Zanamivir is a medication used to treat and prevent influenza caused by influenza A and influenza B viruses. It is a neuraminidase inhibitor and was developed by the Australian biotech firm Biota Holdings. It was licensed to Glaxo in 1990 and approved in the US in 1999, only for use as a treatment for influenza. In 2006, it was approved for prevention of influenza A and B.  Zanamivir was the first neuraminidase inhibitor commercially developed. It is marketed by GlaxoSmithKline under the trade name Relenza as a powder for oral inhalation. Medical uses
Zanamivir is used for the treatment of infections caused by influenza A and influenza B viruses, but in otherwise-healthy individuals, benefits overall appear to be small. It decreases the risk of ones getting symptomatic, but not asymptomatic influenza. The combination of diagnostic uncertainty, the risk for virus strain resistance, possible side effects and financial cost outweigh the small benefits of zanamivir for the prophylaxis and treatment of healthy individuals.Since then, genes expressing resistance to zanamivir were found in Chinese people infected with avian influenza A H7N9 during treatment with zanamivir. Treatment
In otherwise-healthy individuals, benefits overall appear to be small. Zanamivir shortens the duration of symptoms of influenza-like illness (unconfirmed influenza or the flu) by less than a day. In children with asthma there was no clear effect on the time to first alleviation of symptoms. Whether it affects the risk of ones need to be hospitalized or the risk of death is not clear.
The discovery was initially funded by the Australian biotechnology company Biota and was part of Biotas ongoing program to develop antiviral agents through rational drug design. Its strategy relied on the availability of the structure of influenza neuraminidase by X-ray crystallography. It was also known, as far back as 1974, that 2-deoxy-2,3-didehydro-N-acetylneuraminic acid (DANA), a sialic acid analogue, is an inhibitor of neuraminidase.Computational chemistry techniques were used to probe the active site of the enzyme, in an attempt to design derivatives of DANA that would bind tightly to the amino acid residues of the catalytic site, so would be potent and specific inhibitors of the enzyme. The GRID software by Molecular Discovery was used to determine energetically favourable interactions between various functional groups and residues in the catalytic site canyon. This investigation showed a negatively charged zone occurs in the neuraminidase active site that aligns with the C4 hydroxyl group of DANA. This hydroxyl is, therefore, replaced with a positively charged amino group; the 4-amino DANA was shown to be 100 times better as an inhibitor than DANA, owing to the formation of a salt bridge with a conserved glutamic acid (119) in the active site. Glu 119 was also noticed to be at the bottom of a conserved pocket in the active site that is just big enough to accommodate the larger, but more basic guanidine functional group.