Characterization and stability of various liposome-encapsulated enoxacin formulations

The necessity for antibacterial agents with greater intracellular efficacy has led to the development of endocytosable drug carriers such as liposomes. Enoxacin was selected as a model drug incorporated in various liposome formulations as a therapeutic dosage form using the ethanol injection method and freeze-drying. Liposomal behavior after preparation and stability test was characterized by determining the physicochemical properties of enoxacin encapsulation percent, vesicle size and turbidity. The non-phospholipid formulation of stratum corneum liposomes showed the highest encapsulation efficiency after preparation among nine liposomal formulations. The addition of dissacharides in liposomes also enhanced the encapsulation of enoxacin due to the protection of phospholipid bilayers during the freeze-drying process. The liposomes with negatively charged component and dissacharides showed lower enoxacin leakage after five weeks of storage at 45 degrees C, suggesting these formulations have high stability in long-term storage. The negative liposomes showed a different behavior than others in their decrease of size and turbidity during storage, possibly due to high surface charges of the negative formulation. Cholesterol stabilized bilayers interacted with plasma and high density lipoprotein (HDL) retained enoxacin in the vesicles. Nevertheless, liposomes with cholesterol caused a hydrolysis problem after incubation with normal saline. The formulation with trehalose not only showed high stability in storage but also in plasma and HDL. This suggested trehalose was useful to incorporate with phospholipids to produce a highly encapsulated and stabilized liposomes of enoxacin. This study also demonstrated that thought is required in utilizing turbidity as a direct index of liposomal vesicle size.