The Pharmaceutical Journal
Vol 273 No 7315 p304
4 September 2004

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Resistance to influenza drug higher than expected

Resistance to the antiviral drug oseltamivir may be higher than expected, new research shows.

Japanese researchers have investigated resistance to oseltamivir, a neuraminidase inhibitor, in a group of children with influenza. In 50 children being treated with the drug, nine (18 per cent) were found to have neura-
minidase mutations in positions known to confer resistance. Resistance was first detected four days after the start of treatment.

This level of resistance is higher than in previous reports. Kiso and colleagues, from the University of Tokyo, say that one explanation may be their rigorous detection techniques. They also note that lower paediatric oseltamivir doses may be used in Japan than in Europe or the US, which could be a contributory factor (Lancet 2004;364:759).

The researchers do not know whether the resistant viruses are less virulent or transmissible than normal.

Children, being more susceptible to influenza than adults, are seen as a useful group to study because they could provide a model similar to that of a general population during an influenza pandemic.

In an accompanying leading article (p733), Anne Moscona, from the Mount Sinai School of Medicine, New York, describes the Japanese data as a timely wake up call. “The study challenges our complacence about neuraminidase-inhibitor resistance,” she says.

Since stockpiles of antiviral drugs are a key part of contingency planning for an influenza pandemic, Dr Moscona says that it is vital to learn more about the incidence and mechanisms of resistance.

Cost concern Public health specialists are concerned about the cost of complying with National Institute for Clinical Excellence guidelines on use of oseltamivir to prevent influenza in nursing homes. NICE recommends that oseltamivir is given to all residents in nursing and residential homes each time a case of influenza-like illness is recognised in a resident or staff member and when flu is known to be circulating in the community.

The specialists, from the Royal Free hospital and the Health Protection Agency, have assessed the implications of this advice. From a survey last winter, they calculate that two-fifths of nursing homes have a case of influenza-like illness every week in winter. “The use of a single case of influenza-like illness as the threshold for prophylaxis may be impractical and costly,” they say, adding that further studies are needed to determine the best strategy for chemoprophylaxis. The study is published on BMJ Online this week.