Zanamivir: an influenza virus neuraminidase inhibitor.

Colman, P M

Zanamivir is the first of two registered neuraminidase inhibitors for the treatment and prophylaxis of influenza. Relenza, an orally inhaled powder form of zanamivir, is currently approved in 19 countries for treatment, and in two for prophylaxis. Relenza reduces the time to alleviation of symptoms by 1 to 2 days in the influenza-positive population, if taken within 48 h of symptom onset, and in prophylaxis in family settings, it confers an 80% reduction in the odds of contracting influenza. The resistance profile of zanamivir is encouraging in the sense that there are still no reports of patients on acute therapy shedding drug-resistant virus. However, patient uptake of the inhaled drug has been insufficient to conclude that drug resistance will not be an issue in the future. All zanamivir-resistant variants selected in the laboratory so far have diminished viability.