Amantadine

Treatment with oral amantadine or rimantadine begun within 48 hours after the onset of illness decreases the duration of fever and symptoms by about 1 day. Whether these drugs decrease influenza-related complications or are effective in treating severe influen-za pneumonia is unknown. Neither amantadine nor rimantadine is effective against influenza B virus.

Either amantadine or rimantadine is 70% to 90% effective in preventing influenza A when started before exposure. Prophylaxis with amantadine or rimantadine has been used to control institutional influenza outbreaks and to protect high-risk patients immunized after or <2 weeks before an epidemic has begun. The drugs can also be used as prophylaxis for immunodeficient patients who may respond poorly to influenza vaccine, and in unvaccinated persons who are at high risk for influenza or are caring for high-risk patients.