Zanamivir flu drug, molecular model. Zanamivir is marketed under the trade name Relenza. It is administered in spray form for inhalation. This reduces the length of an attack of influenza (flu) if taken early in the course of the disease. It is a neuraminidase inhibitor, a drug that works by blocking the enzyme neuraminidase, which is found on the surface of the influenza virus. The enzyme aids the release of more virus particles from infected cells, and blocking its effect thus reduces the severity and duration of the symptoms. Relenza was the first such drug on the market, but it has since been made all but obsolete by the appearance of the related drug oseltamivir (Tamiflu), which can be taken in pill form. In this molecule, carbon atoms are yellow, oxygen is red, nitrogen is blue and hydrogen is white.