Health officials say antiviral resistance likely in some pandemic flu cases

Jun 30, 2009 (CIDRAP News) – A spokesman for Roche, the maker of oseltamivir (Tamiflu), said yesterday that Denmark's report of resistance to the drug in a patient with novel H1N1 (swine) influenza, the first reported finding of its kind, wasn't surprising and that the news underscores the importance of monitoring for any viral changes.

David Reddy, who leads Roche's influenza task force, told Bloomberg News that experts know that during seasonal influenza outbreaks, patients can develop resistance. "We fully expect that this can also occur during treatment with a new flu strain," he said.

He characterized what occurred in the Danish patient as "drug-induced resistance" that developed when a low dose of medication was used, as opposed to the more widespread resistance that occurs when a flu virus acquires new characteristics, which has happened over the past 2 years with the seasonal H1N1 strain.

World Health Organization (WHO) spokesman Dick Thompson said today that the Danish case is isolated and has no public health implications, Reuters reported. "But we must remain alert as the virus can change at any time and we must not be complacent," he added.

The antiviral resistance finding will not prompt any changes in the WHO antiviral recommendations, Thompson told Reuters.

Roche said it is monitoring drug resistance in several countries, and health officials in several nations, including the United States, are also watching for changes in the virus. The US Centers for Disease Control and Prevention (CDC) said in its most recent surveillance report, released Jun 24, that of 191 novel H1N1 isolates that have been tested for resistance to neuraminidase inhibitors, none showed resistance.

The CDC recommends treatment with oseltamivir or zanamivir for all patients who have confirmed, probable, or suspected novel H1N1 infections who are hospitalized or are at high risk for complications.

Carolyn Bridges, MD, associate director of epidemiologic science in the CDC's influenza division, told National Public Radio that though the United States hasn't detected any antiviral resistance in the new virus, it will likely occur here eventually. She said the novel flu virus has an "N1" gene that is very different than the "N1" of the seasonal H1N1 virus, so perhaps the pandemic virus isn't as susceptible to the antiviral resistance mutation seen with the seasonal H1N1 strain.

See also:

CDC influenza surveillance report for week ending Jun 20