Effect of a rabeprazole half-dose twice daily on acid inhibition in patients with different CYP2C19 alleles.

Abstract

Fractional doses of proton pump inhibitors (PPIs) more often than once daily (qd) inhibit 24-h acid secretion more effectively than an increase in the standard single daily dose. Although rabeprazole 5 mg qd is covered for prevention of aspirin-induced gastric injury under the Japanese insurance system, it is unclear whether rabeprazole 5 mg twice daily (bid) would more effectively inhibit acid secretion. We compared acid inhibition between rabeprazole 10 mg qd and 5 mg bid in healthy volunteers with different alleles of CYP2C19. Twelve Helicobacter pylori-negative healthy volunteers (CYP2C19 genotypes: extensive metabolizer (EM) (n = 6) and poor metabolizer (PM) (n = 6)) received three kinds of regimen for 7 days under a randomized crossover design: rabeprazole 5 mg qd (5 mg QD), 10 mg qd (10 mg QD), and 5 mg bid (5 mg BID). A 24-hour pH monitoring was conducted before the trial and on day 7 of each regimen. No significant differences in median pH values (4.0 (1.9-5.9)) and (4.4 (2.1-6.5)) or percent time of pH ≥ 4 (50.7% (11.9-86.8%) and 56.8% (19.3-83.9%)) were seen between the 10 mg QD and 5 mg BID regimens. Median pHs and percent time of pH ≥ 4 in CYP2C19 PMs were significantly higher than those in EMs. With 5 mg BID, there was no significant difference in percent-time with pH ≥ 4 between daytime and nighttime, but the 10 mg QD showed a significant difference. Rabeprazole 5 mg bid provided no therapeutic advantage for acid inhibition compared with rabeprazole 10 mg qd, regardless of CYP2C19 genotype status.