Acido-Basic Properties of Proton Pump Inhibitors in Aqueous Solutions

Abstract

The pharmacological characteristics of proton pump inhibitors are related to their protolytic behavior estimated by their pK_a values. Lansoprazole is a potent anti-acid drug from this group. Because of its poor stability a rapid spectrophotometric method was developed for the determination of its pK_a values. Three pK_a values were obtained: an acidic pK_a1 = 8.84 and two basic, pK_a2 = 4.15 and pK_a3 = 1.33. These pK_a values were discussed from the point of lansoprazole structure and instability with the aim of locating basic and acidic moieties in the molecule of proton pump inhibitors. They were also compared with experimentally determined pK_a values from the literature and with some pK_a values calculated by different programs.

Keywords:

• proton pump inhibitors
• lansoprazole
• ionization constants
• spectrophotometric method
• pK_a values