WASHINGTON, March 26 The H1N1 swine flu virus
can develop resistance quickly to antivirals used to treat it,
U.S. doctors reported on Friday.
Government researchers reported on the cases of two people
with compromised immune systems who developed drug-resistant
strains of virus after less than two weeks on therapy.
Bacteria quickly develop resistance to antibiotics, which
must be used carefully. Viruses can do the same and doctors
worried about resistance had recommended against using
antivirals for 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," he said in a statement.
Swine flu emerged a year ago in the United States and
Mexico and spread around the world in just six weeks, killing
thousands of people. It hit children and young adults
Older antiviral drugs did not work against it -- they do
not work against seasonal flu, either -- but Roche AG's
Tamiflu, known generically as oseltamivir, did. It was not
widely used, however.
Dr. Jeffery Taubenberger and colleagues studied two flu
patients who had immune limitations due to past blood stem cell
transplants. They were treated with Tamiflu.
Writing in the journal Clinical Infectious Diseases,
Taubenberger and colleague Dr. Matthew Memoli said the virus
infecting one patient developed a drug-resistant mutation after
nine days and the other after 14 days of treatment.
And one of the patients also developed resistance against a
second antiviral, Biocryst's (BCRX.O) peramivir, which is an
experimental drug approved for emergency intravenous use in
patients who cannot take Tamiflu.
This patient continued getting worse depsite 24 days on
Tamiflu and was given peramivir for 10 days.
Finally, GlaxoSmithkline's (GSK.L) flu drug Relenza, known
generically as zanamivir, did work and the patient recovered,
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.