Rimantidine amantidine use and toxicity

These drugs are prophylactic against influenza A virus infection and can reduce the duration of symptoms if given within 48 h after contact.However, adamantine-resistant influenza A virus mutants including H3N2 strains causing seasonal influenza in the United States have increased dramatically in the last 2–3 yr. The H1N1 strain responsible for the recent pandemic that contain genes derived from both avian and porcine influenza viruses is also resistant to the adamantines. Fortunately, there is minimal cross-resistance to the neuraminidase inhibitors. Neither impairs the immune response to influenza A vaccine, and either can be administered as a supplement to vaccination, thus providing protection until antibody response occurs (usually 2 weeks in healthy adults). Treatment is particularly useful in high-risk patients who have not been vaccinated and during epidemics. [Note: Amantadine is also effective in the treatment of some cases of Parkinson disease.] Toxic effects of these agents include GI irritation, dizziness, ataxia, and slurred speech. Rimantadine’s activity is no greater than that of amantadine, but it has a longer half-life and requires no dosage adjustment in renal failure.The side effects of amantadine are mainly associated with the CNS. Minor neurologic symptoms include insomnia,dizziness, and ataxia. More serious side effects have been reported(for example, hallucinations and seizures). The drug should be employed cautiously in patients with psychiatric problems, cerebral atherosclerosis, renal impairment, or epilepsy. Rimantadine causes fewer CNS reactions, because it does not efficiently cross the blood-brain barrier. Both drugs cause GI intolerance.Amantadine and rimantadine should be used with caution in pregnant and nursing mothers, because they have been found to be embryotoxic and teratogenic in rats.