Amantadine hydrochloride
Amantadine hydrochloride (Symmetrel)
Amantadine hydrochloride
(ah- MAN-tah-deen)
Pregnancy Category: C Endantadine Gen-Amantadine PMS-Amantadine Symadine Symmetrel (Rx)

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.

Uses: 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.
Amantadine is recommended for prophylaxis in the following situations: Short-term prophylaxis during the course of a presumed outbreak of influenza A Adjunct to late immunization in high-risk clients To reduce disruption of medical care and to decrease spread of virus in high-risk clients when influenza A virus outbreaks occur To supplement vaccination protection in clients with impaired immune responses As chemoprophylaxis during flu season for those high-risk clients for whom influenza vaccine is contraindicated due to anaphylactic response to egg protein or prior severe reactions associated with flu vaccination

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.

Drug Interactions: Anticholinergics / Additive anticholinergic effects (including hallucinations, confusion), especially with trihexyphenidyl and benztropine Belladonna leaf/root / Anticholinergic effect CNS stimulants / May CNS and psychic effects of amantadine; use cautiously together Henbane leaf / Anticholinergic effects Hydrochlorothiazide/triamterene combination / Urinary excretion of amantadine plasma levels Levodopa / Potentiated by amantadine Pheasant's eye herb / Amantadine effect Scopolia root / Amantadine effect

How Supplied: Capsule: 100 mg; Syrup: 50 mg/5 mL; Tablet: 100 mg

Dosage
?Capsules, Syrup Antiviral.
Adults: 200 mg/day as a single or divided dose. Children, 1-9 years: 4.4-8.8 mg/kg/day up to a maximum of 150 mg/day in one or two divided doses (use syrup); 9-12 years: 100 mg b.i.d.
Prophylactic treatment.
Institute before or immediately after exposure and continue for 10-21 days if used concurrently with vaccine or for 90 days without vaccine.
Symptomatic management.
Initiate as soon as possible and continue for 24-48 hr after disappearance of symptoms. Decrease dose in renal impairment (see package insert). Reduce dose to 100 mg/day for persons with active seizure disorders due to the increased risk of seizure frequency using daily doses of 200 mg.
Parkinsonism.
Use as sole agent, usual: 100 mg b.i.d., up to 400 mg/day in divided doses, if necesssary. Use with other antiparkinson drugs: 100 mg 1-2 times/day.
Drug-induced extrapyramidal symptoms.
100 mg b.i.d. (up to 300 mg/day may be required in some). Reduce dose in impaired renal function.