MARIA CHENG AP Medical Writer LONDON (AP) — A new and unlicensed treatment for swine flu could be used in patients who have Tamiflu-resistant viruses, doctors say. In an article published Friday in the medical journal Lancet, British doctors describe how they used an intravenous form of the antiviral Relenza to treat a 22-year-old woman who had a severe case of swine flu. Relenza is usually inhaled via the nose, and is not licensed to be given intravenously. The woman had recently undergone chemotherapy for Hodgkin's disease. After catching swine flu, her lungs filled with fluid and she was put on a ventilator to help her breathe. Despite days of being given Tamiflu, inhalable Relenza, and other medicines, the patient deteriorated. So her doctors decided to try a different way of getting the drug into her body, since her lungs weren't able to absorb the antivirals the usual way. After getting permission from her family and a hospital committee, they gave her an unlicensed, intravenous form of the antiviral zanamivir, or Relenza, provided by its maker, GlaxoSmithKline PLC. The patient recovered soon afterward, with no reported side effects. "This may provide a third route to treat patients that are not responding to antiviral treatment because the active drug is not getting to the lungs," said Michael Kidd, of University College London, and the lead author of the study. "Although we now know our patient did not have Tamiflu-resistant virus, the intravenous zanamivir could potentially be used to treat such a case," Kidd said. The World Health Organization said the treatment was likely to be used only in rare circumstances, since it is not easily available and is unlicensed. But in patients with weak immune systems — like those who have had chemotherapy or have diseases like HIV — the treatment may be useful since they are at high risk of developing drug-resistant viruses."To change the antiviral being used is therefore a logical option in those cases," said Gregory Hartl, a WHO spokesman. Tamiflu, made by Switzerland's Roche Group, is usually the first treatment for swine flu, though GlaxoSmithKline's Relenza is occasionally used.Only a handful of Tamiflu-resistant swine flu viruses have been picked up so far, but the virus could mutate into a resistant form the more it spreads. Widespread Tamiflu resistance has been seen in a seasonal strain of H1N1, distantly related to swine flu.Countries which give out Tamiflu liberally, like Britain, might also speed up the emergence of resistant viruses.Contrary to WHO recommendations, which suggests Tamiflu be saved for vulnerable groups like pregnant women and children, Britain gives out Tamiflu to anyone thought to have the virus.Call center workers without any medical training at its national flu hot line gave out tens of thousands of doses of the drugs to otherwise healthy people who had swine flu this summer.Kidd said the intravenous Relenza might also be useful to treat other severely ill patients with flu, and could potentially shorten their stay in the hospital. That might relieve the anticipated crush on hospital beds in the coming winter season, when swine flu is expected to rebound.A similar case of using Relenza intravenously was reported in Australia in a patient who also survived a serious bout of swine flu.Countries in the northern hemisphere are now making last-minute preparations for the imminent flu season, since a vaccine is not expected to be available before mid-October at the earliest.Even though the swine flu virus is mild, the numbers of people who catch the virus — WHO has estimated 2 billion people worldwide could be infected — could overwhelm health systems.