Amantadine is a synthetic antiviral agent that also has strong antiparkinsonian properties. It is sold in the United States under the brand name Symmetrel, and is also available under its generic name.
Amantadine is used to treat a group of side effects, called parkinsonian side effects, that include tremors, difficulty walking, and slack muscle tone. These side effects may occur in patients who are taking antipsychotic medications used to treat mental disorders such as schizophrenia. An unrelated use of amantadine is in the treatment of viral infections of some strains of influenza A.
Some medicines, called antipsychotic drugs, that are used to treat schizophrenia and other mental disorders can cause side effects similar to the symptoms of Parkinson's disease. The patient does not have Parkinson's disease, but may experience shaking in muscles while at rest, difficulty with voluntary movements, and poor muscle tone. These symptoms are similar to the symptoms of Parkinson's disease.
One way to eliminate these undesirable side effects is to stop taking the antipsychotic medicine. Unfortunately, the symptoms of the original mental disorder usually come back; in most cases, simply stopping the antipsychotic medication is not a reasonable option. Some drugs such as amantadine that control the symptoms of Parkinson's disease also control the parkinsonian side effects of antipsychotic medicines.
Amantadine works by restoring the chemical balance between dopamine and acetylcholine, two neurotransmitter chemicals in the brain. Taking amantadine along with the antipsychotic medicine helps to control symptoms of the mental disorder, while reducing parkinsonian side effects. Amantadine is in the same family of drugs commonly known as anticholinergic drugs, including biperiden and trihexyphenidyl.
Amantadine is available in 100 mg tablets and capsules, as well as a syrup containing 50 mg of amantadine in each teaspoonful. For the treatment of drug-induced parkinsonian side effects, amantadine is usually given in a dose of 100 mg orally twice a day. Some patients may need a total daily dose as high as 300 mg. Patients who are taking other antiparkinsonian drugs at the same time may require lower daily doses of amantadine (e.g., 100 mg daily).
Amantadine increases the amount of the dopamine (a central nervous system stimulant) in the brain. Because of this, patients with a history of epilepsy or other seizure disorders should be carefully monitored while taking this drug. This is especially true in the elderly and in patients with kidney disease. Amantadine may cause visual disturbances and affect mental alertness and coordination. People should not operate dangerous machinery or motor vehicles while taking this drug.
Five to 10% of patients taking amantadine may experience nervous system side effects, including:
- dizziness or lightheadedness
- nervousness or anxiety
- impaired concentration
One to 5% of patients taking amantadine may experience other nervous system side effects, including:
- irritability or agitation
- lack of coordination
- sleepiness or nightmares
In addition, up to 1% of patients may experience hallucinations, euphoria (excitement), extreme forgetfulness, aggressive behavior, personality changes, or seizures. Seizures are the most serious of all the side effects associated with amantadine.
Gastrointestinal side effects may also occur in patients taking amantadine. Five to 10% of people taking this drug experience nausea and up to 5% have dry mouth, loss of appetite, constipation, and vomiting. In most situations, amantadine may be continued and these side effects treated symptomatically.
One to 5% of patients taking amantadine have also reported a bluish coloring of their skin (usually on the legs) that is associated with enlargement of the blood vessels (livedo reticularis). This side effect usually appears within one month to one year of starting the drug and subsides within weeks to months after the drug is discontinued. People who think they may be experiencing this or other side effects from any medication should tell their physician.
Taking amantadine along with other drugs used to treat parkinsonian side effects may cause increased confusion or even hallucinations. The combination of amantadine and central nervous system stimulants (e.g., amphetamines or decongestants) may cause increased central nervous stimulation or increase the likelihood of seizures.
American Society of Health-System Pharmacists. AHFS Drug Information 2002. Bethesda: American Society of Health-System Pharmacists, 2002.
DeVane, C. Lindsay, PharmD. "Drug Therapy for Psychoses." In Fundamentals of Monitoring Psychoactive Drug Therapy. Baltimore: Williams and Wilkins, 1990.
Jack Raber, PharmD