SPRAY-DRYING OF LIPOSOMES FOR A PULMONARY ADMINISTRATION .2. RETENTION OF ENCAPSULATED MATERIALS

Extruded multilamellar vesicles containing atropine sulphate were spra y-dried in the presence of 10 % lactose. The particle mean diameter of the spray-dried product was about 7 mum and 3.5 mum when the spray-dr ier was equipped with a rotary atomizer or a nozzle, respectively. The size of the vesicles was not significantly modified after rehydration of the dry residue. Atropine sulphate was entrapped in liposomes cons tituted of soybean phosphatidylcholine (SPC), hydrogenated SPC and SPC :Cholesterol (1:1 molar ratio) with an efficiency of 4-6 %, but an imp ortant leakage (65 to 80 %) of the incorporated drug occurred during t he spray-drying process. On the other hand, alpha-tocopherol used as a lipophilic drug model was incorporated in SPC vesicles with an effici ency of 92 % and no significant leakage was detected during the dehydr ation-rehydration cycle. Thus, spray-drying constitutes an interesting method to dehydrate liposomes (especially when lipophilic drugs are i ncorporated) into the form of small particles that could be delivered to the respiratory tract and reconstituted in situ.