Molecule

Drug Groups

approved

Description

An antiviral that is used in the prophylactic or symptomatic treatment of influenza A. It is also used as an antiparkinsonian agent, to treat extrapyramidal reactions, and for postherpetic neuralgia. The mechanisms of its effects in movement disorders are not well understood but probably reflect an increase in synthesis and release of dopamine, with perhaps some inhibition of dopamine uptake. [PubChem]

Indication

For the chemoprophylaxis, prophylaxis, and treatment of signs and symptoms of infection caused by various strains of influenza A virus. Also for the treatment of parkinsonism and drug-induced extrapyramidal reactions.

Pharmacology

Amantadine is an antiviral drug which also acts as an antiparkinson agent, for which it is usually combined with L-DOPA when L-DOPA responses decline (probably due to tolerance). It is a derivate of adamantane, like a similar drug rimantadine. The mechanism of action of amantadine in the treatment of Parkinson's disease and drug-induced extrapyramidal reactions is not known. It has been shown to cause an increase in dopamine release in the animal brain, and does not possess anticholinergic activity.

Toxicity

Deaths have been reported from overdose with amantadine. The lowest reported acute lethal dose was 2 grams. Drug overdose has resulted in cardiac, respiratory, renal or central nervous system toxicity. Cardiac dysfunction includes arrhythmia, tachycardia and hypertension. Pulmonary edema and respiratory distress (including ARDS) have been reported. Renal dysfunction including increased BUN, decreased creatinine clearance and renal insufficiency can occur. Central nervous system effects that have been reported include insomnia, anxiety, aggressive behavior, hypertonia, hyperkinesia, tremor, confusion, disorientation, depersonalization, fear, delirium, hallucination, psychotic reactions, lethargy, somnolence and coma. Seizures may be exacerbated in patients with prior history of seizure disorders. Hyperthermia has also been observed in cases where a drug overdose has occurred.

Affected Organisms

Biotransformation

No appreciable metabolism, although negligible amounts of an acetyl metabolite have been identified.

Absorption

Amantadine is well absorbed orally from the gastrointestinal tract.

Half Life

Mean half-lives ranged from 10 to 14 hours, however renal function impairment causes a severe increase in half life to 7 to 10 days.

Protein Binding

Approximately 67% bound to plasma proteins over a concentration range of 0.1 to 2.0 µg/mL.

Elimination

It is primarily excreted unchanged in the urine by glomerular filtration and tubular secretion.

Distribution

* 3 to 8 L/kg [healthy subjects]

Clearance

* 0.2 - 0.3 L/hr/kg
* 0.10 +/- 0.04 L/hr/kg [healthy, elderly male]

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