Study To Assess Adverse Events and Change in Disease Activity Of 24-hour Continuous Subcutaneous Infusion Of ABBV-951 In Adult Participants With Advanced Parkinson's Disease

Primary Outcome Measures

1. Percentage of Participants with Adverse Event (AEs)
   An AE is defined as any untoward medical occurrence in a participant or clinical investigation participant administered a pharmaceutical product and which does not necessarily have a causal relationship with this treatment. An SAE is an event that results in death, is life-threatening, requires or prolongs hospitalization, results in a congenital anomaly, persistent or significant disability/incapacity or is an important medical event that, based on medical judgment, may jeopardize the subject and may require medical or surgical intervention to prevent any of the outcomes listed above.
2. Percentage of Participants with AEs of Special Interest (AESIs)
   AESIs are defined as AEs from "special situations," such as accidental or intentional overdose, medication error, occupational or accidental exposure, off-label use, drug abuse, drug misuse, or drug withdrawal, all which must be reported whether associated with an AE or not.
3. Percentage Of Participants With Numeric Grade Equal To Or Higher Than 5 On The Infusion Site Evaluation Scale
   The Infusion Site Evaluation Scale will be used to assess infusion sites. Infusion Site Evaluation Scale is an eight-point numeric scale used to assess irritation at the infusion site area (0 being "no evidence of irritation" and 7 being "strong reaction spreading beyond the test site").
4. Percentage Of Participants With Letter Grade Equal To Or Higher Than D On The Infusion Site Evaluation Scale
   The Infusion Site Evaluation Scale will be used to assess infusion sites. Infusion Site Evaluation Scale is an A to G letter grade scale, used to assess irritation at the infusion site area (A being "no finding" to G being "Small petechial erosions and/or scabs").
5. Change From Baseline in Suicidality as assessed by the Columbia-Suicide Severity Rating Scale (C-SSRS)
   C-SSRS is a systematically administered instrument designed to assess suicidal behavior and ideation, track and assess all suicidal events, and assess the lethality of attempts. Any participant who has suicidal behavior or suicidal ideation with plan since the last C-SSRS completed, will be evaluated immediately by the investigator.
6. Change From Baseline in Impulsive-Compulsive Disorders and related behaviors as assessed in Parkinson's Disease- Rating Scale (QUIP-RS)
   The QUIP-RS is a brief, self-completed or rater-administered rating scale to assess the severity of symptoms of impulse control disorders (ICDs) and related behaviors reported to occur in PD. The QUIP-RS uses a 5-point Likert scale that requires individuals to rate the severity of each symptom based on its frequency.
7. Change From Baseline in Cognitive Impairment as Assessed by the Mini-Mental State Examination (MMSE)
   Cognitive impairment is assessed by the Mini-Mental State Examination (MMSE). MMSE is a brief 30-point questionnaire, administered by a trained rater, that provides a quantitative measure of cognitive status in adults and is used widely to screen for cognitive impairment and to estimate the severity of cognitive impairment at a given point in time, to follow the course of changes in a patient over time, and to document response to treatment.
8. Number of Participants with Abnormal Change in Clinical Laboratory Test Results Like Hematology will be Assessed.
   Number of participants with abnormal change in clinical laboratory test results like hematology will be assessed..
9. Number of Participants with Abnormal Change From Baseline in Vital Sign Measurements like Systolic and Diastolic Blood Pressure will be Assessed
   Number of participants with abnormal change from baseline in vital sign measurements like systolic and diastolic blood pressure will be assessed.
10. Change From Baseline in Electrocardiograms (ECGs)
    12-lead resting ECGs will be recorded. Parameters include RR interval, PR interval, QT interval, and QRS duration.

Secondary Outcome Measures

1. Change From Baseline in Average Normalized "On" Time as Assessed by the Parkinson's Disease (PD) Diary
   Change in "On" time without dyskinesia or with non-troublesome dyskinesia as assessed by the PD diary.
2. Change From Baseline in Average Daily Normalized "Off" Time as Assessed by the PD Diary
   Change in average daily normalized "Off" Time (Hours) is assessed based on PD Diary.
3. Change From Baseline in PD Symptoms as Assessed by the MDS-UPDRS Tool Part I
   The MDS-UPDRS is an investigator-used rating tool to follow the longitudinal course of Parkinson's Disease (PD) with scores ranging from 0 to 236 with 236 representing the worst disability, and 0 representing no disability.
4. Change From Baseline in Motor Experiences of Daily Living
   Motor experiences of daily living is assessed by the Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) Part II. The MDS-UPDRS is an investigator-used rating tool to follow the longitudinal course of Parkinson's Disease (PD) with scores ranging from 0 to 236 with 236 representing the worst disability, and 0 representing no disability.
5. Change From Baseline in PD Symptoms as Assessed by the MDS-UPDRS Tool Part III
   The MDS-UPDRS is an investigator-used rating tool to follow the longitudinal course of Parkinson's Disease (PD) with scores ranging from 0 to 236 with 236 representing the worst disability, and 0 representing no disability.
6. Change From Baseline in PD Symptoms as Assessed by the MDS-UPDRS Tool Part IV
   The MDS-UPDRS is an investigator-used rating tool to follow the longitudinal course of Parkinson's Disease (PD) with scores ranging from 0 to 236 with 236 representing the worst disability, and 0 representing no disability.
7. Change From Baseline in PD Symptoms as Assessed by the MDS-UPDRS Tool Parts I-III
   The MDS-UPDRS is an investigator-used rating tool to follow the longitudinal course of Parkinson's Disease (PD) with scores ranging from 0 to 236 with 236 representing the worst disability, and 0 representing no disability.
8. Change From Baseline in Sleep Symptoms
   Sleep symptoms are assessed by the Parkinson's Disease Sleep Scale-2 (PDSS-2). The PDSS-2 consists of 15 questions that evaluate motor and non-motor symptoms at night and upon wakening, as well as disturbed sleep.
9. Change From Baseline in Quality Of Life as Assessed by the PD Questionnaire-39 item (PDQ-39)
   Quality of life is assessed by the PD Questionnaire-39 item (PDQ-39). PDQ-39 is a disease-specific instrument designed to measure aspects of health that are relevant to participants with PD, and which may not be included in general health status questionnaires. Each item is scored on a 5-point scale.
10. Change From Baseline in Health-related Quality of Life as Assessed by EQ-5D-5L
    Health-related quality of life is assessed by EQ-5D-5L. EQ-5D-5L is a standardized instrument that consists of 2 parts: the EQ-5D descriptive system and the EQ visual analogue-scale (EQ-VAS).
11. Percentage Of Participants With Early Morning "Off" Assessed by the PD Diary as Percentage of Participants with early morning "Off" Upon Waking Up
    Early morning "Off" status is assessed by the PD Diary as percentage of participants with early morning "Off" upon waking up.