Aims: To investigate, by means of meal-stimulated acid secretion, the extent to which differences in plasma half-life, bioavailability and the recommended therapeutic dose can influence the antisecretory potency of lansoprazole and omeprazole, Methods: In this double-blind, placebo-controlled, crossover study, 10 healthy male volunteers received 15 mg or 30 mg lansoprazole, 20 mg or 40 mg omeprazole or placebo for 5 days, in a randomized order. Meal-stimulated acid secretion was determined by means of a homogenized test meal and intragastric titration. Results: On day 1, meal-stimulated acid secretion was decreased by 35% and 45% after administration of 15 mg or 30 mg lansoprazole, and by 16% and 42% after 20 mg or 40 mg omeprazole. After 3 and 5 days of dosing the decreases were 53% and 48% with 15 mg lansoprazole, 82% and 82% with 30 mg lansoprazole, 43% and 39% with 20 mg omeprazole, and 76% and 83% with 40 mg omeprazole. At all measuring points during the 5-day dosing periods, lansoprazole 15 mg and 30 mg proved superior to 20 mg omeprazole in inhibiting meal-stimulated gastric acid secretion, but the differences were only statistically significant for the lansoprazole 30 mg dose. 30 mg lansoprazole and 40 mg omeprazole proved equipotent, On day 1 only 30 mg lansoprazole was significantly better than placebo. Conclusion: This study demonstrated the following order of antisecretory potency: 30 mg lansoprazole = 40 mg omeprazole > 15 mg lansoprazole approximate to 20 mg omeprazole.
