British doctors have saved the life of a woman with severe swine flu after giving her an unlicensed intravenous form of GlaxoSmithKline's drug Relenza, they reported today.

Relenza, or zanamivir, is currently only approved as an inhaled medicine. This version, however, did not work in the 22-year-old patient, whose immune system was impaired due to recent chemotherapy.

She also did not respond to Roche's Tamiflu, or oseltamivir, which is given as a pill.

Doctors at University College London therefore decided to try intravenous Relenza in combination with high-dose corticosteroids and her condition improved within 48 hours.

"Although this is a single case report and direct cause and effect cannot be confirmed, the improvement in clinical status following intravenous Relenza encourages prompt further investigation," Michael Kidd and Mervyn Singer reported.

The new H1N1 swine flu was declared a pandemic in June and has been spreading globally since then.

Other flu drugs are under development to deal with seasonal and pandemic influenza. One that has shown promise in intravenous form is BioCryst Pharmaceuticals's experimental product peramivir.