Infuenza Specialist Group

Until relatively recently, the only drugs available that had a true antiviral effect against influenza were the adamantanes, amantadine and rimantadine; however, rimantadine was not registered in many countries including Australia. The adamantanes are only active against influenza A virus, have a rather high rate of undesirable side effects and, when they are used to treat influenza result in the patient shedding drug-resistant viruses that retained their full ability to infect and cause illness in exposed people.

Although these drugs were used until quite recently, in particular for prophylaxis (prevention of infection) where the risk of inducing drug resistance was less, it has been found that many of the influenza A viruses in the human population have acquired adamantine resistance and the US Centres for Disease Control (CDC) have recommended against their use.

Based on research by Australian scientists in which the detailed structure of influenza virus neuraminidase was determined, it has been possible to develop a new family of drugs, the neuraminidase inhibitors, which interfere with the release of virus from the cells in which it has replicated. Two of these, zanamivir and oseltamivir, have now been widely registered as prescription medications for treatment and short-term prophylaxis (prevention) of influenza.

The two drugs have good safety profiles, are well tolerated and have similar effectiveness in the treatment and prevention of influenza. When used for treatment they must be administered within 48 hours of symptom onset in order to be effective and the earlier they are administered the more effective they are. Both drugs are reported to shorten the period of illness and the chance of complications.

Zanamivir is administered by inhaler whereas oseltamivir is taken orally. Many governments including the Australian Government have purchased stockpiles of the neuraminidase inhibitors for use in the event of an influenza pandemic.

Content Updated ( Monday, 26 November 2007 )