December 23rd, 2008

Flu Resistance to Oseltamivir: The Bugs Win Again

I must admit, the recent report that 49 of the 50 H1N1 flu viruses tested by the CDC are resistant to oseltamivir caught me by surprise.  For the non-math majors among the readership, that’s a 98% resistance rate.  Yikes.

Actually, the rate of resistance is so high that at first I didn’t believe it when my wife told me — thought she’d flipped the numbers.  “You mean that 1 of 50 was resistant,” I insisted — wrongly.  As usual, the pediatrician has the accurate news on the latest outbreak — I should have learned that long ago.

So … what happened?  Last year the resistance rate was only 10%, and it’s not as if since then we’ve put oseltamivir in the drinking water.  The bulk of people with influenza never get diagnosed or treated, so it can’t be due to excessive prescribing on the part of clinicians.  I doubt there’s much in the way of off-label or illicit use, and certainly nothing like this is showing up in my spam filter: 

Brand name T-A-M-I-F-L-U cheap!  From

One smart virologist I know suggested it might be the result of preventive programs in nursing home-type settings during flu outbreaks.  These preventive treatments can go on for weeks, so if the resistant viruses have any sort of evolutionary advantage, they could become the dominant strain. 

For now, interim guidelines for management of patients with influenza are available here.  We’ll be using zanamivir (must be the best name for an antiviral ever — too bad it can’t be used in kids or patients with asthma), and our old friend rimantadine — though this latter drug has no activity against influenza B, and of course H3N2 viruses are already likely to be resistant. 

Or we’ll be using nothing but TLC, which is kind of where we were several years ago.  And chalk another one up for the bugs, they are (in aggregate) pretty darn smart.

2 Responses to “Flu Resistance to Oseltamivir: The Bugs Win Again”

  1. arborvitae says:

    unn err dr sax. with 2.5 billion chinese ducks receiving tamiflu in their feed on a daily basis for the last 3 years, ya think that might have had a greater influence on viral resistance than grandma mary’s week in november?

  2. Paul Sax says:

    I see your point, and agree that it’s highly unlikely that a few thousand “Grandma Mary’s” are engendering this rate of resistance.

    Is there oseltamivir in duck feed? I had no idea …

    But I did find this prescient post:

HIV Information: Author Paul Sax, M.D.

Paul E. Sax, MD

Contributing Editor

NEJM Journal Watch
Infectious Diseases

Biography | Disclosures | Summaries

Learn more about HIV and ID Observations.