Pall Thor Ingvarsson and Gudjon Bjarki Hildarson
Monocaprin has potential as an eye drop formulation due to its antimicrobial activity against the common culprits in conjunctivitis. It is however a poorly soluble and unstable molecule. Self-nanoemulsifying drug delivery systems (SNEDDS) can improve monocaprin solubility, creating lipid droplets dispersed in water. Removing the water may then increase the stability of monocaprin through reduced molecular motion. Spray-drying is a gentle drying method suitable for unstable drugs and we hypothesize that by combining SNEDDS formulations with spray drying we can develop stable formulations that can be stored and transported in dry state, followed by redissolution on-site.
Propylene glycol and methoxypolethylene glycol were used as lipophilic solvents, labrasol and tween 20 served as surfactants. For spray-drying development, outlet temperatures of 60-90 °C were evaluated and trehalose was added as a stabilizing excipient in concentration of 4:1-9:1 (trehalose:lipid phase, w:w). Yield was measured by weighing the collected material. Monocaprin stability during processing and storage at 25 °C and 40 °C for two weeks was estimated through pH measurements.
Both outlet temperature and trehalose content influenced the yield, decreasing with higher outlet temperatures (from 69% to 52%) and increasing with higher trehalose concentration (from 44% to 75%). Solution pH before and after spray-drying was 7.0. Upon storage as a solution the pH dropped to 4.7-5.1 whereas when stored as spray-dried powder, the resulting solution pH was 6.7-6.9
Spray-drying is a promising method for formulating dry powder monocaprin emulsions that can be stored and distributed in dry form and redissolved on-site.
