Clinical evidence of oseltamivir (Tamiflu, Roche) resistance has been confirmed in patients infected with the novel avian H7N9 flu, as published online in The Lancet.

A case series was conducted in 14 patients with influenza A H7N9 disease admitted to the Shanghai Public Health Clinical Centre. Patients were given either oseltamivir or peramivir for <2 days prior to admission. Researchers sequenced viral RNA from throat, stool, serum, and urine specimens to study the mutations associated with resistance to neuraminidase inhibitors and their association with disease outcome.

All 14 patients developed pneumonia, and seven of them required mechanical ventilation. For 11 out of 14 patients, antiviral treatment lowered the viral load on throat swabs. However, the three patients developed severe illness that required extracorporeal membrane oxygenation (ECMO), and two patients died.

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According to Chinese researchers, an Arg292Lys mutation in the virus neuraminidase (NA) gene known to confer resistance to both zanamivir (Relenza; GlaxoSmithKline) and oseltamivir was identified in two of these patients – both also received corticosteroid treatment. In one of them, wild-type sequence Arg292 was noted two days after start of antiviral treatment, and the resistant mutant Lys292 dominated 9 days after start of treatment.

Researchers concluded that the emergence of antiviral resistance in avian H7N9 viruses, especially in patients receiving corticosteroid therapy, “is concerning, needs to be closely monitored, and considered in pandemic preparedness planning.”


  1. Hu Y et al. Lancet. 2013; doi:10.1016/S0140-6736(13)61125-3.

This article originally appeared on MPR