Relenza (Zanamivir for Inhalation) has been approved for the treatment of uncomplicated acute illness due to influenza virus in adults and adolescents 12 years and older who have been symptomatic for no more than two days. Patients inhale Relenza orally using a hand-held, breath activated device called a Diskhaler. A couple of puffs delivers Relenza to the surface of the lungs, the primary site of influenza infection, where the drug is thought to inhibit the virus from multiplying. Administered within the first two days of symptom onset, Relenza reduces the duration of flu-related symptoms. Patients orally inhale 10 mg of Relenza twice a day for five days.

The most common side effects occurred in 3% or less of patients and were at rates comparable to placebo. Side effects included sinusitis, diarrhea, and nausea.

Relenza belongs to a new class of compounds called neuraminidase inhibitors. Neuraminidase is an enzyme, which breaks the bond holding new virus particles to the infected cell. Once broken, the new viruses are free to infect other cells, spreading the infection. Relenza is thought to work by inhibiting breakage of the bond and preventing release of the new viruses, therefore interrupting the spread of infection within the respiratory tract.