Carbidopa and levodopa

Generic name: Carbidopa and levodopa

Drug class: Carbidopa: Aromatic L-amino acid decarboxylase inhibitor; Levodopa: Dopamine precursor

Dosage form: Oral tablets (immediate-release, extended-release, orally disintegrating), extended-release capsules, enteral suspension

Route of administration: Oral, enteral (via feeding tube)

Dose: Dosing varies based on formulation and individual patient needs. Typically, initial doses range from 25 mg carbidopa/100 mg levodopa to 50 mg carbidopa/200 mg levodopa, taken 2-3 times daily. Adjustments are made based on therapeutic response and tolerability. For enteral suspension, dosing is individualized and administered via a pump system.

Mechanism of action: Levodopa is converted to dopamine in the brain, improving motor control. Carbidopa inhibits peripheral aromatic L-amino acid decarboxylase, preventing premature conversion of levodopa to dopamine outside the brain, thereby reducing side effects like nausea and increasing the amount of levodopa available to cross the blood-brain barrier.

Drug usage cases:

• Parkinson’s disease
• Parkinsonism due to encephalitis
• Parkinsonism caused by carbon monoxide or manganese poisoning
• Dopamine-responsive dystonia
• Restless legs syndrome

Drug contraindications:

• Hypersensitivity to carbidopa, levodopa, or any component of the formulation
• Narrow-angle glaucoma
• Concurrent use with non-selective monoamine oxidase inhibitors (e.g., isocarboxazid, phenelzine) within the past 14 days

Side effects:

• Common: Nausea, vomiting, dizziness, orthostatic hypotension, dyskinesias (involuntary movements)
• Serious: Depression, suicidal thoughts, psychosis, hallucinations, impulse control disorders (e.g., compulsive gambling, hypersexuality), sudden onset of sleepiness, melanoma (in patients with undiagnosed skin lesions)

Warnings:

• Monitor for signs of depression and suicidal ideation
• Use caution in patients with a history of melanoma or undiagnosed skin lesions
• Be aware of potential for sudden onset of sleepiness; patients should avoid driving or operating heavy machinery until they know how the medication affects them
• Gradual dose adjustments may be necessary to minimize side effects
• Monitor blood pressure regularly, especially during dose adjustments
• Discontinue use if a hypersensitivity reaction occurs

Use during pregnancy or breastfeeding:

Carbidopa and levodopa should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. It is not known whether carbidopa and levodopa are excreted in human milk. Caution should be exercised when administering this combination to a nursing woman, and a decision should be made whether to discontinue nursing or the drug, considering the importance of the drug to the mother.