ENTACAPONE

ENTACAPONE
(en-ta'ca-pone)
Comtan
Classifications: catecholamine o-methyltransferase (comt) inhibitor; antiparkinson agent;
Therapeutic: antiparkinson agent
Prototype: Tolcapone
Pregnancy Category: C

Availability

200 mg tablets

Action

Selective inhibitor of catecholamine O-methyltransferase (COMT). COMT is responsible for metabolizing levodopa to an intermediate compound 3-O-methyldopa, a chemical which interferes with the availability of levodopa to the brain. Therefore, it increases availability of levodopa in CNS.

Therapeutic Effect

Taken with levodopa, it decreases the formation of 3-O-methyldopa, thus increasing the duration of the motor response of the brain to levodopa in Parkinson's disease. Effectiveness is indicated by diminished Parkinson's manifestations.

Uses

Adjunct to levodopa/carbidopa to treat Parkinson's disease.

Contraindications

Hypersensitivity to entacapone; concurrent MAO inhibitors; children; pregnancy (category D).

Cautious Use

Hepatic impairment; biliary obstruction; concomitant administration with CNS depressants; drugs metabolized by COMT (e.g., isoproterenol, epinephrine, etc.); history of hypotension or syncope; lactation.

Route & Dosage

Parkinson's Disease
Adult: PO 200 mg administered with each dose of levodopa/carbidopa up to 8 times/d

Administration

Oral

Give simultaneously with each levodopa/carbidopa dose.
Must be tapered if discontinued. Never discontinue abruptly.
Do not administer to patients receiving nonselective MAO inhibitors.
Store at 15°–30° C (59°–86° F).

Adverse Effects (≥1%)

Body as a Whole: Back pain, fatigue, asthenia. CNS: Dyskinesia, hyperkinesia, hypokinesia, dizziness, anxiety, somnolence, agitation. GI: Taste perversion, nausea, diarrhea, abdominal pain, constipation, vomiting, dry mouth, dyspepsia, flatulence, gastritis. Respiratory: Dyspnea. Skin: Increased sweating. Other: Urine discoloration, purpura.

Interactions

Drug: Extreme caution must be used if administered with a nonselective maoi; bitolterol, dobutamine, dopamine, epinephrine, isoetharine, isoproterenol, methyldopa, norepinephrine may increase heart rates, possibly cause arrhythmias, excessive changes in BP.

Pharmacokinetics

Absorption: Rapidly absorbed, 35% bioavailable. Peak: 1 h. Distribution: Highly protein bound. Metabolism: Extensively metabolized in plasma and erythrocytes. Elimination: Primarily in feces. Half-Life: 2.4 h (terminal).

Nursing Implications

Assessment & Drug Effects

Monitor carefully for hyperpyrexia, confusion, or emergence of Parkinson's S&S during drug withdrawal.
Monitor for orthostatic hypotension & worsening of dyskinesia or hyperkinesia.
Lab tests: Hgb and serum ferritin levels with prolonged therapy.

Patient & Family Education

Take with levodopa/carbidopa; not effective alone.
Do not discontinue abruptly; gradually reduce dosage.
Exercise caution when rising from a sitting or lying position because faintness/dizziness can occur.
Exercise caution with hazardous activities until reaction to the drug is known.
Harmless brownish-orange discoloration of urine is possible.
Report unusual adverse effects (e.g., hallucinations/unexplained diarrhea).

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

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