Liposomal amikacin dry powder inhaler: Effect of fines on in vitro performance

The aim of the present investigation was to prepare and evaluate the influence of adding fines on the in vitro performance of liposomal amikacin dry powder inhaler (AMK LDPI) formulations. Liposomes composed of hydrogenated soyaphosphatidylcholine, cholesterol and saturated soyaphosphatidylglycerol (AMK 1), or stearylamine (AMK 2) were prepared by a reverse phase evaporation technique, extruded to reduce size and separated from unentrapped drug. Purified liposomal dispersion was subjected to lyophilization using optimized cryoprotectant to achieve maximum percentage drug retention (PDR). Lactose carrier in varying mass ratios with or without addition of fines in different mixing sequences was used to formulate AMK LDPI formulations. AMK LDPI formulations were characterized for angle of repose, compressibility index, dispersibility index, scanning electron microscopy, and fine particle fraction (FPF). PDR was found to be 97.6% +/- 2.2% for AMK1 and 98.5% +/- 1.9% for AMK2 using sucrose as optimized cryoprotectant in lipid: sucrose ratio of 1:4. Lactose carrier containing 10% fines (wt/wt) was found to be the optimum blend at 1:5 mass ratio of liposome:lactose. The addition of fines and the order of mixing of fines were found to influence the FPF with significantly different device fractions. FPF of AMK LDPI formulations using Rotahaler as the delivery device at 30, 60, and 90 L/min were found to be 21.85% +/- 2.2% and 24.6% +/- 2.4%, 25.9% +/- 1.8% and 29.2% +/- 2.1%, and 29.5% +/- 2.6% and 34.2% +/- 2.0% for AMK1 and AMK2, respectively. From the studies performed in this investigation, it was observed that liposomal charge, addition of fines and order of mixing fines, has a significant effect from LDPI formulation.