Classification: Antiviral and antiparkinson agent
See Also: See also Antiviral Drugs.
Action/Kinetics: Believed to prevent penetration of the virus into cells, possibly by inhibiting uncoating of the RNA virus. May also prevent the release of infectious viral nucleic acid into the host cell. The reaction appears to be virus specific for influenza A but not host specific. The drug reduces symptoms (70% to 90% effective) of viral infections if given within 24-48 hr after onset of illness. For the treatment of parkinsonism, amantadine may increase the release of dopamine from dopaminergic nerve terminals in the substantia nigra of parkinson clients, resulting in an increase in dopamine levels in dopaminergic synapses. The drug decreases extrapyramidal symptoms, including akinesia, rigidity, tremors, excessive salivation, gait disturbances, and total functional disability. Well absorbed from GI tract. Peak blood levels: 4 hr. Onset: 48 hr. Peak serum concentration: 0.2 mcg/mL after 1-4 hr. t 1/2: Approximately 15 hr; elimination half-life increases two- to threefold when C CR is less than 40 mL/min/1.73 m 2. Renal clearance is reduced and plasma levels increased in otherwise healthy clients, aged 65 years and older. Ninety percent excreted unchanged in urine.
Influenza A viral infections of the respiratory tract (prophylaxis and treatment of high-risk clients with immunodeficiency, CV, metabolic, neuromuscular, or pulmonary disease). Symptomatic treatment of idiopathic parkinsonism and parkinsonism syndrome resulting from encephalitis, carbon monoxide intoxication, drugs, or cerebral arteriosclerosis. Favorable results have been obtained in about 50% of the clients. Improvements can last for up to 30 months, although some clients report that the effect of the drug wears off in 1-3 months. A rest period or an increased dosage may reestablish effectiveness. For parkinsonism, amantadine hydrochloride is usually used concomitantly with other agents, such as levodopa and anticholinergic agents.
Contraindications: Hypersensitivity to drug.
Special Concerns: Use with caution in clients with liver and renal disease, history of epilepsy, CHF, peripheral edema, orthostatic hypotension, recurrent eczematoid dermatitis, or severe psychosis, in clients taking CNS stimulant drugs, to those exposed to rubella, and to nursing mothers. Safe use in lactating mothers and in children less than 1 year has not been established.
Side Effects: GI: N&V, constipation, anorexia, xerostomia. CNS: Depression, psychosis, convulsions hallucinations, lightheadedness, confusion, ataxia, irritability, anxiety, headache, dizziness, fatigue, insomnia. CV: CHF orthostatic hypotension, peripheral edema. Miscellaneous: Urinary retention, leukopenia, neutropenia, mottling of skin of the extremities due to poor peripheral circulation (livedo reticularis), skin rashes, visual problems, slurred speech, oculogyric episodes, dyspnea, weakness, eczematoid dermatitis.
Overdose Management: Symptoms: Anorexia, N&V, CNS effects. Treatment: Gastric lavage or induction of emesis followed by supportive measures. Ensure that client is well hydrated; give IV fluids if necessary. To treat CNS toxicity: IV physostigmine, 1-2 mg given q 1-2 hr in adults or 0.5 mg at 5-10-min intervals (maximum of 2 mg/hr) in children. Sedatives and anticonvulsants may be given if needed; antiarrhythmics and vasopressors may also be required.
How Supplied: Capsule: 100 mg; Syrup: 50 mg/5 mL; Tablet: 100 mg