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.
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.


OBJECTIVE
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 approximately lafutidine 20 mg > omeprazole 10 mg in homo-EMs, omeprazole 20 mg > omeprazole 10 mg approximately lafutidine 20 mg in hetero-EMs, and omeprazole 20 mg approximately 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.
Shimatani
T
T
Department of General Medicine, Hiroshima University Hospital, Hiroshima, Japan. tshima@hiroshima-u.ac.jp
Inoue
M
M
Kuroiwa
T
T
Horikawa
Y
Y
Mieno
H
H
Nakamura
M
M
D000081:Acetamides / Q000008:administration & dosage* / Q000494:pharmacology; D000328:Adult; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics; D002940:Circadian Rhythm; D018592:Cross-Over Studies; D065731:Cytochrome P-450 CYP2C19; D005744:Gastric Acid / Q000502:physiology*; D005745:Gastric Acidity Determination; D005838:Genotype; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008297:Male; D008365:Manometry; D006899:Mixed Function Oxygenases / Q000235:genetics; D009853:Omeprazole / Q000494:pharmacology*; D010880:Piperidines / Q000008:administration & dosage* / Q000494:pharmacology; D011446:Prospective Studies; D011725:Pyridines / Q000008:administration & dosage* / Q000494:pharmacology; D011970:Receptors, Histamine H2 / Q000008:administration & dosage* / Q000502:physiology
D000081:Acetamides; D010880:Piperidines; D011725:Pyridines; D011970:Receptors, Histamine H2; C076948:lafutidine; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C045793:CYP2C19 protein, human; D065731:Cytochrome P-450 CYP2C19; D009853:Omeprazole