4 October 2006

The antiviral drugs oseltamivir (Tamiflu) and zanamivir (Relenza) have only a limited role in seasonal influenza and vaccination remains the primary strategy for preventing influenza and its complications, according to the National Prescribing Service Limited (NPS).

An NPS position statement, the Role of the neuraminidase inhibitors oseltamivir (Tamiflu) and zanamivir (Relenza) in seasonal influenza, was released today.

NPS CEO, Dr Lynn Weekes, said the statement was prepared in response to an identified need, particularly in general practice. It was written primarily for GPs and pharmacists.

“We’ve heard a lot about these drugs and their potential role in an avian influenza pandemic, and their role in seasonal influenza was questioned. No vaccines are available for avian influenza, so antivirals might have a role in that context.

“There are vaccines for seasonal influenza and they have proven effectiveness for reducing influenza infection and its complications. On the other hand, the neuraminidase inhibitors have only a modest effect in treating seasonal influenza, reducing illness by about 1-1.5 days in otherwise healthy people.

“Judicious use of these drugs is important to reduce the risk of resistance and to preserve their possible usefulness,” Dr Weekes said.

NPS recommends neuraminidase inhibitors are not used to treat seasonal influenza in otherwise healthy people, however they do have a role in controlling institutional outbreaks of influenza, for example in residential aged care facilities.

The statement outlines why the effectiveness of these drugs is likely to be lower in clinical practice than in clinical trials. Key factors are that:

• the drugs must be started as soon as possible within 48 hours of contact with an influenza case or symptom onset — yet many patients will present after the treatment window of 48 hours.

• in trials, the benefits of neuraminidase inhibitors were clearer in laboratory-confirmed cases than in influenza-like illness — however influenza virus infection cannot be accurately diagnosed on clinical grounds alone.

The statement describes how each drug works, their adverse effects, the risk of resistance and the place in therapy and recommendations for treatment of seasonal influenza.

It is based on a thorough review of the evidence and has been reviewed by an expert panel and can be read at www.nps.org.au.

National Prescribing Service Limited (NPS) is an independent, non-profit organisation for Quality Use of Medicines. We provide accurate, balanced, evidence-based information and services to help people choose if, when and how to use medicines to improve their health and wellbeing. We are member-based and work in partnership with health professionals, government, pharmaceutical industry and consumers. NPS is funded by the Australian Government Department of Health and Ageing.