Acid catalyzed reactions of three proton pump inhibitors (PPIs), namely omeprazole, lansoprazole and pantoprazole, have been investigated and monitored by direct current polarography at dropping mercury electrode (D.M.E) in phosphate buffer (0.1 M) of pH 3-7.5. This gives well defined current-time profiles of individual electroactive degradation products along with their starting materials. The investigation shows that the order of stability of three PPIs can be written as: pantoprazole > omeprazole > lansoprazole. The rate of degradation of PPIs decreases with decreasing the basicity of the corresponding benzimidazole nitrogen of PPIs, as predicted by the effect of individual substituents on each of the benzimidazole rings. At pH 7.5 all three PPIs are almost stable and the observed half wave potentials (E 1/2 ) are -1.07 V for omeprazole, -1.25 V for lansoprazole and -1.32 V for pantoprazole. On decreasing the pH from 7.5 to 3.0 the anodic shift in E 1/2 values were observed along with degradation of the PPIs and simultaneous appearance of degradation products. The present study may provide an insight for designing more potent new proton pump inhibitors.

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