AMANTADINE HYDROCHLORIDE

AMANTADINE HYDROCHLORIDe

(a-man'ta-deen)

Symmetrel
Classifications: antiviral; anticholinergic; antiparkinson agent;
Therapeutic:antiviral; antiparkinson agent
Pregnancy Category: C

Availability

100 mg capsules; 50 mg/5 mL syrup

Action

Because it does not suppress antibody formation, it can be administered for interim protection in combination with influenza A virus vaccine until antibody titer is adequate or to augment prophylaxis in a previously vaccinated individual. Mechanism of action in parkinsonism may be related to release of dopamine and other catecholamines from neuronal storage sites.

Therapeutic Effect

Active against several strains of influenza A virus; not effective against influenza B infections.

Uses

In initial therapy or as adjunct with anticholinergic drugs or levodopa in treatment of all forms of parkinsonism (arteriosclerotic, idiopathic, postencephalitic) and for relief of drug-induced extrapyramidal reactions and symptomatic parkinsonism caused by carbon monoxide poisoning. Also used for prophylaxis and symptomatic treatment of influenza A infections.

Unlabeled Uses

Primary enuresis, pseudosclerosis, neuroleptic malignant syndrome (NMS), management of cocaine dependency and withdrawal.

Contraindications

Hypersensitivity to amantadine or rimantadine, closed angle glaucoma; suicidal ideation; pregnancy (category C); lactation. Safety in children <1 y is not established.

Cautious Use

History of epilepsy or other types of seizures; CHF, peripheral edema, orthostatic hypotension; recurrent eczematoid dermatitis; psychoses, severe psychoneuroses; hepatic disease; renal impairment; older adults with cerebral arteriosclerosis.

Route & Dosage

Influenza A
Adult: PO 200 mg once/d or 100 mg q12h
Child (1–9 y): PO 4.4–8.8 mg/kg in 2–3 equal doses (max: 150 mg/d)

Parkinsonism
Adult: PO 100 mg 1–2 times/d, start with 100 mg/d if patient is on other antiparkinsonism medications

Drug-Induced Extrapyramidal Symptoms
Adult: PO 100 mg b.i.d. (max: 400 mg/d if needed)

Renal Impairment
Cl_cr 40–60 mL/min: 100 mg/d; 30–40 mL/min: 200 mg 2 times/wk; 10–20 mL/min: 100 mg 3 times/wk

Administration

Oral

Give with water, milk, or food.
Use supplied calibrated device for measuring syrup formulation.
Influenza prophylaxis: Drug should be initiated when exposure is anticipated and continued for at least 10 d.
Note: Used in conjunction with influenza A vaccine (generally in high-risk patients who have not been vaccinated previously) until protective antibodies develop (10–21 d) after vaccine administration.
Schedule medication in the morning or, with q12h dosing, schedule 2nd dose several hours before bedtime. If insomnia is a problem, suggest patient limit number of daytime naps.
Store in tightly closed container preferably at 15°–30° C (59°–86° F) unless otherwise directed by manufacturer. Avoid freezing.

Adverse Effects (≥1%)

CNS: Dizziness, light-headedness, headache, ataxia, irritability, anxiety, nervousness, difficulty in concentrating, mood or other mental changes, confusion, visual and auditory hallucinations, insomnia, nightmares, convulsions. CV: Orthostatic hypotension, peripheral edema, dyspnea. Special Senses: Blurring or loss of vision. GI: Anorexia, nausea, vomiting, dry mouth. Hematologic: Leukopenia.

Interactions

Drug: Alcohol enhances CNS effects; may potentiate effects of anticholinergics.

Pharmacokinetics

Absorption: Almost completely absorbed from GI tract. Onset: Within 48 h. Peak: 1–4 h. Distribution: Through body fluids. Metabolism: Not metabolized. Elimination: 90% unchanged in urine. Half-Life: 9–37 h (prolonged in renal insufficiency).

Nursing Implications

Assessment & Drug Effects

Monitor effectiveness. Note that with parkinsonism, maximum response occurs within 2 wk–3 mo. Effectiveness may wane after 6–8 wk of treatment; report change to physician.
Monitor and report: Mental status changes; nervousness, difficulty concentrating, or insomnia; loss of seizure control; S&S of toxicity, especially with doses above 200 mg/d.
Establish a baseline profile of the patient's disabilities to accurately differentiate disease symptoms and drug-induced neuropsychiatric adverse reactions.
Monitor vital signs for at least 3 or 4 d after increases in dosage; also monitor urinary output.
Lab tests: pH and serum electrolytes.
Monitor for and report reduced salivation, increased akinesia or rigidity, and psychological disturbances that may develop within 4–48 h after initiation of therapy and after dosage increases with parkinsonism.

Patient & Family Education

Note: For influenza take within 24 h but no later than 48 h after onset of symptoms for effective response and continue for 24–48 h after symptoms disappear; contact physician if no improvement within this time.
Make all position changes slowly, particularly from recumbent to upright position, in order to minimize dizziness.
Report any of the following to physician: Shortness of breath, peripheral edema, significant weight gain, dizziness or lightheadedness, inability to concentrate, and other changes in mental status, difficulty urinating, and visual impairment.
Do not drive and exercise caution with potentially hazardous activities until response to the drug is known.
Note: People with Parkinson's disease should not discontinue therapy abruptly; doing so may precipitate a parkinsonian crisis with severe akinesia, rigidity, tremor, and psychic disturbances. Adhere to established dosage regimen.

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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