New flu drug can trigger resistance in influenza viruses

New flu drug can trigger resistance in influenza viruses

Roche’s influenza treatment Xofluza may cause a mutation of the virus that leads to drug resistance, researchers clain, Reuters reports.


Xofluza is a one-dose pill that can clear flu symptoms within days.


The antiviral won U.S. approval last year to treat people 12 and older, and earlier this month was approved for patients at high risk of flu complications.


The Swiss drugmaker is seeking to establish Xofluza as a more convenient alternative to its older Tamiflu, which is taken twice daily for five days and is facing competition from cheaper generics.


A single mutation resistant to baloxavir


The study was published in Nature Microbiology by researchers at the University of Wisconsin-Madison. It analysed involved flu samples from an 11-year old boy in Japan diagnosed with the flu last January and treated with the drug, known chemically as baloxavir. Although he improved initially, the boy’s fever returned, and two days later, his 3-year-old sister was diagnosed with the flu.


The Wisconsin team, led by flu expert Yoshihiro Kawaoka, sequenced DNA of flu samples from the siblings and found the girl’s virus harbored a single mutation resistant to baloxavir.

Results of the study suggest that common flu strains can quickly acquire resistance to the drug. They caution patients who receive it - especially children - should be watched for drug resistance.


Drug resistance to H1N1 or H3N2 strains


Kawaoka said prior studies had also found drug resistance, which led him to study resistance in larger groups of patients exposed to H1N1 or H3N2, two common flu strains.


For H1N1, the team tested 74 samples from infected patients before treatment and 22 samples from patients both before and after treatment. They found no mutations in any of the samples before treatment, but 23% of patients carried drug-resistant mutations after treatment.


Although it is unlikely baloxavir will cause widespread resistance, Kawaoka said it could be a problem when infected patients are in close proximity.


Patients with H1N1 or H3N2 who develop resistance to baloxavir treatment do respond to other virus-fighting drugs, he said.