Zanamivir hydrate is the hydrated form of zanamivir, a potent and selective inhibitor of influenza virus neuraminidase. Its chemical structure is based on a 2,3-didehydro-2,4-dideoxy-4-guanidino-N-acetylneuraminic acid (DANA) scaffold, which mimics the natural substrate of the viral enzyme, sialic acid. As an active pharmaceutical ingredient (API), zanamivir is a key antiviral drug used for the treatment and prophylaxis of influenza A and B virus infections. It functions by competitively binding to the active site of viral neuraminidase, preventing the release of newly formed virions from infected host cells, thereby halting the spread of infection within the respiratory tract. It is administered via oral inhalation (e.g., Relenza). Zanamivir hydrate represents a significant class of neuraminidase inhibitors and is structurally categorized as a sialic acid analogue. Its development marked a major advance in anti-influenza therapy, offering a targeted mechanism of action against both seasonal and pandemic influenza strains.