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amantadine, Symmetrel

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GENERIC NAME: amantadine

BRAND NAME: Symmetrel

DRUG CLASS AND MECHANISM: Amantadine is a synthetic (man-made) anti-viral drug that can inhibit the replication of viruses in cells. To prevent a viral infection, the drug should be present before exposure to the virus. Clearly, this is not practical for most viral infections. It was initially used to prevent influenza A during flu season, and, if given within 24 to 48 hours of the onset of flu symptoms, to decrease the severity of the flu. Later amantadine was found to cause improvement in the symptoms of Parkinson's disease. Amantadine's mechanism of action in Parkinson's disease is not fully understood. Its effects may be related to its ability to augment (amplify) the effects of dopamine, a neurotransmitter in the brain, that is reduced in Parkinson's disease. Amantadine is less effective than levodopa in Parkinson's disease but can offer additional benefit when taken with levodopa. Amantadine was approved by the FDA in 1966.

GENERIC AVAILABLE: yes

PRESCRIPTION: yes

PREPARATIONS: Amantadine is available as 100mg soft gelatin capsules and as a syrup containing 50mg per each teaspoon.

STORAGE: Store at room temperature between 15 and 30°C (59 and 86°F).

PRESCRIBED FOR: Amantadine is used for the prevention or treatment of infections with influenza A virus, especially for individuals at high-risk such as immunosuppressed patients and nursing home residents. It should not be used as a substitute for vaccination. Amantadine also is used for control of the symptoms of Parkinson's disease.

DOSING: Amantadine is taken once or twice daily with or without food. If it causes an upset stomach, it can be taken with food.

For treatment of influenza, amantadine should be started within 24 to 48 hours after the onset of signs or symptoms and should be continued for 24 to 48 hours after the disappearance of signs or symptoms. To prevent influenza, amantadine should be started as soon as possible after exposure to the influenza virus and continued for at least 10 days.

Persons with reduced kidney function and elderly persons may need lower doses (or less frequent doses).

DRUG INTERACTIONS: Amantadine adds to the sedating effects alcohol and other sedating drugs such as the benzodiazepine class of anti-anxiety drugs (e.g., Valium, Ativan, Klonopin, Xanax, Ambien), the tricyclic class of antidepressants (e.g., Elavil, Tofranil, Norpramin), dicyclomine (Bentyl), certain antihistamines (Benadryl, Vistaril, Atarax, Tavist), opiate agonists (e.g., Dilaudid; Vicodin; Percocet; Codeine) and certain antihypertensive medications (e.g., Catapres, Inderal). Such combinations can cause dizziness, confusion, lightheadedness, fainting, or dizziness upon standing.

Since amantadine amplifies the actions of dopamine in the brain, drugs which block the effects of dopamine should be avoided in persons taking amantadine when amantadine is used for the treatment of Parkinson's disease. Such drugs include haloperidol (Haldol), metoclopramide (Reglan), and phenothiazines, e.g., thioridazine (Mellaril) or triflupromazine (Stelazine).

The use of the diuretics hydrochlorothiazide or triamterene (Dyazide; Maxzide) with amantadine can reduce the kidney's ability to eliminate amantadine. This can lead to high levels of amantadine in the blood and amantadine-associated toxicity.

PREGNANCY: No well-controlled studies have been done in pregnant women to evaluate amantadine's safety. Physicians may choose to use amantadine during pregnancy when the potential benefits outweigh the potential but unknown risks to the fetus.

NURSING MOTHERS: Amantadine is excreted into breast milk in low concentrations. Although no information is available on the effects in infants, the manufacturer recommends that amantadine be used cautiously in nursing mothers.

SIDE EFFECTS: The most frequent side effects associated with amantadine include dizziness, loss of coordination, inability to sleep, and nervousness, nausea, and vomiting. All of these side effects have been reported to occur in about 1 in 20 persons. Effects can appear after a few hours or several days of therapy. Less common side effects include headache, irritability, nightmares, depression, confusion, drowsiness, and hallucinations, weakness, amnesia, slurred speech, diarrhea, constipation, and loss of appetite, and discolorations in the eye.

Reference: FDA Prescribing Information

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