A comparison of the acid-inhibitory effects of esomeprazole and rabeprazole in relation to pharmacokinetics and CYP2C19 polymorphism

Background Esomeprazole and rabeprazole are metabolised in the liver by means of the CYP2C19 enzyme, which has several functional genetic polymorphisms. Among Caucasians, 70% of the population has a fast metaboliser phenotype, 25-30% an intermediate and 2-5% a slow metaboliser phenotype. It is unknown whether different PPIs are affected to the same extent by these phenotypic differences. Aim To compare the acid-inhibitory effects of esomeprazole 40 mg and rabeprazole 20 mg in relation to CYP2C19 genotype and pharmacokinetics. Methods Eighteen healthy Helicobacter pylori-negative Caucasian subjects with CYP2C19*2-*6 and*17 genotype were included in a randomised investigator-blinded crossover study with esomeprazole 40 mg and rabeprazole 20 mg. Intragastric 24-h pH-monitoring was performed on days 0, 1 and 5 of oral dosing. Results Onset of acid inhibition during the first 4 h after administration did not differ significantly between PPIs. During the upright period, the proportion of time with pH >4 was significantly higher with esomeprazole compared to rabeprazole (52.2 vs. 40.3%, P = 0.003). At day 1 and 5, acid inhibition was significantly greater with esomeprazole than with rabeprazole (median intragastric pH: day 1: 3.7 vs. 3.0, P = 0.008; day 5: 4.7 vs. 3.8, P 4: day 1: 45 vs. 39%, P = 0.054; day 5: 65 vs. 48%, P