['Insufficient acid suppression is one of the main causes of proton pump inhibitor-refractory gastro-oesophageal reflux disease.', 'To achieve more potent and long-lasting acid suppression, different dosage regimens of rabeprazole were compared in relation to the CYP2C19 genotype status.', 'In a cross-over study, 18 healthy Helicobacter pylori-negative males (six homozygous extensive metabolizers, six heterozygous extensive metabolizers and six poor metabolizers) were given rabeprazole 10 mg once daily, 20 mg once daily or 10 mg twice daily, or water only (baseline data), for 7 days each. On day 7 of each regimen, 24-h intragastric pH-metry was performed.', 'No significant differences were observed in median pH values and pH>4 holding time ratios between rabeprazole 10 mg once daily and 20 mg once daily. However, with rabeprazole 10 mg twice daily, these parameters were significantly higher than those with 20 mg once daily. The potency of acid suppression by rabeprazole was influenced by the CYP2C19 genotype status. The differences were somewhat significant but not large. The incidence of nocturnal acid breakthrough was lowest with rabeprazole 10 mg twice daily.'] Is rabeprazole 10 mg twice daily superior to 20 mg once daily for night-time gastric acid suppression?