TAMIFLU (TAM-ih-flew) is a medicine to treat flu (infection caused by influenza virus). It belongs to a group of medicines called neuraminidase inhibitors. These medications attack the influenza virus and prevent it from spreading inside your body.

New doubts about the efficacy of Tamiflu as a treatment for bird flu were raised on Wednesday when a leading medical journal published new reports of resistance to the drug and deaths in patients in Vietnam.

Menno de Jong and colleagues from the hospital for tropical diseases in Ho Chi Minh City outlines in the New England Journal of Medicine how four out of eight patients suffering from the H5N1 flu strain and treated with Tamiflu had died, including two who developed resistance.

The reports indicate increased levels of resistance to nearly 10 per cent, or three out of the 31 known human cases of H5N1 treated with Tamiflu, which is produced by drugs firm Roche of Switzerland.

The study raises concerns about the drug, which many governments have ordered in large quantities in recent months to stockpile as a potential prophylactic and treatment in the case of a flu pandemic.

Another article in the Journal reinforced calls for alternative approaches to treatment for a pandemic, including the stockpiling of the rival drug zanamivir, or Relenza.

Dr Anne Moscona wrote that individuals’ stockpiling of Tamiflu was “potentially dangerous” because it could lead to insufficient doses and inadequate courses of therapy, in turn accelerating the development of resistance.

TAMIFLU is a neuraminidase (noor-uh-MIN-ih-dase) inhibitor. These inhibitors treat the cause of influenza infection by inhibiting the critical neuraminidase protein on the surface of the virus. As the flu multiplies, neuraminidase enables it to move on and infect other host cells (left). When you inhibit neuraminidase (right), the flu can't escape from its host cell, which prevents it from spreading.

Roche is reported to have said that it took the reports seriously, and was stepping up its own clinical research on Tamiflu’s use in humans and animals, including work on dosages of twice the current levels for longer periods. It said findings should be ready early next year.

David Reddy, who is responsible for Tamiflu at Roche, stressed that any findings on resistance or deaths should be set against the fact that an eventual pandemic strain of H5N1 would be different from the current bird flu virus which has so far infected 139 people and killed 71.

Oseltamivir Resistance during Treatment of Influenza A (H5N1) Infection

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