Chemisorbates of p-hydroxybenzoic acid methyl ester on silica as a new type of pro-drug IV. Drug release from chemisorbates dispersed in lipophilic vehicles

The hydrolysis of the chemisorbate of p -hydroxybenzoic acid methyl ester (PHBAME) on porous silica (KG 100) incorporated in lipophilic vehicles such as liquid paraffin, synthetic oil Miglyol® 818 and white petrolatum was examined in dissolution media at pH 2 and 7.4, respectively. Chemisorbed PHBAME on KG 100 is released more rapidly in alkaline than in acidic dissolution fluids. Dispersions of the PHBAME-KG 100 chemisorbate in lipophilic vehicles modify the hydrolysis significantly. Drug release from chemisorbate dispersed in lipophilic vehicles may be controlled by the polarity of the vehicles. However, the viscosity of the vehicle, and not the polarity, exerts the strongest influence on the drug release.