Stability of desmopressin loaded in liposomes

Desmopressin-containing liposome formulations have been developed for intranasal administration previously. Positively charged liposomes were found to be an efficient delivery system for desmopressin. In this study, stability of the loaded desmopressin in positively charged liposomes was further investigated. Comparison of the stability of desmopressin in solution and liposomes was made. Degradation of desmopressin was shown to follow a pseudo-first-order reaction. Degradation of desmopressin in both solution and liposomes demonstrated the same kinetic behavior and exhibited no significant difference in half-lives. Similar v-shape pH-rate profile was found for desmopressin degradation in solution and liposomes. At pH 4.0, the inflection point of the v-shape pH-rate curve, the reaction rate of desmopressin was lowest and the stability was greatest. The stability of lipid ingredients of dioleoylphosphatidylcholine (DOPC), cholesterol (C), and stearylamine (S) in the liposome dispersion at pH 4.0 was studied. Results demonstrated that DOPC, C, and S were relatively stable in the liposome structure when formulated with desmopressin. The degradation of desmopressin in solution and liposomes in the presence of alpha-chymotrypsin was investigated. A longer half-life for desmopressin in liposomes than in solution was observed. It was suggested that desmopressin was protected by the liposomes against alpha-chymotrypsin digestion.