Neuraminidase inhibitors

These are probably the best-known antiviral drugs. Oseltamivir (Tamiflu®) and Zanamivir (Relenza®) are both neuraminidase inhibitors. Influenza viruses that infect humans, including H5N1 bird flu, are largely susceptible to these two drugs. However, the virus can develop resistance to them.

Tamiflu® is supplied in capsule form. Relenza® is a powder which must be inhaled using a device called a Diskhaler®.

A third neuraminidase inhibitor, peramavir, is also under development and being used in some specific situations. This drug is given intravenously.

When used to treat a flu case, the drugs must be given within 48 hours of the patient developing symptoms. Ideally, it should be given within eight hours. Studies show neuraminidase inhibitors shorten the length of seasonal flu infection by one day. Some studies suggest they may also reduce the risk of complications. Neither drug has been shown to prevent death when treating seasonal flu.

However, many experts feel that these drugs will have a big role in a flu pandemic. They believe early treatment with neuraminidase inhibitors is likely to significantly reduce the severity of the illness, the complication rate, and possibly the death rate.

Both oseltamivir and zanamivir are about 80 percent effective in prophylaxis against seasonal flu. Not all countries that have approved these medications for treating flu have approved them for prophylactic use. In addition, they are not necessarily approved for pediatric use.

In the USA, oseltamivir was approved for prophylaxis in children over 1 year of age in December 2005, and zanamivir was approved for prophylactic use in March 2006.