Oseltamivir is an inhibitor of influenza neuraminidase . Oseltamivir is a prodrug that is converted by intestinal and/or hepatic esterases to the neuraminidase inhibitor molecule, oseltamivir carboxylate. Neuraminidase cleaves the terminal a-Neu5Ac residues from the newly synthesized virion progeny and let it elute from the infected cell and seek new host cells to infect. Oseltamivir efficiently block sialidase activity and significantly inhibit the releasing mechanism . In the treatment of adults, oseltamivir reduces the time to first alleviation of symptoms and investigator mediated unverified pneumonia. In prophylaxis trials, oseltamivir reduced symptomatic influenza in participants by 55%. Oseltamivir also has some harm. Adults treated with oseltamivir are associated with an increased risk of nausea. And in prophylaxis trials there is an increased risk of headaches on-treatment . As a neuraminidase inhibitor, the substitution of the amino acid histidine to tyrosine at position 275 (H275Y) in the neuraminidase gene of H1N1 can cause the resistance of oseltamivir .