BTRX-246040 Study in Participants With Parkinson's Disease With Motor Fluctuations

Inclusion Criteria: * Diagnosed with Parkinson's disease (PD), consistent with the United Kingdom PD Society Brain Bank Criteria for the Diagnosis of PD * Men or women ≥ 30 years old and ≤ 76 years old * Female participants must be either surgically sterilized or 2 years post menopausal at screening * Modified Hoehn and Yahr Staging ≤ 3 in the ON state * Montreal Cognitive Assessment (MoCA) Score ≥ 26 * Currently has a clear and decisive response to levodopa, and receiving a stable dose of levodopa (at least 4 doses per day of levodopa or ≥ 3 doses per day of RytaryTM (carbidopa and levodopa) extended-release capsules for at least 4 weeks prior to screening) * Experiencing motor fluctuations during waking hours with at least 2 hours of OFF periods each day, including predictable early morning OFF periods, based on participant assessment * Able to participate in the study in the practically defined OFF state * All anti-parkinsonian medications maintained at a stable dose for at least 4 weeks prior to the initial Screening Visit with the exception of monoamine oxidase B (MAO-B) inhibitors, which must be maintained at a stable level for at least 8 weeks prior to the screening visit * Approved by a central Enrollment Authorization Committee as meeting entry criteria and being a suitable candidate for the study * Male participants agree to use a reliable method of birth control during the study and for at least 90 days following the last dose of BTRX-246040 or placebo * Informed and given ample time and opportunity to think about his/her participation in this study and has given his/her written informed consent on an Institutional Review Board (IRB) or Independent Ethics Committee (IEC) approved consent form * Judged to be reliable and able to keep all appointments for clinic visits, tests, and procedures, including venipuncture, and examinations required by the protocol Exclusion Criteria: * Diagnosis of secondary or an atypical Parkinsonian syndrome * Severe disabling dyskinesia * Clinically significant psychosis or hallucinations or history of psychosis in past 6 months * History of previous neurosurgery for PD * Currently or previously on Duopa/Duodopa * Currently taking apomorphine * Has a diagnosis or history of a substance related disorder per Diagnostic and Statistical Manual of Mental Disorders V edition (DSM-V) criteria (including alcohol but excluding nicotine and caffeine), during the 12 months prior to the Screening Visit * Medical or recreational use of marijuana in the 6 months prior to the Screening Visit * Has tested positive at the Screening Visit for drugs of abuse (opiates, cannabinoids, methadone, cocaine, and amphetamines \[including ecstasy\]) * Active suicidal ideation within 1 year prior to the Screening Visit as evidenced by answering "yes" to Questions 4 or 5 on the suicidal ideation portion of the Columbia- Suicide Severity Rating Scale (C-SSRS) or attempted suicide within the last 1 year * Current major depressive episode or a Beck Depression Inventory-II (BDI-II) score above 19. Participants receiving treatment for depression with antidepressants may be enrolled if they have been on a stable daily dose for at least 8 weeks before the Screening Visit and are clinically stable in the opinion of the Principal Investigator * Currently or within 8 weeks of screening receiving bupropion * Exposure to neuroleptics (antipsychotic drugs) for more than 1 month within the past 2 years, or any exposure within the past year * Any malignancy in the 5 years prior to randomization (excluding successfully treated basal cell carcinoma of the skin or cervical carcinoma in situ) * Current or previous diagnosis of malignant melanoma or the presence of any suspicious skin lesion based on physical exam findings * Any other clinically significant medical condition or circumstance prior to randomization that, in the opinion of the Investigator, could affect participant safety, preclude evaluation of response, interfere with the ability to comply with study procedures, or prohibit completion of the study (e.g., uncontrolled diabetes mellitus, renal or hepatic impairment, coronary artery disease, evidence of significant active cardiac, respiratory, or hematologic disease, cancer with \< 5 year remission (excluding successfully treated basal cell carcinoma of the skin or cervical carcinoma in situ), chronic pain, fibromyalgia or gastric bypass) * Prior seizures (other than childhood febrile seizure) or other condition that would place the participant at increased risk of seizures or is taking anticonvulsants for seizure control * History of serious head injury (e.g., skull fracture, cerebral contusion, or trauma resulting in prolonged unconsciousness), intracranial neoplasm or hemorrhage * Orthostatic hypotension that is symptomatic or requires medication * Participation in another study of an investigational medicinal product (IMP) or medical device currently or in the last 30 days or within 5 half-lives of the IMP (whichever is longer) prior to Screening * Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) levels ≥ 2x upper limit of normal (ULN) or glomerular filtration rate ≤ 60 mL/min at Visit 1 (screening) * Nephritic syndrome, end-stage renal disease (and using renal replacement therapy such as hemodialysis or peritoneal dialysis), or a serum creatinine ≥ 2 mg/dL (≥ 172 μmol/L) at the Screening Visit * Any other clinically significant abnormalities (i.e., laboratory deviations requiring acute medical intervention or further medical evaluation) in laboratory results at screening including clinical chemistries, hematology, and urinalysis, that, in the judgment of the Investigator, should preclude a participant's participation at study entry * Electrocardiogram (ECG) abnormalities at Visit 1 (screening) or Visit 2 that, in the judgment of the Investigator, are clinically significant related to the participant's participation * Using the following concomitant medications (contact the Sponsor-designated medical monitor to determine eligibility when in doubt): 1. proton pump inhibitors within 5 half-lives of Screening 2. fluoxetine and irreversible monoamine oxidase inhibitors within 4 weeks of Screening * Currently taking or have taken, within 5 half-lives of Screening, any medications or supplements that are strong inhibitors or inducers of CYP3A4 * A known hypersensitivity to gelatin capsules * Investigator site personnel directly affiliated with this study, and/or their immediate families. Immediate family is defined as a spouse, parent, child, or sibling, whether biological or legally adopted * Employees of the Sponsor or of any third-party organizations involved in study who require exclusion of their employees * Have participated in a clinical trial or any other type of medical research judged by the Investigator to be scientifically or medically incompatible with this study within 30 days prior to Visit 1 (screening) * Previous completion or withdrawal from this study or any other study investigating BTRX-246040 (previously called LY2940094)