CHEMISORBATES OF P-HYDROXYBENZOIC ACID METHYL-ESTER ON SILICA AS A NEW-TYPE OF PRO-DRUG .4. DRUG-RELEASE FROM CHEMISORBATES DISPERSED IN LIPOPHILIC VEHICLES

The hydrolysis of the chemisorbate of p-hydroxybenzoic acid methyl est er (PHBAME) on porous silica (KG 100) incorporated in lipophilic vehic les such as liquid paraffin, synthetic oil Miglyol(R) 818 and white pe trolatum was examined in dissolution media at pH 2 and 7.4, respective ly. Chemisorbed PHBAME on KG 100 is released more rapidly in alkaline than in acidic dissolution fluids. Dispersions of the PHBAME-KG 100 ch emisorbate in lipophilic vehicles modify the hydrolysis significantly. Drug release from chemisorbate dispersed in lipophilic vehicles may b e controlled by the polarity of the vehicles. However, the viscosity o f the vehicle, and not the polarity, exerts the strongest influence on the drug release.