Carbidopa monohydrate

What is on this page?

• What is carbidopa monohydrate?
• How does carbidopa monohydrate work?
• Which conditions is it used or studied for?
• How is carbidopa monohydrate given?
• What do the clinical trials show?
• What side effects are known?

What is carbidopa monohydrate?

Carbidopa monohydrate is an aromatic amino acid decarboxylation inhibitor.^[3] It is not used as a treatment on its own. In the EU Clinical Trials Register, the substance is listed as part of a fixed combination in five product records, always together with levodopa.^[1] One of the registered products also contains a third substance, entacapone, and is sold under the trade name Lecigon 20 mg/ml + 5 mg/ml + 20 mg/ml gel for intestinal use.^[1] Another product name in the register is H006629, an oral modified-release capsule.^[2]

and Lobsor Pharmaceuticals AB.^[1] In the United States, an extended-release capsule formulation of carbidopa and levodopa was first approved in 1975.^[3]

How does carbidopa monohydrate work?

Carbidopa blocks an enzyme called aromatic amino acid decarboxylase. This enzyme normally breaks down levodopa in the body before it can reach the brain. When carbidopa is given together with levodopa, more levodopa is able to cross into the brain, where it is converted into dopamine, the chemical messenger that is lacking in Parkinson's disease.^[3] Carbidopa itself does not enter the brain in significant amounts, so its action is mainly outside the central nervous system.

Which conditions is it used or studied for?

• Parkinson's disease — a progressive disorder of the nervous system that affects movement. The authorised Phase 3 trial INITIATE-LECIG is studying an intestinal gel containing carbidopa, levodopa and entacapone in 150 people with Parkinson's disease.^[1]
• Motor fluctuations in advanced Parkinson's disease — the wearing-off and involuntary movements that occur after long-term levodopa treatment. A Phase 3b trial with 91 participants is testing an oral modified-release capsule called IPX203 for this condition.^[2]
• Post-encephalitic parkinsonism — a parkinsonian syndrome that can follow brain inflammation. The US product information lists this as an approved use for the extended-release capsule.^[3]
• Parkinsonism after carbon monoxide or manganese intoxication — a rare form of parkinsonism caused by exposure to these substances. This is also listed in the US product information.^[3]

How is carbidopa monohydrate given?

Carbidopa monohydrate is always given together with levodopa, and in some products also with entacapone. The EU register lists two pharmaceutical forms: a modified-release hard capsule for oral use and an intestinal gel for intestinal use.^[1][2] The oral extended-release capsule described in the US product information is taken three times daily, with or without food, and must not be chewed, divided or crushed.^[3] The intestinal gel is delivered directly into the intestine through a tube, which allows continuous delivery of the medicine.

What do the clinical trials show?

Two clinical trials involving carbidopa monohydrate as part of a combination product are registered in the EU Clinical Trials Information System. Both are authorised, interventional Phase 3 studies in advanced Parkinson's disease.

What are the trials measuring?

The INITIATE-LECIG trial is measuring whether the intestinal gel combination is superior to best medical treatment in reducing hyperdopaminergic symptoms, which are behavioural problems caused by too much dopamine stimulation. The measurement uses the Ardouin Behavioural Scale, comparing scores before treatment and after six months.^[1]

The ADIP study is measuring the change in "good ON time" — the period when Parkinson's symptoms are well controlled — at week 12 compared to baseline. It compares the oral modified-release capsule IPX203 against an immediate-release levodopa regimen.^[2]

Who can take part?

The INITIATE-LECIG trial enrols people with Parkinson's disease, while the ADIP study specifically enrols people with advanced Parkinson's disease and motor fluctuations. The first trial plans to enrol 150 participants, the second 91 participants.^[1][2]

What side effects are known?

The US product information for the extended-release capsule does not list specific side effects in the provided excerpt. It does contain warnings about contraindications with nonselective MAO inhibitors, a class of antidepressants that must not be combined with carbidopa and levodopa.^[3]