Section 03 · Monograph
Carbidopa
Reviewed Nov 2026FDA label
LodosynDOPA decarboxylase inhibitor
- Forms
- Tab: 25mg
- Dose
- 25mg with each levodopa dose (target 70-100mg/day; max 200mg/day)
- MOA
- Blocks peripheral levodopa-to-dopamine conversion
Indications
- Used with levodopa or carbidopa-levodopa to reduce peripheral levodopa side effects (nausea, vomiting) and increase levodopa delivery to the brain in Parkinson's diseaseFDA-labeled
Mechanism of Action
- Peripheral DOPA decarboxylase inhibitor that does not cross the blood-brain barrier, blocking conversion of levodopa to dopamine outside the CNS
Full Dosing
Adult / usual
- 25mg with each levodopa dose to reach about 70-100mg/day of total carbidopa; maximum 200mg/day
- Patients on carbidopa-levodopa with persistent nausea may add 25mg carbidopa per dose
Contraindications
- Concomitant nonselective MAO inhibitors (or within 2 weeks)
- Known hypersensitivity
Drug Interactions
- Nonselective MAOIs contraindicated
- Iron salts reduce levodopa absorption
- High-protein meals reduce levodopa absorption
Adverse Effects
- Dyskinesia and nausea (usually reduced by adding carbidopa)
- Hallucinations and sleepiness
- Orthostatic hypotension
Monitoring Parameters
- Motor fluctuations and dyskinesia
- Blood pressure
- Mental status
Pregnancy & Lactation
- Limited human data; use only if benefit justifies risk