Two people with compromised immune systems who became ill with 2009 H1N1 influenza developed drug-resistant strains of virus after less than 2 weeks on therapy, the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, doctors report.
Doctors who treat prolonged influenza infection should be aware that even a short course of antiviral treatment may lead to drug-resistant virus, said the authors, and clinicians should consider this possibility as they develop initial treatment strategies for their patients who have impaired immune function.
Both patients described in the new report developed resistance to the key influenza drug oseltamivir (Tamiflu), and one also demonstrated clinical resistance to another antiviral agent, now in experimental testing, intravenous peramivir, senior authors Matthew J. Memoli, MD, and Jeffery K. Taubenberger, MD, PhD, noted in a news release.
The people in the current case report had immune limitations due to blood stem cell transplants that occurred several years previously. Both recovered from their influenza infections.
“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,” NIAID director Anthony S. Fauci, MD, said. “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.”
The two people in the current case study had pre-existing medical conditions that impaired their immune system function before contracting 2009 H1N1 flu. Strains of 2009 H1N1 influenza containing the H275Y mutation had been reported previously in people with diminished immune function, but in previous cases the mutation arose after more than 24 days of continuous therapy. In the newly described cases, the mutation appeared after 14 days in one individual and after nine days in the second.
“Although the recommended length of treatment with oseltamivir is 5 days, it is common for physicians to continue giving this first-line drug longer if the patient does not improve,” Memoli said. “As clinicians, we should carefully consider our treatment options and use all the drugs available to us wisely. This is especially important in a patient with prolonged infection or when an antiviral drug fails to cure the patient after the recommended course of treatment.”