CARBIDOPA-LEVODOPA
(kar-bi-doe'pa)
Sinemet, Sinemet-CR, Parcopa
CARBIDOPA
Lodosyn
Classifications: autonomic nervous system agent; anticholinergic (parasympatholytic); antiparkinsonism agent
Pregnancy Category: C

Availability

Carbidopa: 25 mg tablet

Carbidopa/Levodopa: 10 mg/100 mg, 25 mg/100 mg, 25 mg/250 mg tablets; 25 mg/100 mg, 50 mg/200 mg sustained-release tablets and orally disintegrating tablets

Actions

When levodopa is given alone, large doses must be administered. Carbidopa prevents peripheral metabolism (decarboxylation) of levodopa and thereby makes more levodopa available for transport to the brain. Carbidopa does not cross blood-brain barrier and therefore does not affect metabolism of levodopa within the brain. Carbidopa also prevents the inhibitory effect of pyridoxine (vitamin B6) on levodopa.

Therapeutic Effects

Effective in management of symptoms of Parkinson's disease and parkinsonism of secondary origin and improving life expectancy and quality of life.

Uses

Symptomatic treatment of idiopathic Parkinson's disease (paralysis agitans), postencephalitic parkinsonism, and parkinsonism following carbon dioxide and manganese intoxication. Carbidopa is available alone from manufacturer, on request by physician, for use with levodopa when separate titration of each agent is indicated, and for investigational purposes.

Contraindications

Hypersensitivity to carbidopa or levodopa; narrow-angle glaucoma; history of or suspected melanoma. Safe use in women of childbearing potential, during pregnancy (category C), in lactation, and in children <18 y not established.

Cautious Use

Cardiovascular, hepatic, pulmonary, or renal disorders; urinary retention; history of peptic ulcer; psychiatric states; endocrine disease; chronic wide-angle glaucoma; seizure disorders.

Route & Dosage

Parkinson's Disease in Patients Not Currently Receiving Levodopa
Adult: PO 1 tablet containing 10 mg carbidopa/100 mg levodopa or 25 mg carbidopa/100 mg levodopa t.i.d., increased by 1 tablet q.d. or q.o.d. up to 6 tablets/d

Patients Receiving Levodopa
Adult: PO 1 tablet of the 25/250 mixture t.i.d. or q.i.d., adjusted by –1 tablet as needed up to 8 tablets/d (start at 20–25% of initial dose of levodopa)

Administration

Oral

Adverse Effects (1%)

Body as a Whole: Hoarseness, unusual breathing patterns, neuroleptic malignant syndrome. CV: Orthostatic hypotension, irregular heart beat, palpitation, arrhythmias, phlebitis, edema. GI: Nausea, anorexia, dry mouth, bruxism, vomiting, excess salivation. Hematologic: Hemolytic and nonhemolytic anemia, thrombocytopenia, agranulocytosis. Metabolic: Abnormal liver function tests, abnormal BUN. CNS: Involuntary movements (dyskinetic, dystonic, choreiform), ataxia, muscle twitching, increase in hand tremor, numbness, headache, dizziness, euphoria, fatigue, confusion, insomnia, nightmares, mental disturbances, anxiety, depression with suicidal tendencies, delirium, seizures. Skin: Body odor, skin rash, dark sweat, loss of hair. Special Senses: Blepharospasm, mydriasis, miosis, blurred vision, diplopia, oculogyric crisis. Urogenital: Dark urine, priapism, urinary frequency, retention, incontinence.

Diagnostic Test Interference

Urine glucose: false-negative tests may result with use of glucose oxidase methods (e.g., Clinistix, TesTape) and false-positive results with copper reduction methods (e.g., Benedict's, Clinitest), especially in patients receiving large doses. It is reported that Clinistix and TesTape may be used if reading is taken at margin of wet and dry tape. There is also the possibility of false-positive tests for urinary ketones by dipstick tests, e.g., Acetest (equivocal), Ketostix, Labstix; false elevation of serum and urinary uric acid levels by colorimetric methods (not with uricase); and interference with urine PKU test results.

Interactions

Drug: mao inhibitors may precipitate hypertensive crisis; tricyclic antidepressants potentiate postural hypotension; phenothiazines, haloperidol may antagonize effects of levodopa; anticholinergic agents may enhance levodopa effects but can exacerbate involuntary movements; methyldopa, guanethidine increase hypotensive and CNS effects; phenytoin, papaverine may interfere with levodopa effects.

Pharmacokinetics

Absorption: 40–70% of carbidopa absorbed after PO dose; carbidopa may enhance absorption of levodopa. Distribution: Widely distributed in most body tissues except CNS; crosses placenta; excreted in breast milk. Elimination: Excreted in urine. Half-Life: 2 h.

Nursing Implications

Assessment & Drug Effects

Patient & Family Education


Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug