Preparation, characterization and pulmonary pharmacokinetics of a new inhalable zanamivir dry powder.

This work describes a new dry powder for inhalation containing zanamivir, which is less hygroscopic than Relenza®. The powders were prepared via a spray-drying technique using mannitol as the carrier. A 5(3) central composite design was used to optimize the formulations. The final optimized powders, characterized with an angle of repose 37.48°, an aerodynamic diameter of 2.346 μm and in vitro deposition of 58.54%, were obtained by using the predicted variable values. Relenza® absorbed a significant amount of water at 66%, 75% and 85% relative humidity (RH; weight changes of approximately 1.38%, 2.18% and 3.72%, respectively). In contrast, the weight change for the zanamivir dry powder inhalation (DPI) was negligible when the RH was increased to 66%. The in vivo potential for the optimized powders was studied further in rats via the endotracheal administration of an 8.4 mg/kg dose. The bioavailability was 116% relative to Relenza®. Fluorescence imaging monitored the zanamivir dry powder inhalers in rats. The results indicated that the zanamivir DPIs were effectively delivered to the lung. These results indicate that the spray-dried zanamivir DPIs were promising for pulmonary delivery.