Use of Anti-Viral Drugs for Treatment of Influenza

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Flu Treatment

Recent, additional data show that the prevalence of adamantane-resistant influenza A viruses is high across the United States, according to a new study published online today by JAMA because of its public health importance. The study will be in the February 22 print issue of JAMA.

On Jan. 14, 2006, the Centers for Disease Control and Prevention (CDC) issued a Health Alert recommending that certain anti-viral drugs, specifically amantadine and rimantadine should not be used for treatment or prevention of influenza A infections in the United States for the remainder of the 2005 - 2006 influenza season. This recommendation was based on 120 influenza A viruses isolated from patients in 23 states.

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Amantadine and rimantadine are in a class of drugs called adamantanes and have been used as a first-choice antiviral drug against community outbreaks of influenza A viruses for many years. According to the authors of the current JAMA study, rates of viruses resistant to these drugs have been increasing globally and rapid surveillance for the emergence and spread of resistant viruses is critical for the treatment of patients. The authors write that on average, influenza A viruses, a major cause of illness and death in the U.S., infect about 10 - 15 percent of the population annually. While vaccination is the primary strategy for preventing influenza infections, influenza antiviral drug therapy (such as amantadine and rimantadine) is effective for treating patients with the flu, especially in nursing homes and long term care facilities.

Rick A. Bright, Ph.D., and colleagues from the CDC, Atlanta, analyzed 209 influenza isolates collected from patients in 26 states from Oct. 1 through Dec. 31, 2005, and tested for drug resistance as part of ongoing surveillance. "Of the 209 A (H3N2) viruses screened, we found an alarmingly high adamantane resistance rate of 92 percent," the researchers report. "These viruses were isolated from patients residing in 26 states, representing all regions of the United States. This rate was much higher than the rate found among viruses collected within the United States during previous influenza seasons."

"Our results highlight the importance of continued surveillance for the emergence and transmission of influenza viruses resistant to antiviral drugs. They serve as a warning to the medical community of the speed at which resistant influenza viruses can become predominant circulating strains and spread throughout a continent," the authors conclude. (JAMA. 2006)

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