Development and characterisation of freeze-dried liposomes containing two anti-asthma drugs

Stable liposomes that offer a potential for pulmonary delivery have been developed and characterised. Freeze-dried soya phosphatidylcholine: cholesterol (1:1) small unilamellar liposome vesicles were prepared with salbutamol sulphate (SS) and beclometasone dipropionate (BDP), being included within separate or same formulations, and in presence or absence of a cryoprotectant. The cryoprotectants used were sucrose and trehalose in 5:1 or 10:1 (w/w) cryoprotectant to lipid ratio. Size analysis was performed using photon correlation spectroscopy and surface charge (zeta potential) was measured using laser Doppler velocimetry. Inclusion of a cryoprotectant prior to freeze-drying minimised the increase in the measured size on rehydration, with sucrose being superior to trehalose. When both SS and BDP were included, the rehydrated liposomes had the smallest size, being below 100 nm using sucrose and below 136 nm using trehalose. The zeta potential of the liposomes was slightly increased after freeze-drying and was highly independent on formulation. This study has demonstrated the possibility of producing stable freeze-dried liposomes that included two anti-asthma drugs and also demonstrated a potential for application in pulmonary delivery.