Formulation and evaluation of novel reverse microemulsions containing salmon calcitonin in hydrofluoroalkane propellants.

To develop reverse microemulsion as a potential strategy for pulmonary delivery of salmon calcitonin (sCT) in HFA134a propellant of pressurized metered dose inhalers (pMDIs), pluronic P85 (P85) was chosen as the most appropriate surfactant to form microemulsions containing sCT. Formulation parameters, including the surfactant and ethanol content, water content, and sCT loading, were optimized to obtain two desired pMDI formulations A and B with clear and transparent appearance, Tyndall effect, good physical stability and aerosolization properties. Aerosolization properties of the optimized pMDIs were assessed by next generation impactor (NGI) and twin-stage impactor (TSI), and the dose of sCT in each stage was assayed by HPLC. The fine particle fraction (FPF) of formulations A and B were both at the range of approximately 28.0-36.0%. Cytotoxicity studies indicated the cell viability determined by MTT assay only slightly dropped when the A549 cells were exposed to the pMDI formulations. Pharmacological study performed on the male Wistar rats showed the intratracheal administration of the microemulsion pMDIs containing sCT exhibited similar but prolonged hypocalcemic activity compared with the intravenous injection of sCT solution. Therefore, such reverse microemulsions are potential for pulmonary delivery of therapeutic peptides using HFA-pMDIs.