London

The UK government agreed last week that physicians should be discouraged from prescribing a novel anti-viral drug, Relenza, on the grounds that it is not convinced of the drug's cost-effectiveness.

The government's announcement endorsed advice to physicians from the newly created National Institute of Clinical Excellence (NICE), set up to provide guidance on whether new therapies should be introduced into the health service.

But Glaxo Wellcome — maker of Relenza — and two other leading pharmaceutical companies want the government to reverse its decision and overrule NICE. They argue that the need to obtain the institute's approval is anti-innovative and an unjustifiable additional hurdle for new drugs to overcome.

Relenza prevents the spread of the virus to uninfected cells in the respiratory tract. It is the first in a class of compounds known as neuraminidase inhibitors, and the first anti-viral drug to be effective against all known strains of influenza A and B.

For influenza to spread, new virus particles must break out from infected cells. The enzyme neuraminidase breaks the bond holding the virus to the infected cell. Relenza inhibits neuraminidase activity, so retaining the bonds between sialic acid and cell surface proteins, and trapping the virus in sugars on the outside of the cell.

The influenza virus is highly mutable, and comes in many different strains. This has made it difficult to locate a stable target to prevent viral replication. After three decades, researchers discovered that the role of neuraminidase is constant. Once this had been identified, Relenza was designed using computational chemistry.

Persuading the government of the drug's value has proved a different matter. Glaxo Wellcome says the drug reduces the duration of flu, the severity of the symptoms and the risk of secondary infections. But NICE says that, if used within 48 hours of the onset of symptoms, Relenza only reduces the duration of the illness by 24 hours — not the two to three days claimed by the company.

Crucially, because of the design of the clinical trials used by the company, NICE concluded there was “insufficient information to judge the extent to which the frequency of serious secondary complications in high-risk groups … might be reduced”. These groups are currently targeted by National Health Service (NHS) vaccination programmes. And, NICE says, it is difficult to see how most flu patients could be diagnosed within 48 hours within the NHS. Although some clinical work has shown that Relenza can limit the spread of flu between individuals in closed settings, it is not currently licensed for prevention.

The drug may have been the victim of unfortunate timing. With NICE needing to gain the confidence of the health professions, the public and parliament as early as possible, it would have been difficult for the government to reject its first advice.

NICE's rapid review of Relenza will not prejudice the full appraisal procedure that Relenza and a similar drug produced by the company Hoffman-La Roche are to undergo next year.