Effect of omeprazole 10 mg on intragastric pH in three different CYP2C19 genotypes, compared with omeprazole 20 mg and lafutidine 20 mg, a new H2‐receptor antagonist

Summary Background : Omeprazole 10 mg is used as maintenance therapy for gastro-oesophageal reflux disease, but previous reports have not mentioned the potency of its acid suppression. Aim : To evaluate the potency of acid suppression with omeprazole 10 mg, in relation to CYP2C19 genotypes. Methods : Eighteen healthy subjects without Helicobacter pylori participated. After a 7-day regimen of omeprazole 10 mg, 20 mg, lafutidine 20 mg (a novel H2-receptor antagonist) or water only (baseline data), intragastric pH was measured for 24 h. Results : With omeprazole 10 mg, greater differences were observed than 20 mg in median pH values and pH > 4 holding time ratios between poor metabolizers (PMs, n = 6) and the others [homozygous extensive metabolizers (homo-EMs, n = 6) and heterozygous extensive metabolizers (hetero-EMs, n = 6)]. With lafutidine 20 mg, these parameters were not influenced by the genotype. The potency of acid suppression was: omeprazole 20 mg ≈ lafutidine 20 mg > omeprazole 10 mg in homo-EMs, omeprazole 20 mg > omeprazole 10 mg ≈ lafutidine 20 mg in hetero-EMs, and omeprazole 20 mg ≈ omeprazole 10 mg > lafutidine 20 mg in PMs. Conclusions : Omeprazole 10 mg strongly suppresses acid secretion, but depending on the CYP2C19 genotypes shows greater interindividual variations in suppression than 20 mg.