amantadine, Symmetrel (Discontinued): Side Effects, Uses, Dosage

What is amantadine, and how does it work (mechanism of action)?

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.

Is amantadine available as a generic drug?

GENERIC AVAILABLE: No

Do I need a prescription for amantadine?

Yes

What are the uses for amantadine?

Amantadine is prescribed for the prevention and treatment of infections with influenza A. Amantadine is also prescribed to control the symptoms of Parkinson's disease and for the treatment of drug-induced extrapyramidal symptoms.

What are the side effects of amantadine?

The most frequent side effects associated with amantadine that can appear after a few hours or several days of therapy include:

• dizziness,
• loss of coordination,
• inability to sleep,
• nervousness,
• nausea, and
• vomiting.

Less common side effects include:

• headache,
• irritability,
• nightmares,
• depression,
• confusion,
• drowsiness,
• hallucinations,
• weakness,
• amnesia,
• slurred speech,
• diarrhea,
• constipation,
• loss of appetite, and
• discolorations in the eye.

What is the dosage for amantadine?

Amantadine is taken once or twice daily with or without food. If it causes an upset stomach, it can be taken with food. The dosage for prevention and treatment of influenza A infections in adults is 200 mg daily. 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).

The dosage for treating Parkinson's or extrapyramidal symptoms is 100 mg twice daily.

Which drugs or supplements interact with amantadine?

Amantadine adds to the sedating effects of alcohol and other sedating drugs such as:

• The benzodiazepine class of anti-anxiety drugs, for example:
  • diazepam (Valium)
  • lorazepam (Ativan)
  • clonazepam (Klonopin)
  • alprazolam (Xanax, Xanax XR, Niravam)
  • zolpidem (Ambien, Ambien CR, Zolpimist, Edluar)
• The tricyclic class of antidepressants, for example:
  • amitriptyline (Elavil, Endep)
  • imipramine (Tofranil, Tofranil-PM)
  • desipramine (Norpramin)
• dicyclomine (Bentyl)
• Certain antihistamines, for example:
  • diphenhydramine (Benadryl)
  • hydroxyzine (Vistaril, Atarax)
  • clemastine
• Opiate agonists, for example:
  • hydromorphone hydrochloride (Dilaudid)
  • hydrocodone/acetaminophen (Vicodin, Vicodin ES, Lorcet, Lorcet Plus, Norco)
  • oxycodone and acetaminophen (Percocet, Roxicet, Tylox, Oxycet)
  • codeine
• Certain antihypertensive medications, for example:
  • clonidine (Catapres, Catapres-TTS, Jenloga)
  • propranolol (Inderal, Inderal LA, Innopran XL)

Such combinations can cause dizziness, confusion, lightheadedness, fainting, or dizziness upon standing (orthostatic hypotension).

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, for example, 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.

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Is amantadine safe to take if I’m pregnant or breastfeeding?

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.

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 women who are breastfeeding.

What else should I know about amantadine?

What preparations of amantadine are available?

Capsule: 100 mg. Syrup: 50 mg/5 ml (teaspoon).

How should I keep amantadine stored?

Amantadine should be stored at room temperature between 15 C – 30 C (59 F – 86 F).