Feasibility Study Assessing the Effect of Carbidopa/Levodopa Ratio on Orthostatic Hypotension in Multiple System Atrophy - Parkinsonian Type and Parkinson Disease. (CARBIDOH)

January 28, 2026 updated by: Julien Bally

A Monocentric, Randomized, Double-blind Study to Assess the Feasibility of Conducting a Full-scale Randomized Controlled Trial (RCT) Assessing the Effect of Carbidopa/Levodopa Ratio on Orthostatic Hypotension (OH) in Multiple System Atrophy - Parkinsonian Type (MSA-P) and Parkinson Disease (PD) Patients (CARBIDOH)

This study is aimed at patients with multi-system atrophy - parkinsonian type (P-MSA) or Parkinson's disease (PD) receiving dopaminergic drugs and suffering from orthostatic hypotension (OH).

OH is a drop in blood pressure when standing, which can lead to symptoms of dizziness, lightheadedness, a black veil in front of the eyes and, when severe, can lead to fainting. HO is one of the symptoms present in AMS-P and PD.

The standard treatment for parkinsonian symptoms of slowness and stiffness is the administration of antiparkinsonian drugs containing dopamine. These dopaminergic drugs always contain 1) levodopa (which is the precursor of dopamine) and 2) an enzyme inhibitor, which may be either benserazide (in the case of Madopar® and its generics) or carbidopa (in the case of Sinemet® or Stalevo® and their generics) and whose role is to potentiate the effect of levodopa.

It has long been known that dopaminergic drugs aggravate HO. Through various mechanisms, this worsening of HO is linked as much to levodopa as to the enzyme inhibitor with which it is combined. However, investigators do not know the respective effects of these two molecules on HO.

In this study, investigators examine how the ratio of Carbidopa to levodopa affects HO in the various assays of the dopaminergic drug under study.

Study Overview

Status

Recruiting

Conditions

Intervention / Treatment

Study Type

Interventional

Enrollment (Estimated)

36

Phase

  • Phase 2
  • Phase 1

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Study Locations

  • Switzerland
    • Canton of Vaud
      • Lausanne, Canton of Vaud, Switzerland, 1005
        • Recruiting
        • Centre Hospitalier Universitaire Vaudois (CHUV)
        • Contact:
        • Contact:
      • Lausanne, Canton of Vaud, Switzerland, 1012
        • Recruiting
        • Centre Hospitalier Universitaire Vaudois
        • Contact:

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Child
  • Adult
  • Older Adult

Accepts Healthy Volunteers

No

Description

Inclusion Criteria:

  1. Informed consent form signed.
  2. Patient over 18 years and under 80 years of age.
  3. Patient with Multiple System Atrophy- Parkinsonian type (MSA-P) (confirmed by diagnostic criteria for clinically established and clinically probable multiple system atrophy (11); OR Patient with Parkinson Disease (PD) (12) presenting OH symptoms (getting at least one point at the 3 questions - n° 14, 15 and 16 - of the SCOPA-AUT scale that address orthostatic hypotension symptoms).
  4. Patient currently receiving Dopamine-Replacement Therapy (i.e. Levodopa combined with Carbidopa or Benserazide).

Exclusion Criteria:

  1. Patient unable to stand an overnight (at least 12 hours) withdrawal of their immediate-release DRT (last extended-, delayed-, or controlled-release dosage must be taken minimum 24 hours prior to the test).
  2. Patient with known congestive heart failure, grades C and D, NYHA III and IV.
  3. Patient with dementia (i.e. major cognitive impairment) associated to MSA-P or PD,
  4. Patient with mild cognitive impairment, and unable to provide or understand informed consent, i.e. who does not have full capacity for discernment.
  5. Current participation to other clinical trials.
  6. Pregnant or lactating woman or willing to become pregnant.

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Treatment
  • Allocation: Randomized
  • Interventional Model: Crossover Assignment
  • Masking: Double

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Active Comparator: Ratio 1:10 i.e. 20 mg Carbidopa / 200 mg Levodopa
This Carbidopa / Levodopa IMP ratio will be administered as a single dose, orally, at visit 1 or 2 or 3 (random order).
Drug: Administration of Carbidopa/levodopa
Participants will perform beat-by-beat orthostatic tests (Schellong tests) before and after intake of single doses of carbidopa:levodopa combinations at 3 different ratios
Active Comparator: Ratio 1:4 i.e. 50 mg Carbidopa / 200 mg Levodopa
This Carbidopa / Levodopa IMP ratio will be administered as a single dose, orally, at visit 1 or 2 or 3 (random order).
Drug: Administration of Carbidopa/levodopa
Participants will perform beat-by-beat orthostatic tests (Schellong tests) before and after intake of single doses of carbidopa:levodopa combinations at 3 different ratios
Experimental: Ratio 1:2 i.e. 100 mg Carbidopa / 200 mg Levodopa
This Carbidopa / Levodopa IMP ratio will be administered as a single dose, orally, at visit 1 or 2 or 3 (random order).
Drug: Administration of Carbidopa/levodopa
Participants will perform beat-by-beat orthostatic tests (Schellong tests) before and after intake of single doses of carbidopa:levodopa combinations at 3 different ratios

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Feasibility of future large-scale double-blind randomized controlled trial (RCT)
Time Frame: From enrollment to the end of study at 5 weeks.

The primary objective is to investigate the feasibility of conducting a future large-scale double-blind randomized controlled trial (RCT) assessing the effect on orthostatic hypotension (OH) of different dosages of Carbidopa (20, 50 or 100 mg), for a constant Levodopa dose (200 mg) through:

  • Recruitment rate: Mean number of patients informed per month during the recruitment period, % of patients wiling to participate to the study among the informed patients, % of patients eligible among the informed patients
  • Adherence rate:% of patients completing the study intervention period among randomized patients
  • Retention rate:% of patients showing up at the last follow-up visit among patients who have completed the study intervention period, % of drop-outs among randomized patients at last follow-up visit
  • Data completion rate of the therapeutic effect measures: % of patients with analysable OH data at week 1, 2 and 3.
From enrollment to the end of study at 5 weeks.

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Julien Bally

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

July 18, 2025

Primary Completion (Estimated)

November 1, 2026

Study Completion (Estimated)

November 1, 2026

Study Registration Dates

First Submitted

February 12, 2025

First Submitted That Met QC Criteria

February 12, 2025

First Posted (Actual)

February 18, 2025

Study Record Updates

Last Update Posted (Actual)

January 29, 2026

Last Update Submitted That Met QC Criteria

January 28, 2026

Last Verified

July 1, 2025

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • 2024-02568

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

YES

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

Yes

Studies a U.S. FDA-regulated device product

No

product manufactured in and exported from the U.S.

Yes

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

Clinical Trials on Parkinson Disease

Clinical Trials on Administration of Carbidopa/levodopa

Search Similar Trials

Sponsors and Collaborators

Medical Conditions

Drug Interventions

CROs by country

CROs in Singapore

Conditions

Rare Diseases

Drug Interventions

Dietary Supplements

Sponsor/Collaborators

Locations

Subscribe