U.S. doctors reported on Friday that the H1N1 swine flu virus can develop resistance to antivirus treatments very quickly.
Government researchers reported cases of two persons with compromised immune systems who developed new strains of the virus after less than two weeks of therapy. The new strains are showing resistance to the antiviral drugs.
Bacteria develop resistance to antibiotics quickly, which must be treated carefully. Viruses can do the same and doctors recommended that antiviral drugs not be used against the flu except in patients who really needed them.
“While the emergence of drug-resistant influenza virus is not in itself surprising, these cases demonstrate that resistant strains can emerge after only a brief period of drug therapy,” said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, “We have a limited number of drugs available for treating influenza and these findings provide additional urgency to efforts to develop antivirals that attack influenza virus in novel ways,” Fauci told Reuters.
Swine flu emerged just over a year ago and spread worldwide in just six weeks, killing thousands of people. Children and young adults were the hardest hit. Older antiviral vaccines did not work against it — they also did not work against seasonal flu — but Tamiflu, made by Roche AG, did. It was not widely used, however.
Researchers studied two flu patients who had weakened immune systems due to past blood stem cell transplants. Both were treated with Tamiflu. Dr. Jeffrey Taubenberger and Dr. Matthew Memoli, who worked with the patients, and wrote about the studies in the journal Clinical Infectious Diseases, said the virus in one patient developed a drug-resistant mutation after nine days of treatment and the other after 14 days of treatment.
They said one of the patients also developed resistance against a second experimental antiviral drug, peramivir, which has been approved for emergency intravenous use in patients who cannot take Tamiflu. The patient continued to get worse after being on Tamiflu for 24 days and peramivir for an additional 10 days. The patient finally recovered after receiving the flu drug Relenza, manufactured by GlaxoSmithKline, the researchers said.
“These cases of rapid appearance of drug-resistant 2009 H1N1 influenza in immune-compromised patients are worrisome and should prompt clinicians to reconsider how they use available flu drugs,” Memoli said.
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