Adamantanes have been used to treat inﬂuenza A virus infections for more than 30 years. Previous surveillance studies have identiﬁed a low incidence of resistance to amantadine and rimantadine among circulating inﬂuenza virus strains. However, it has been 10 years since the last comprehensive global study of resistance to these drugs was published.
In the largest study of adamantane resistance to date, researchers from Centers for Disease Control and Prevention, Atlanta, USA had screened 7000 inﬂuenza A isolates for gene mutations known to confer drug resistance. They found that drug resistance increased from 0·4% in 1994-1995 to 12.3% in 2003-2004. They also found that 61% of resistant viruses isolated since 2003 were from people in Asia. Some Asian countries had drug resistance frequencies exceeding 70%.
The researchers were alarmed to ﬁnd such a dramatic increase in drug resistance in circulating human inﬂuenza viruses in recent years. Their report has broad implications for agencies and governments planning to stockpile these drugs for epidemic and pandemic strains of inﬂuenza. With the increasing rates of resistance shown there, amantadine and rimantadine will probably no longer be effective for treatment or prophylaxis in the event of a pandemic outbreak of inﬂuenza, said the researchers for the study.
Source: Newswise, The Lancet