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AMANTADINE HYDROCHLORIDE

Medical Diagnosis and Drugs, Medications
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
Clcr 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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