Spray-Drying of Liposomes for a Pulmonary Administration. II. Retention of Encapsulated Materials

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Abstract
Extruded multilamellar vesicles containing atropine sulphate were spray-dried in the presence of 10 % lactose. The particle mean diameter of the spray-dried product was about 7 μm and 3.5 μm when the spray-drier 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 constituted of soybean phosphatidylcholine (SPC), hydrogenated SPC and SPC: Cholesterol (1:1 molar ratio) with an efficiency of 4–6%, but an important leakage (65 to 80%) of the incorporated drug occurred during the spray-drying process. On the other hand, α-tocopherol used as a lipophilic drug model was incorporated in SPC vesicles with an efficiency of 92 % and no significant leakage was detected during the dehydration-rehydration cycle. Thus, spray-drying constitutes an interesting method to dehydrate liposomes (especially when lipophilic drugs are incorporated) into the form of small particles that could be delivered to the respiratory tract and reconstituted in situ.