RESUMO
Objective: To develop a method for determining the entrapment efficiency of sinomenine hydrochloride (SM-HCl) liposomes and to illuminate the drug retention property in the liposomes. Methods: Thin film hydration method was employed to prepare SM-HCl liposomes. HPLC was used to determine drug content of the liposomes. A Kromasil ODS C18 column (250 mm x 4.6 mm, 5 μ) was used with an isocratic elution composed of methanol, water, and ethylenediamine in the ratio of 55 : 45 : 0.225 at a flow rate of 1.0 mL/min. The column was maintained at 30 °C. The UV detector was set at 265 nm. Centrifugation sedimentation combined with centrifugation ultrafiltration was used to determine drug entrapment efficiency of the liposomes. The entrapment efficiencies of an SM-HCl liposome sample (hydrated with citric buffer solution at pH 7.0) and its diluted sample were compared. Results: The pharmaceutical excipients and solvents for analysis had no interference with the determination of sinomenine. Sinomenine had a good linear relation in the range of 9.82-78.6 μg/mL (r = 0.999 7), the intra-day and inter-day precisions were with RSD≤2.1% and the averaged recovery was within 99.29%-100.8%. SM-HCl solution (50 μL) was able to saturate the drug absorption of ultrafiltration films. The entrapment efficiencies of the SM-HCl liposome sample (hydrated with citric buffer solution at pH 7.0) and its double-volume diluted sample were 33.16% and 14.75%, respectively. Conclusion: HPLC and centrifugation sedimentation combined with centrifugation ultrafiltration are able to determine the entrapment efficiency of SM-HCl liposomes efficiently and accurately. Initial filtrate (50 μL) should be discarded in the process of ultrafiltration in order that the drug concentration in filtrate may be equal to that of external aqueous phase of liposomes. The retention of sinominine in the liposomes is poor, although it has considerable affinity to the lipid bilayers.