Carbidopa
LODOSYN
What it isPeripheral aromatic amino-acid decarboxylase inhibitor; used only with levodopa for Parkinson disease.
Why this oneBlocking peripheral conversion sends more levodopa to the brain while sharply reducing nausea and hypotension.
What limits itIt has no antiparkinsonian effect alone; inadequate carbidopa permits peripheral levodopa toxicity when formulations are switched.
FDA-approved for
- Parkinson disease (with levodopa) (1975)
FDA label
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| FDA dosing | Population | Start | Target | Max |
|---|---|---|---|---|
| Parkinson's disease/parkinsonism - added to carbidopa-levodopa when daily carbidopa is inadequate (<70 mg/day) | Adults | 25 mg with first daily dose of carbidopa-levodopa; additional 12.5-25 mg may be given with each subsequent dose | Most respond to 1:10 carbidopa:levodopa with carbidopa >=70 mg/day | 200 mg/day carbidopa (total from all products) |
| Parkinson's disease/parkinsonism - separate titration with levodopa | Adults | 25 mg TID-QID, given at same time as levodopa (start levodopa at 20-25% of previous levodopa-alone daily dose) | Individualized | 200 mg/day carbidopa |
Titration Adjust by adding or omitting one-half or one tablet per day; monitor closely - responses (incl. dyskinesias) occur faster than with levodopa alone
Renal Undefined (periodic renal function evaluation recommended during extended therapy)
Hepatic Undefined (periodic hepatic function evaluation recommended during extended therapy)
No antiparkinsonian effect alone - for use only with levodopa or carbidopa-levodopa; does not reduce central (CNS) adverse effects of levodopa
Instructions
- Allow >=12 h between last dose of levodopa alone and starting carbidopa + levodopa
- Give carbidopa and levodopa at the same time
- Do not abruptly reduce or discontinue - hyperpyrexia/confusion resembling NMS reported, esp. with neuroleptics
- If therapy interrupted temporarily, observe for NMS-like symptoms; resume usual dose once oral intake possible
Contraindications
- Nonselective MAOIs with levodopa or carbidopa-levodopa (discontinue >=2 weeks before starting levodopa); MAO-B-selective inhibitors (e.g., selegiline) at recommended doses may be used concomitantly
- Narrow-angle glaucoma (levodopa or carbidopa-levodopa products, with or without carbidopa)
Cautions
- Falling asleep during activities of daily living/somnolence (incl. driving) with carbidopa-levodopa - reassess; advise against driving if it occurs
- Hyperpyrexia and confusion resembling NMS with abrupt dose reduction or withdrawal
- Dyskinesias occur sooner and at lower levodopa doses; may require dose reduction (blepharospasm may be early sign of excess)
- Depression with suicidal tendencies - observe carefully
- Avoid in major psychotic disorder - risk of exacerbating psychosis
- Impulse control/compulsive behaviors (gambling, hypersexuality)
- Increased melanoma risk in Parkinson disease - periodic skin examinations
- Periodic hepatic, hematopoietic, cardiovascular, and renal evaluations during extended therapy
- Elderly: start at low end of dosing range
Adverse reactions
- With levodopa: dyskinesias (choreiform, dystonic, other involuntary movements) - most common
- Nausea
- Psychotic episodes (delusions, hallucinations, paranoid ideation)
- Depression with or without suicidal tendencies
- Dementia
- Confusion
- Dizziness/orthostatic hypotension
- Somnolence
- Dark saliva/sweat/urine
Pregnancy No adequate studies; levodopa crosses placenta (fetal carbidopa minimal); use only if benefit justifies fetal risk
Lactation Unknown whether carbidopa is excreted in human milk; decide whether to discontinue nursing or the drug
NO BOXED WARNINGS
Principal riskLittle on its own; see levodopa
Cost, est. cash$10–$500/month
Generic entry2014
Classes and tags
Clinical profile
Legacy pregnancy categoryUnknown / historical label unavailable
Defining liabilityOrthostasis, hallucinations, dyskinesia and impulse-control symptoms; abrupt withdrawal can be hazardous.
Mechanism of action: Carbidopa ballicule
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