Action

Inhibits COMT, the primary enzyme involved in metabolizing levodopa. This inhibition increases levodopa blood level and duration of action, easing symptoms of Parkinson's disease.

Availability

Tablets: 200 mg

Indications and dosages

➣ Adjunctive treatment of idiopathic Parkinson's disease in patients experiencing wearing off of carbidopa-levodopa effects

Adults: 200 mg P.O. with each carbidopa-levodopa dose, to a maximum of eight times daily (1,600 mg)

Contraindications

• Hypersensitivity to drug

Precautions

Use cautiously in:

• hepatic or renal dysfunction, hypertension, heart disease

• pregnant and breastfeeding patients.

Administration

• Give without regard to food.

• Administer at same time as carbidopa-levodopa. Make sure patient swallows tablet whole.

See Don't withdraw drug abruptly.

Adverse reactions

CNS: dizziness, depression, drowsiness, disorientation, memory loss, agitation, delusions, hallucinations, paranoia, euphoria, dyskinesia, hyperkinesia, light-headedness, paresthesia, heaviness of limbs, numbness of fingers

CV: tachycardia, orthostatic hypotension, hypertension

GI: nausea, vomiting, epigastric pain, flatulence

GU: urine discoloration

Respiratory: upper respiratory tract infection, dyspnea, sinus congestion

Other: fever

Interactions

Drug-drug. Ampicillin, chloramphenicol, cholestyramine, erythromycin, probenecid, rifampin: decreased entacapone excretion

Bitolterol, dobutamine, dopamine, epinephrine, isoetherine, isoproterenol, methyldopa, norepinephrine: increased heart rate, increased risk of arrhythmias, excessive blood pressure changes

MAO inhibitors: increased risk of toxicity

Drug-behaviors. Alcohol use: increased risk of adverse reactions

Patient monitoring

• Monitor vital signs, watching especially for orthostatic hypotension.

• Evaluate neurologic status closely. Check for hallucinations and new onset or exacerbation of dyskinesia.

• Assess respiratory status, particularly for dyspnea and signs and symptoms of upper respiratory tract infection.

• Monitor nutritional and hydration status if patient experiences vomiting.

Patient teaching

• Instruct patient to swallow tablet whole and to take it at same time as carbidopa-levodopa.

See Caution patient not to stop taking drug abruptly.

• Advise patient to move slowly when sitting up or standing, to avoid dizziness or light-headedness from sudden blood pressure decrease.

• Caution patient to avoid driving and other hazardous activities until drug no longer affects concentration and alertness.

See Instruct patient (and caregiver) to institute safety measures at home to prevent injury related to disease or drug's adverse CNS effects.

• As appropriate, review all other significant adverse reactions and interactions, especially those related to the drugs and behaviors mentioned above.