The formulation-performance relationship of multiple emulsions and ocular activity

Abstract

Multiple emulsions containing prednisolone were prepared using a two step emulsification technique. The effect of various concentrations of hydrophilic and lipophilic emulsifiers (Tween-20 and Span-60) in multiple emulsions based on liquid paraffin on the drug bioavailability and duration of action as a controlled release formulation was studied following instillation in the rabbit's eye. The parameter of ocular activity such as area under the intraocular pressure/time curve (AUC); time for maximum response (TMR) and half value duration (HVD) were assessed for the o/w/o and w/o/w multiple emulsions. It was found that the hydrophilic emulsifier reduced the bioavailability but increased the concentration of lipophilic emulsifier to bring about the reverse effect. Therefore the bioavailability of the drug can be controlled by the proper choice and concentration of the emulsifier in the preparation of emulsions. The hydrophile-lipophile balance (HLB) values calculated for a surfactant mixture in a multiple emulsion was found to be highly negatively correlated to the values of the parameters of ocular activity. Decreasing the HLB value of the surfactant mixture in a w/o/w emulsion favours the bioavailability; the intensity and duration of drug action. © 1994.