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Evidence for resistance to Tamiflu grows

By Mark Pownall

Swine flu resistant to the antiviral drug oseltamivir has been identified by doctors caring for a family hit by the infection in Canada.

The discovery follows the identification of a small number of patients at the University Hospital Wales, in Cardiff, with a Tamiflu-resistant swine flu infection last month.

The Canadian resistant strain of the virus was 400 times less sensitive to the neuraminidase inhibitor than the wild type of the virus, according to the Quebecois doctors in a letter to the New England Journal of Medicine. It remained sensitive to zanamivir (Relenza).

The resistant virus had a single amino acid change - H275Y mutation - of its neuraminidase protein, identical to a change that has caused widespread Tamiflu resistance in recent seasonal H1N1 flu viruses. The researchers point to a WHO statement that it has received reports of several dozen cases of swine flu resistant to Tamiflu.

Lead researcher Dr Mariana Baz from the University Hospital of Quebec said: ‘These observations support the need for limiting the indications for post-exposure prophylaxis. It also seems reasonable to rapidly convert prophylactic once daily regimens to therapeutic twice daily regimens as soon as influenza-like symptoms develop in patients receiving prophylaxis.'

New England Journal of Medicine, published online November 11, 2009

Swine flu resistant to Tamiflu has been identified by doctors in Quebec

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