THE RELEASE OF DRUGS FROM MONOGLYCERIDE-WATER LIQUID-CRYSTALLINE PHASES

The in vitro release of model drugs, with a wide range of aqueous solubilities, from monoolein-water liquid crystalline matrix systems has been investigated. Release of melatonin, pindolol, propranolol and pyrimethamine from individual systems with initial drug loading concentrations within the range 1-20% w/w and atenolol from systems at concentrations up to 10% w/w could be fitted to both diffusion-controlled or first-order kinetics. The release of atenolol at initial drug loading concentrations of 15 and 20% w/w could be fitted to a zero-order release model. Release rates have been related to the solubility of the drugs in the monoolein-water systems. Changes in the matrix monoolein/water weight ratio over the range 4:1-1:1 had no significant influence on drug release. Monoolein-water-drug systems prepared using drugs with either a high solubility (propranolol) or a low solubility (pyrimethamine) were stable when stored in the dark at 4 degrees C for up to 6 months with no significant change in release characteristics. Systems incorporating propranolol were unstable when stored at 26 degrees C for 15 days; storage of systems incorporating pyrimethamine under the same conditions were stable with no change in release characteristics.