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NCT Number: NCT07793461

Gastrointestinal Dopamine Decarboxylase and Levodopa Pharmacokinetics

The main treatment for Parkinson's disease is a medication called levodopa. Levodopa has to be absorbed from the gut and travel to the brain to work, but a naturally occurring enzyme in the lining of the stomach, called dopamine decarboxylase (AADC), can break some of it down before it ever reaches the brain. We do not yet know whether people whose stomachs have more of this enzyme absorb less of their levodopa dose, have worsened gastrointestinal (GI) symptoms associated with levodopa intake, and whether that affects how well the medication controls their movement symptoms. This research may help doctors understand why levodopa works better in some people with Parkinson's disease than others, which could help improve treatment in future.

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Key information

Conditions

Parkinson's Disease Basal Ganglia Diseases Brain Diseases Central Nervous System Diseases Movement Disorders Nervous System Diseases Neurodegenerative Diseases Parkinson Disease Parkinsonian Disorders Synucleinopathies

Sex eligibility

All sexes

Study type

Interventional

Phase

Phase 4

Primary location

About this study

Patients will be asked to fast overnight prior to the study visit, including holding any doses of dopamine replacement therapy that they may be prescribed, including levodopa or equivalents, and any promotility agents, including cholinesterase inhibitors or peripherally-restricted dopamine antagonists (ie. Domperidone), that may impact gastric transit.

At the start of the study visit, patients will undergo a neurological exam by a study investigator blinded to which study group the patient belongs. Exams will be performed according to the Movement Disorder Society-Sponsored Revision of the Unified Parkinson's Disease Rating Scale (MDS-UPDRS) Part III, a validated clinical score of motor impairment in Parkinson's disease (PD). They will also undergo a baseline blood draw (5.5 mLs) through an indwelling venous cannula in the antecubital vein. Immediately afterwards, a single oral dose of levodopa (100 mg) obtained through the BIDMC research pharmacy with a standard volume of water (100 mL). Repeat blood samples will be collected immediately after oral levodopa ingestion (T=0) and then repeated every ½ hour until T=4 hours for a total of 10 draws, including the baseline. The initial placement of indwelling venous cannula will mitigate the necessity for repeated venipuncture during the study visit. At each ½ hour interval, additionally, patients will undergo repeat MDS-UPDRS-III assessments. After the 4-hour study concludes, the patient will be allowed to consume any food they would like and can resume home medications as previously prescribed clinically. Blood samples will be centrifuged to separate plasma and immediately frozen at -80oC until analysis by an investigator blinded to which study group the patient belongs.

Separately, patients' prior clinically-obtained gastric biopsy blocks will be requested from BIDMC pathology (as otherwise discarded specimen) and stained for presence of AADC. This will not require any further time or visits from the patient themselves.

Who can participate

Healthy volunteers accepted: No

Only the study team can determine whether someone qualifies for participation.

Inclusion criteria

  • Parkinson's disease
  • Gastric biopsies previously obtained during clinically-indicated EGD procedure
  • Taking dopamine replacement therapy currently

Exclusion criteria

  • No history of Parkinson's disease

Treatment and study plan

Levodopa (L-dopa)

Drug

levodopa will be administered to all participants in this single arm study

Primary outcomes

  1. levodopa pharmacodynamics

    Time frame: 0-4 hours after oral levodopa ingestion.

    Peripheral levodopa levels will be assessed via blood draw to determine time (in minutes) to reach maximum concentration in the blood. Lower Tmax indicates quicker bioavailability.

Secondary outcomes

  1. The Movement Disorder Society-Sponsored Revision of the Unified Parkinson's Disease Rating Scale (MDS-UPDRS) part III score

    Time frame: 0-4 hours after oral levodopa ingestion

    Neurological symptoms will be assessed during study period. A lower score indicates less severe symptoms.

Study contacts

Contact information is provided by the study sponsor or research team.

Trisha S Pasricha, MD, MPH

CONTACT

[email protected]

(617) 754-8888

Sponsors and collaborators

Lead sponsor

Beth Israel Deaconess Medical Center

Other

Collaborators

  • National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)

Registry information

Important dates

Study start
2027
Primary completion
2030
Study completion
2030
First posted
Aug 28, 2026
Registry last updated
Aug 28, 2026

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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