Levodopa/Carbidopa

A to Z Drug Facts

(LEE-voe-DOE-puh/CAR-bih-doe-puh)

Sinemet 10/100, Sinemet 25/100, Sinemet 25/250, Sinemet CR,  Apo-Levocarb, Endo Levodopa/Carbidopa, Nu-Levocarb, Pro-Lecarb

Class: Antiparkinson

 Action Levodopa is precursor of dopamine, which is deficient in parkinsonism patients. Carbidopa has no activity of its own but inhibits decarboxylation of levodopa, making it more available to brain.

 Indications Treatment of symptoms of idiopathic Parkinson's disease (paralysis agitans), postencephalitic parkinsonism and symptomatic parkinsonism associated with carbon monoxide and manganese poisoning.

 Contraindications Narrow-angle glaucoma; undiagnosed skin lesions or prior history of suspected melanoma; concurrent use of or within 2 wk of MAO inhibitors.

 Route/Dosage

Individualize by careful titration. Combination tablets are available in ratios of carbidopa to levodopa of 1:4 (25 mg/100 mg) and 1:10 (10 mg/100 mg; 25 mg/250 mg). Tablets of the two ratios may be administered separately or combined prn to provide optimum dosage. Provide at least 70 to 100 mg/day of carbidopa to reduce side effects.

IMMEDIATE-RELEASE TABLETS

ADULTS: Initial dose: PO 1 tablet of 25 mg carbidopa/100 mg levodopa tid or 10 mg carbidopa/100 mg levodopa tid to qid. Dosage may be increased by 1 tablet qd or qod prn (maximum 8 tablets/day).

SUSTAINED-RELEASE TABLETS (50 MG CARBIDOPA/200 MG LEVODOPA)

ADULTS: Initial dose: PO 1 tablet at intervals ³ 6 hr. Adjust dosage based on response. Usual range is 2 to 8 tablets/day in divided doses 4 to 8 hr while awake. Allow at least 3-day interval between adjustments.

 Interactions

Antihypertensive drugs: May cause symptomatic orthostatic hypotension. MAO inhibitors: May result in hypertensive crisis. Use is contraindicated. Phenothiazines, butyrophenones, phenytoin and papaverine: May reduce levodopa efficacy. Tricyclic antidepressants: Rare cases of hypertension and dyskinesia have occurred.

 Lab Test Interferences May cause false-positive reaction for urinary ketone bodies (Clinitest) and false-negative test results with glucose-oxidase methods of testing for glucosuria (Clinistix, Tes-tape).

 Adverse Reactions

CV: Cardiac irregularities; palpitations; hypertension; phlebitis; orthostatic hypotension. CNS: Paranoid delusions; psychotic episodes; depression; suicidal ideation; dementia; convulsions; hallucinations; dizziness; choreiform; dystonic and other involuntary movements. EENT: Diplopia; blurred vision. GI: Nausea; anorexia; vomiting; GI distress; epigastric pain; GI bleeding; dry mouth; duodenal ulcer. GU: Dark urine; urinary retention; urinary incontinence; priapism. HEMA: Hemolytic and nonhemolytic anemia; thrombocytopenia; leukopenia; agranulocytosis. HEPA: Elevated liver function test results; hepatotoxicity. OTHER: Positive Coomb's test; flushing; malaise.

 Precautions

Pregnancy: Safety and effects unknown. Sustained release: Category C. Lactation: Do not give to nursing mothers. Special risk patients: Use drug with caution in patients with severe cardiovascular or pulmonary disease, bronchial asthma, renal, hepatic or endocrine disease. Abrupt withdrawal: Rapid withdrawal of antiparkinson drugs may produce symptoms of neuroleptic malignant syndrome. Dose conversion: Patients previously given levodopa alone should discontinue levodopa use at least 8 hr before starting carbidopa/levodopa. Eventually substitute combination drug at dosage providing about 25% of previous levodopa dose. GI hemorrhage: Upper GI hemorrhage has been reported in patients with prior history of peptic ulcer. MI: Patients with previous history of MI who have residual arrhythmias should have their cardiac function closely monitored on initiating drug dosage adjustment in facility with provisions for intensive cardiac care. Neurologic/psychiatric effects: Levodopa may cause involuntary movement and mental disturbances. Use drug with caution in patients with psychosis. Dyskinesias may occur at lower doses and sooner than with levodopa alone. Dosages should be reduced if necessary.

 Administration/Storage

• Do not crush or allow patient to chew sustained release tablets; however, regular or sustained release tablet may be cut in half.
• Scored immediate-release tablets may be crushed.
• Administer with food to reduce nausea.
• Do not administer with high-protein foods because they reduce absorption of medication.
• Discontinue levodopa ³ 8 hr before initial dose of levodopa/carbidopa.
• Store at room temperature and protect from light.

 Assessment/Interventions

• Obtain patient history, including drug history and any known allergies.
• Complete baseline assessment of parkinsonian symptoms before instituting therapy.
• Review baseline CBC and liver function test results.
• Determine if patient has taken MAO inhibitors within 3 wk of beginning levodopa/carbidopa therapy.
• Assess for adverse reactions and drug interactions throughout course of therapy.
• Observe for therapeutic effects. Parkinsonian movements are reduced for about 5 hr after administration of medication and then gradually increase in intensity.
• Assess for orthostatic hypotension, dizziness and mental changes during initial phase of therapy.
• Assist patient with position change and ambulation during initial therapy to prevent falling.
• Monitor BP and pulse routinely throughout therapy.
• Observe patients closely for possible depression or suicidal ideation.
• Monitor cardiac function closely, especially in patients with history of MI.
• Do not administer if significant changes in BP, pulse or mental status occur. Notify physician.

 Patient/Family Education

• Teach patient and family how to administer tablets correctly; do not crush or chew sustained-release tablets.
• Instruct patient to report the following symptoms to physician: Uncontrollable movements, mood or mental changes, irregular heartbeat, difficult urination, severe or persistent nausea or vomiting, appetite loss, dry mouth, difficulty swallowing or taste distortion.
• Instruct patient to avoid vitamin B₆ (pyridoxine), fortified cereals and otc vitamins because they reduce absorption of medication.
• Inform patient that drug may cause harmless darkening of sweat or urine.
• Advise patient that drug may cause drowsiness and to use caution while driving or performing other tasks requiring mental alertness.
• Instruct patient and family about longer onset of action (» 1 hr) during initial phase of therapy. Reduction of parkinsonian symptoms may take several weeks to months to occur.
• Instruct patient to avoid sudden position changes to prevent orthostatic hypotension.

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Copyright © 2003 Facts and Comparisons
David S. Tatro
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