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levodopa-carbidopa
Sinemet, Sinemet CR

Pregnancy Risk Category C

How supplied
Tablets:
carbidopa 10 mg with levodopa 100 mg (Sinemet 10-100), carbidopa 25 mg with levodopa 100 mg (Sinemet 25-100), carbidopa 25 mg with levodopa 250 mg (Sinemet 25-250)
Tablets (extended-release):
carbidopa 50 mg with levodopa 200 mg (Sinemet CR); carbidopa 25 mg with levodopa 100 mg.

Action
Levodopa is converted to dopamine in the CNS, increasing dopamine levels in the brain. Carbidopa inhibits the peripheral decarboxylation of levodopa without affecting levodopa's metabolism within the CNS. Therefore, more levodopa is available to be decarboxylated to dopamine in the brain.

Indications & dosage
Idiopathic Parkinson's disease, postencephalitic parkinsonism, and symptomatic parkinsonism resulting from carbon monoxide or manganese intoxication--

Adults:
1 tablet of 25 mg carbidopa and 100 mg levodopa P.O. t.i.d.; then an increase of 1 tablet daily or every other day, p.r.n., to maximum daily dose of 8 tablets. 25 mg carbidopa and 250 mg levodopa or 10 mg carbidopa and 100 mg levodopa tablets are substituted, as needed, to obtain maximum response. Optimum daily dose must be determined by careful adjustment for each patient.
Patients given conventional tablets may receive extended-release tablets; dosage is calculated on current levodopa intake. Initially, extended-release tablets given should amount to 10% more levodopa per day increased, as needed and tolerated, to 30% more levodopa per day. Administered in divided doses at intervals of 4 to 8 hours.

Adverse reactions
CNS:
choreiform, dystonic, dyskinetic movements; involuntary grimacing, head movements, myoclonic body jerks, ataxia, tremor, muscle twitching; bradykinetic episodes; psychiatric disturbances, anxiety, disturbing dreams, euphoria, malaise, fatigue; severe depression, suicidal tendencies, dementia, delirium, hallucinations (may necessitate reduction or withdrawal of drug), confusion, insomnia, agitation.
CV:
orthostatic hypotension, cardiac irregularities.
EENT:
blepharospasm, blurred vision, diplopia, mydriasis or miosis, oculogyric crises, excessive salivation.
GI:
dry mouth, bitter taste, nausea, vomiting, anorexia; constipation; flatulence; diarrhea; abdominal pain.
GU:
urinary frequency, urine retention, urinary incontinence, darkened urine, priapism.
Hematologic:
hemolytic anemia, thrombocytopenia, leukopenia, agranulocytosis.
Hepatic:
hepatotoxicity.
Metabolic:
weight loss (may occur at start of therapy).
Respiratory:
hiccups, hyperventilation.
Skin:
dark perspiration.
Other:
phlebitis.

Interactions
Drug-drug.
Antihypertensives: additive hypotensive effects. Use together cautiously.
Iron salts:
may reduce bioavailability of levodopa and carbidopa. Administer iron 1 hour before or 2 hours after Sinemet dose.
MAO inhibitors:
risk of severe hypertension. Avoid concomitant use.
Papaverine, phenytoin:
antagonism of antiparkinsonian actions. Don't use together.
Phenothiazines, other antipsychotics:
may antagonize antiparkinsonian actions. Use together cautiously.
Drug-herb.
Octacosanol: may promote worsening of dyskinesias. Avoid concomitant use.
Drug-food.
Foods high in protein: decreased absorption of levodopa. Don't give levodopa with high-protein foods.

Effects on diagnostic tests
Drug elevates serum and urinary uric acid levels when colorimetric test methods are used; it may produce false-positive test results for urinary glucose when cupric sulfate reagent is used and false-negative results in tests using glucose oxidase. False-positive results may occur for urine ketone tests using sodium nitroprusside reagent. Levodopa interferes with urine screening tests for phenylketonuria, falsely elevates urinary catecholamine levels, and may falsely decrease urinary vanillylmandelic acid levels.

Contraindications
Contraindicated in patients with hypersensitivity to drug and in those with
angle-closure glaucoma, melanoma, or undiagnosed skin lesions; also contraindicated within 14 days of MAO inhibitor therapy.

Nursing considerations

Patient teaching

*Liquid contains alcohol. **May contain tartrazine.  †Canada  ‡Australia  §U.K.  OTCOver the counter
Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE-THREATENING

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