Development and characterization of a liposome preparation by a pH-gradient method.
A pH gradient across liposome bilayers was established in order to load a model drug (orciprenaline sulphate) into liposome vesicles. This method of liposome loading resulted in yields as high as 80-85% encapsulation. An eight-step process was designed to scale-up the process and was evaluated. In this process a diafiltration technique was successfully used to remove the excess orciprenaline sulphate present in the external medium. Finally, drug-loaded liposomes were lyophilized using lactose as an internal and external liposomal cryoprotectant. Five-month stability data for the liposomes is reported. An HPLC technique was used to determine the drug concentration and a laser light-scattering technique was employed to determine the liposome vesicle size and polydispersity factor. Liposomes prepared by the pH-gradient method showed high encapsulation efficiency. Upon storage at 2-8 degrees C the vesicle size increased and encapsulation efficiency decreased with time. These phenomena are attributed to gradual fusion of liposomes and loss of drug to the extra-liposomal media.
Vemuri
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Department of Pharmaceutics, College of Pharmacy, University of Rhode Island, Kingston 02881-0809.
Rhodes
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D002214:Capsules; D004337:Drug Carriers; D005612:Freeze Drying; D006863:Hydrogen-Ion Concentration; D008081:Liposomes; D009921:Metaproterenol / Q000008:administration & dosage; D010316:Particle Size; D012995:Solubility; D013678:Technology, Pharmaceutical / Q000379:methods*; D014462:Ultrafiltration; D014867:Water
D002214:Capsules; D004337:Drug Carriers; D008081:Liposomes; D014867:Water; D009921:Metaproterenol