Implications of viral resistance to amantadine in control of influenza A.

Antiviral agents are valuable adjuncts to vaccine in the control of type A influenza. Amantadine has been available for many years for prophylaxis and therapy, but there have been concerns about side effects, particularly in the elderly. Thus, the anticipated licensure of rimantadine, an antiviral with the same efficacy as amantadine but with fewer side effects, has been viewed as a major advance. Rimantadine has thus far remained unlicensed, and attention has become focused on antiviral resistance to these drugs, an issue previously recognized but not considered important in decisions concerning drug use. The major implications of antiviral resistance relate to questions of whether there are differences in pathogenicity and transmissibility of resistant influenza type A viruses in comparison with sensitive ones. Resistant viruses have not been found to be more virulent than sensitive ones. The extent to which they may be transmitted or perpetuated has not been established. In light of this situation, it is suggested that drug use not be sharply restricted and that recommendations be periodically reviewed as more definitive data become available. As with any infectious disease, attempts should be made to limit exposure of uninfected individuals to those infected with the influenza A virus, regardless of whether they are receiving an antiviral drug.