Carbidopa

FDA label

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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

Available strengths

• tab 25 mg

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