10 days	700 mg twice daily plus ritonavir 100 mg twice daily for 20 days	14	↓34 (↓25 to ↓41)	↓35 (↓29 to ↓41)	↓36 (↓27 to ↓43)
Maraviroc     300 mg once daily for 10 days	1,400 mg once daily plus ritonavir 100 mg once daily for 20 days	14	↓29 (↓20 to ↓38)	↓30 (↓23 to ↓36)	↓15 (↓3 to ↓25)
Methadone     70 to 120 mg once daily for 2 weeks	700 mg twice daily plus ritonavir 100 mg twice daily for 2 weeks	19	↔c	↔c	↔c
Nevirapine     200 mg twice daily for 2 weeksf	1,400 mg twice daily for 2 weeks	17	↓25 (↓37 to ↓10)	↓33 (↓45 to ↓20)	↓35 (↓50 to ↓15)
Nevirapine     200 mg twice daily for 2 weeksf	700 mg twice daily plus ritonavir 100 mg twice daily for 2 weeks	17	↔	↓11 (↓23 to ↑3)	↓19 (↓32 to ↓4)
Phenytoin     300 mg once daily for 10 days	700 mg twice daily plus ritonavir 100 mg twice daily for 10 days	13	↔	↑20 (↑8 to ↑34)	↑19 (↑6 to ↑33)
Raltegravir     400 mg twice daily for 14 days	1,400 mg twice daily for 14 days (fasted)	14	↓27 (↓46 to ↔)	↓36 (↓53 to ↓13)	↓43g (↓59 to ↓21)
	1,400 mg twice daily for 14 daysh	14	↓15 (↓27 to ↓1)	↓17 (↓27 to ↓6)	↓32g (↓53 to ↓1)
	700 mg twice daily plus ritonavir 100 mg twice daily for 14 days (fasted)	14	↓14 (↓39 to ↑20)	↓17 (↓38 to ↑12)	↓20g (↓45 to ↑17)
	700 mg twice daily plus ritonavir 100 mg twice daily for 14 daysh	12	↓25 (↓42 to ↓2)	↓25 (↓44 to ↔)	↓33g (↓52 to ↓7)
Raltegravir     400 mg twice daily for 14 days	1,400 mg once daily plus ritonavir 100 mg once daily for 14 days (fasted)	13	↓18 (↓34 to ↔)	↓24 (↓41 to ↔)	↓50g (↓64 to ↓31)
	1,400 mg once daily plus ritonavir 100 mg once daily for 14 daysh	14	↑27 (↓1 to ↑62)	↑13 (↓7 to ↑38)	↓17g (↓45 to ↑26)
Ranitidine     300-mg single dose (administered 1 hour before fosamprenavir)	1,400-mg single dose	30	↓51 (↓43 to ↓58)	↓30 (↓22 to ↓37)	↔ (↓19 to ↑21)
Rifabutin     150 mg every other day for 2 weeks	700 mg twice daily plus ritonavir 100 mg twice daily for 2 weeks	15	↑36c (↑18 to ↑55)	↑35c (↑17 to ↑56)	↑17c (↓1 to ↑39)
Tenofovir     300 mg once daily for 4 to 48 weeks	700 mg twice daily plus ritonavir 100 mg twice daily for 4 to 48 weeks	45	NA	NA	↔i
Tenofovir     300 mg once daily for 4 to 48 weeks	1,400 mg once daily plus ritonavir 200 mg once daily for 4 to 48 weeks	60	NA	NA	↔i

Table 11. Drug Interactions: Pharmacokinetic Parameters for Amprenavir after Administration of AGENERASE in the Presence of the Coadministered Drug(s)

a Compared with parallel control group. b Median percent change; confidence interval not reported. c Compared with historical data. ↑ = Increase; ↓ = Decrease; ↔ = No change (↑ or ↓ less than 10%); NA = Cmin not calculated for single‑dose trial.
Coadministered Drug(s) and Dose(s)	Dose of AGENERASEa	n	% Change in Amprenavir Pharmacokinetic Parameters (90% CI)
			Cmax	AUC	Cmin
Abacavir     300 mg twice daily for 2 to 3 weeks	900 mg twice daily for 2 to 3 weeks	4	↔a	↔a	↔a
Clarithromycin     500 mg twice daily for 4 days	1,200 mg twice daily for 4 days	12	↑15 (↑1 to ↑31)	↑18 (↑8 to ↑29)	↑39 (↑31 to ↑47)
Delavirdine     600 mg twice daily for 10 days	600 mg twice daily for 10 days	9	↑40b	↑130b	↑125b
Ethinyl estradiol/ norethindrone     0.035 mg/1 mg for 1 cycle	1,200 mg twice daily for 28 days	10	↔	↓22 (↓35 to ↓8)	↓20 (↓41 to ↑8)
Indinavir     800 mg 3 times a day for 2 weeks (fasted)	750 or 800 mg 3 times a day for 2 weeks (fasted)	9	↑18 (↑13 to ↑58)	↑33 (↑2 to ↑73)	↑25 (↓27 to ↑116)
Ketoconazole     400-mg single dose	1,200-mg single dose	12	↓16 (↓25 to ↓6)	↑31 (↑20 to ↑42)	NA
Lamivudine     150-mg single dose	600-mg single dose	11	↔	↔	NA
Methadone     44 to 100 mg once daily for >30 days	1,200 mg twice daily for 10 days	16	↓27c	↓30c	↓25c
Nelfinavir     750 mg 3 times a day for 2 weeks (fed)	750 or 800 mg 3 times a day for 2 weeks (fed)	6	↓14 (↓38 to ↑20)	↔	↑189 (↑52 to ↑448)
Rifabutin     300 mg once daily for 10 days	1,200 mg twice daily for 10 days	5	↔	↓15 (↓28 to 0)	↓15 (↓38 to ↑17)
Rifampin     300 mg once daily for 4 days	1,200 mg twice daily for 4 days	11	↓70 (↓76 to ↓62)	↓82 (↓84 to ↓78)	↓92 (↓95 to ↓89)
Saquinavir     800 mg 3 times a day for 2 weeks (fed)	750 or 800 mg 3 times a day for 2 weeks (fed)	7	↓37 (↓54 to ↓14)	↓32 (↓49 to ↓9)	↓14 (↓52 to ↑54)
Zidovudine     300-mg single dose	600-mg single dose	12	↔	↑13 (↓2 to ↑31)	NA

Table 12. Drug Interactions: Pharmacokinetic Parameters for Coadministered Drug in the Presence of Amprenavir after Administration of LEXIVA

a Concomitant medication is also shown in this column where appropriate. b Comparison arm of atazanavir 300 mg once daily plus ritonavir 100 mg once daily for 10 days. c Administered as a combination oral contraceptive tablet: ethinyl estradiol 0.035 mg/norethindrone 0.5 mg. d Subjects were receiving LEXIVA/ritonavir for 10 days prior to the 4-day treatment period with both ketoconazole and LEXIVA/ritonavir. e Data represent lopinavir concentrations. f Compared with lopinavir 400 mg/ritonavir 100 mg twice daily for 2 weeks. g Dose normalized to methadone 100 mg. The unbound concentration of the active moiety, R‑methadone, was unchanged. h Subjects were receiving nevirapine for at least 12 weeks prior to trial. i Comparison arm of rifabutin 300 mg once daily for 2 weeks. AUC is AUC(0-48 h). ↑ = Increase; ↓= Decrease; ↔ = No change (↑ or ↓less than 10%); ND = Interaction cannot be determined as Cmin was below the lower limit of quantitation.
Coadministered Drug(s) and Dose(s)	Dose of LEXIVAa	n	% Change in Pharmacokinetic Parameters of Coadministered Drug (90% CI)
			Cmax	AUC	Cmin
Atazanavir     300 mg once daily for 10 daysb	700 mg twice daily plus ritonavir 100 mg twice daily for 10 days	21	↓24 (↓39 to ↓6)	↓22 (↓34 to ↓9)	↔
Atorvastatin     10 mg once daily for 4 days	1,400 mg twice daily for 2 weeks	16	↑304 (↑205 to ↑437)	↑130 (↑100 to ↑164)	↓10 (↓27 to ↑12)
Atorvastatin     10 mg once daily for 4 days	700 mg twice daily plus ritonavir 100 mg twice daily for 2 weeks	16	↑184 (↑126 to ↑257)	↑153 (↑115 to ↑199)	↑73 (↑45 to ↑108)
Esomeprazole     20 mg once daily for 2 weeks	1,400 mg twice daily for 2 weeks	25	↔	↑55 (↑39 to ↑73)	ND
Esomeprazole     20 mg once daily for 2 weeks	700 mg twice daily plus ritonavir 100 mg twice daily for 2 weeks	23	↔	↔	ND
Ethinyl estradiolc     0.035 mg once daily for 21 days	700 mg twice daily plus ritonavir 100 mg twice daily for 21 days	25	↓28 (↓21 to ↓35)	↓37 (↓30 to ↓42)	ND
Dolutegravir     50 mg once daily	700 mg twice daily plus ritonavir 100 mg twice daily	12	↓24 (↓8 to ↓37)	↓35 (↓22 to ↓46)	↓49 (↓37 to ↓59)
Ketoconazoled     200 mg once daily for 4 days	700 mg twice daily plus ritonavir 100 mg twice daily for 4 days	15	↑25 (↑0 to ↑56)	↑169 (↑108 to ↑248)	ND
Lopinavir/ritonavire     533 mg/133 mg twice daily for 2 weeks	1,400 mg twice daily for 2 weeks	18	↔f	↔f	↔f
Lopinavir/ritonavire     400 mg/100 mg twice daily for 2 weeks	700 mg twice daily plus ritonavir 100 mg twice daily for 2 weeks	18	↑30 (↓15 to ↑47)	↑37 (↓20 to ↑55)	↑52 (↓28 to ↑82)
Maraviroc     300 mg twice daily for 10 days	700 mg twice daily plus ritonavir 100 mg twice daily for 20 days	14	↑52 (↑27 to ↑82)	↑149 (↑119 to ↑182)	↑374 (↑303 to ↑457)
Maraviroc     300 mg once daily for 10 days	1,400 mg once daily plus ritonavir 100 mg once daily for 20 days	14	↑45 (↑20 to ↑74)	↑126 (↑99 to ↑158)	↑80 (↑53 to ↑113)
Methadone     70 to 120 mg once daily for 2 weeks	700 mg twice daily plus ritonavir 100 mg twice daily for 2 weeks	19	R-Methadone (active)
			↓21g (↓30 to ↓12)	↓18g (↓27 to ↓8)	↓11g (↓21 to ↑1)
			S-Methadone (inactive)
			↓43g (↓49 to ↓37)	↓43g (↓50 to ↓36)	↓41g (↓49 to ↓31)
Nevirapine     200 mg twice daily for 2 weeksh	1,400 mg twice daily for 2 weeks	17	↑25 (↑14 to ↑37)	↑29 (↑19 to ↑40)	↑34 (↑20 to ↑49)
Nevirapine     200 mg twice daily for 2 weeksh	700 mg twice daily plus ritonavir 100 mg twice daily for 2 weeks	17	↑13 (↑3 to ↑24)	↑14 (↑5 to ↑24)	↑22 (↑9 to ↑35)
Norethindronec     0.5 mg once daily for 21 days	700 mg twice daily plus ritonavir 100 mg twice daily for 21 days	25	↓38 (↓32 to ↓44)	↓34 (↓30 to ↓37)	↓26 (↓20 to ↓32)
Phenytoin     300 mg once daily for 10 days	700 mg twice daily plus ritonavir 100 mg twice daily for 10 days	14	↓20 (↓12 to ↓27)	↓22 (↓17 to ↓27)	↓29 (↓23 to ↓34)
Rifabutin     150 mg every other day for 2 weeks i	700 mg twice daily plus ritonavir 100 mg twice daily for 2 weeks	15	↓14 (↓28 to ↑4)	↔	↑28 (↑12 to ↑46)
(25-O-desacetylrifabutin metabolite)			↑579 (↑479 to ↑698)	↑1,120 (↑965 to ↑1,300)	↑2,510 (↑1,910 to ↑3,300)
Rifabutin + 25-O- desacetylrifabutin metabolite			NA	↑64 (↑46 to ↑84)	NA
Rosuvastatin     10-mg single dose	700 mg twice daily plus ritonavir 100 mg twice daily for 7 days		(↑45)	(↑8)	NA

Table 13. Drug Interactions: Pharmacokinetic Parameters for Coadministered Drug in the Presence of Amprenavir after Administration of AGENERASE

a Compared with historical data. b Median percent change; confidence interval not reported. ↑ = Increase; ↓ = Decrease; ↔= No change (↑ or ↓ less than 10%); NA = Cmin not calculated for single-dose trial; ND = Interaction cannot be determined as Cmin was below the lower limit of quantitation.
Coadministered Drug(s) and Dose(s)	Dose of AGENERASE	n	% Change in Pharmacokinetic Parameters of Coadministered Drug (90% CI)
			Cmax	AUC	Cmin
Abacavir     300 mg twice daily for 2 to 3 weeks	900 mg twice daily for 2 to 3 weeks	4	↔a	↔a	↔a
Clarithromycin     500 mg twice daily for 4 days	1,200 mg twice daily for 4 days	12	↓10 (↓24 to ↑7)	↔	↔
Delavirdine     600 mg twice daily for 10 days	600 mg twice daily for 10 days	9	↓47b	↓61b	↓88b
Ethinyl estradiol     0.035 mg for 1 cycle	1,200 mg twice daily for 28 days	10	↔	↔	↑32 (↓3 to ↑79)
Indinavir     800 mg 3 times a day for 2 weeks (fasted)	750 mg or 800 mg 3 times a day for 2 weeks (fasted)	9	↓22a	↓38a	↓27a
Ketoconazole     400-mg single dose	1,200-mg single dose	12	↑19 (↑8 to ↑33)	↑44 (↑31 to ↑59)	NA
Lamivudine     150-mg single dose	600-mg single dose	11	↔	↔	NA
Methadone     44 to 100 mg once daily for >30 days	1,200 mg twice daily for 10 days	16	R-Methadone (active)
			↓25 (↓32 to ↓18)	↓13 (↓21 to ↓5)	↓21 (↓32 to ↓9)
			S-Methadone (inactive)
			↓48 (↓55 to ↓40)	↓40 (↓46 to ↓32)	↓53 (↓60 to ↓43)
Nelfinavir     750 mg 3 times a day for 2 weeks (fed)	750 mg or 800 mg 3 times a day for 2 weeks (fed)	6	↑12a	↑15a	↑14a
Norethindrone     1 mg for 1 cycle	1,200 mg twice daily for 28 days	10	↔	↑18 (↑1 to ↑38)	↑45 (↑13 to ↑88)
Rifabutin     300 mg once daily for 10 days	1,200 mg twice daily for 10 days	5	↑119 (↑82 to ↑164)	↑193 (↑156 to ↑235)	↑271 (↑171 to ↑409)
Rifampin     300 mg once daily for 4 days	1,200 mg twice daily for 4 days	11	↔	↔	ND
Saquinavir     800 mg 3 times a day for 2 weeks (fed)	750 mg or 800 mg 3 times a day for 2 weeks (fed)	7	↑21a	↓19a	↓48a
Zidovudine     300-mg single dose	600-mg single dose	12	↑40 (↑14 to ↑71)	↑31 (↑19 to ↑45)	NA

Mechanism of Action

Fosamprenavir is a prodrug that is rapidly hydrolyzed to amprenavir by cellular phosphatases in the gut epithelium as it is absorbed. Amprenavir is an inhibitor of HIV-1 protease. Amprenavir binds to the active site of HIV-1 protease and thereby prevents the processing of viral Gag and Gag-Pol polyprotein precursors, resulting in the formation of immature non-infectious viral particles.

Antiviral Activity

Fosamprenavir has little or no antiviral activity in cell culture. The antiviral activity of amprenavir was evaluated against HIV-1 IIIB in both acutely and chronically infected lymphoblastic cell lines (MT-4, CEM-CCRF, H9) and in peripheral blood lymphocytes in cell culture. The 50% effective concentration (EC₅₀) of amprenavir ranged from 0.012 to 0.08 microM in acutely infected cells and was 0.41 microM in chronically infected cells (1 microM = 0.50 mcg per mL). The median EC₅₀ value of amprenavir against HIV-1 isolates from clades A to G was 0.00095 microM in peripheral blood mononuclear cells (PBMCs). Similarly, the EC₅₀ values for amprenavir against monocytes/macrophage tropic HIV-1 isolates (clade B) ranged from 0.003 to 0.075 microM in monocyte/macrophage cultures. The EC₅₀ values of amprenavir against HIV-2 isolates grown in PBMCs were higher than those for HIV-1 isolates, and ranged from 0.003 to 0.11 microM. The anti-HIV-1 activity of amprenavir was not antagonistic in combination with the nucleoside reverse transcriptase inhibitors (NRTIs); abacavir, didanosine, lamivudine, stavudine, tenofovir, and zidovudine; the non-nucleoside reverse transcriptase inhibitors (NNRTIs) delavirdine, efavirenz, and nevirapine; the protease inhibitors (PIs) atazanavir, indinavir, lopinavir, nelfinavir, ritonavir, and saquinavir; and the gp41 fusion inhibitor enfuvirtide. These drug combinations have not been adequately studied in humans.

Resistance

HIV-1 isolates with decreased susceptibility to amprenavir have been selected in cell culture and obtained from subjects treated with fosamprenavir. Genotypic analysis of isolates from treatment-naive subjects failing amprenavir-containing regimens showed substitutions in the HIV-1 protease resulting in amino acid substitutions primarily at positions V32I, M46I/L, I47V, I50V, I54L/M, and I84V, as well as substitutions in the p7/p1 and p1/p6 Gag and Gag-Pol polyprotein precursor cleavage sites. Some of these amprenavir resistance-associated substitutions have also been detected in HIV-1 isolates from antiretroviral-naive subjects treated with LEXIVA. Of the 488 antiretroviral-naive subjects treated with LEXIVA 1,400 mg twice daily or LEXIVA 1,400 mg plus ritonavir 200 mg once daily in Trials APV30001 and APV30002, respectively, isolates from 61 subjects (29 receiving LEXIVA and 32 receiving LEXIVA/ritonavir) with virologic failure (plasma HIV-1 RNA greater than 1,000 copies per mL on 2 occasions on or after Week 12) were genotyped. Isolates from 5 of the 29 antiretroviral-naive subjects (17%) receiving LEXIVA without ritonavir in Trial APV30001 had evidence of genotypic resistance to amprenavir: I54L/M (n = 2), I54L + L33F (n = 1), V32I + I47V (n = 1), and M46I + I47V (n = 1). No amprenavir resistance-associated substitutions were detected in isolates from antiretroviral-naive subjects treated with LEXIVA/ritonavir for 48 weeks in Trial APV30002. However, the M46I and I50V substitutions were detected in isolates from 1 virologic failure subject receiving LEXIVA/ritonavir once daily at Week 160 (HIV-1 RNA greater than 500 copies per mL). Upon retrospective analysis of stored samples using an ultrasensitive assay, these resistant substitutions were traced back to Week 84 (76 weeks prior to clinical virologic failure).

Cross-Resistance

Varying degrees of cross-resistance among HIV-1 protease inhibitors have been observed. An association between virologic response at 48 weeks (HIV-1 RNA level less than 400 copies per mL) and protease inhibitor-resistance substitutions detected in baseline HIV-1 isolates from protease inhibitor-experienced subjects receiving LEXIVA/ritonavir twice daily (n = 88), or lopinavir/ritonavir twice daily (n = 85) in Trial APV30003 is shown in Table 14. The majority of subjects had previously received either one (47%) or 2 protease inhibitors (36%), most commonly nelfinavir (57%) and indinavir (53%). Out of 102 subjects with baseline phenotypes receiving twice-daily LEXIVA/ritonavir, 54% (n = 55) had resistance to at least one protease inhibitor, with 98% (n = 54) of those having resistance to nelfinavir. Out of 97 subjects with baseline phenotypes in the lopinavir/ritonavir arm, 60% (n = 58) had resistance to at least one protease inhibitor, with 97% (n = 56) of those having resistance to nelfinavir.

Table 14. Responders at Trial Week 48 by Presence of Baseline Protease Inhibitor Resistance-Associated Substitutions^a

a Results should be interpreted with caution because the subgroups were small. b Most subjects had greater than 1 protease inhibitor resistance-associated substitution at baseline.
Protease Inhibitor Resistance-Associated Substitutionsb	LEXIVA/Ritonavir Twice Daily (n = 88)		Lopinavir/Ritonavir Twice Daily (n = 85)
D30N	21/22	95%	17/19	89%