The Centers for Disease Control and Prevention (CDC) announced today that clinicians should not prescribe two common antivirals (amantadine and rimantadine) to treat or prevent influenza during the 2005-2006 influenza season.Â Laboratory testing by CDC on the predominant strain of influenza (H3N2) currently circulating in the United States shows that it is resistant to these drugs.
The CDC has tested 120 influenza A (H3N2) virus isolates and found that 109 (or 91 percent) were resistant to amantadine and rimantadine.Â This represents a sharp increase from last year when only 11 percent of isolates tested were resistant and 1.9 percent were resistant the year before that.Â However, all H3 and H1 influenza viruses tested to date are susceptible to the other commonly used antivirals (oseltamivir and zanamivir).
"This is certainly unexpected news as we now have to remove a few tools from our tool box that we use to combat influenza," said CDC Director Julie Gerberding, MD, MPH. "Thankfully we still have antivirals available that work but this new development serves as a reminder of the importance of getting people vaccinated to prevent them from getting influenza in the first place."
During this period the CDC recommends oseltamivir (Tamiflu) and zanamivir (Relenza) be prescribed if an antiviral medication is needed for the treatment or prevention of influenza.Â
Influenza activity is starting to pick up across the country, as 18 states are reporting either widespread or regional activity. Individuals who have not been vaccinated against influenza can still get vaccinated especially since influenza will continue to circulate for several more months.Â This year, more than 80 million doses of vaccine have been distributed but remaining supplies vary from state to state so individuals may have to check with more than one provider to receive vaccine.Â Also, the CDC will have available 3.5 million doses from its stockpile to sell through manufacturers as soon as possible.Â In addition there are doses of vaccine presently available for sale by manufacturers and distributors.Â
Testing of influenza isolates for resistance to antivirals will continue throughout the 2005-2006 influenza season and recommendations will be updated as needed.Â In addition, the CDC is working with state and local health departments and clinicians across the country to monitor drug resistance in influenza viruses.