Chemical stability and mechanism of degradation of omeprazole in solution

Abstract

The chemical stability and kinetics of omeprazole in buffer solutions at various pH values, 5.0, 8.0, and 10.0 were studied at three different stress conditions, 25, 40, and 50 C. It was found that the degradtion reaction followed the pseudo first-order kinetics and was quite rapid at low pH values with a half-life of 43 min at pH 5.0 and 25 C. In alkaline pH of 10.0 the drug was however remarkbly stable with a half-life of 2.8 months at 25 C. The energy of activation was pH-dependent and varied from 9.9-19.6 kcal/mol. The pH-log rate profiles in association with other thermodynamic activation parameters suggested that the main pathway of degradation reaction would be the hydrolysis with depending on hydronium ion concentration involving bimolecular reaction.