Preparation And Evaluation Of Chloroquine Encapsulated In Liposomes

Chloroquine diphosphate (CQ) is an important antimalarial drug for the treatment of all kinds of plasmodium infections and is widely used clinicly. The higher effective concentration and the life-threatening toxicity caused by a fast parenteral administration of CQ aqueous solution, which limits its clinical application. To decrease the toxic side effect, the liposomal CQ was prepared. The subcutaneous injection of liposomal CQ act as a local depot with a slow release of the drug which would improve the treatment efficacy and decrease the toxic side effect.In the study, HPLC determination was developed for CQ in vitro and it was validated by characterization of linearity, precision as well as accuracy. PBS (pH 7.4) was used to elute liposomes and then methanol solution was applied to destroy the structure of liposomes. The CQ in methanol solution and free CQ was respectively determined by HPLC and the encapsulation efficiency (EE) was calculated.This study developed a pH gradient method for encapsulating CQ into liposomes. The effect of different formulation factors on the encapsulation efficiency (EE) and the size of CQ liposome was investigated. These factors included the internal phase of liposomes (the composition of internal phase, the buffer concentration and the value of pH), the external phase of liposomes (the kind of base used to adjust the pH of exteral phase) , the ratio of drug to soybean phosphatidylcholine (drug/SPC), the ratio of cholesterol to soybean phosphatidylcholine (Chol/SPC), the incubation temperature and time. By the orthogonal design, the EE (94%) was obtained when using CQ 10mg, SPC 500mg and Chol 100mg at 0.10 M citrate-sodium citrate buffer (pH 3.6). As 5mol% methoxy-poly(etheyene glycol) cholesteryl succinate (CHS-PEG₂₀₀₀) or distearoyl phosphatidylethanolamine-poly (ethylene glycol) (DSPE-PEG₂₀₀₀) was added to prepare the sterically stabilized liposomes, the size of particle was reduced and the EE was improved. Freeze-drying with 5% trehalose as cryoprotectant was carried out to achieve long-term stability.The drug release studies were performed in vitro simulating the desired application conditions, such as pH 7.4, pH 6.5 and pH 5.5. Besides these, the infulence of formulation on the release was examed. As the result, the release of CQ from the liposomes prepared via remote loading showed the significant pH-sensitivity and retention properties, which favored the application of liposomal CQ at endosomal compartments.Liposomal CQ and free CQ were administered via subcutaneous injection at the equal dose. This paper described a simple and rapid HPLC method with the piperaquine phosphate as internal standard for the determination of CQ in rat plasma and whole blood. The pharmacokinetics properties of liposomal CQ were compared to that of free CQ in rats and the AUC value of the liposomal CQ increased more than 4-fold versus that of free CQ.The whole blood pharmacokinetics studies of liposomal formulation tested showed that the elimination profile of encapsulated CQ was very similar to that of a sustained-release system with the increasing AUC, prolonging t1/2 beta and decreasing the total clearance.