Comparison of five antisecretory agents acting via gastric H⁺/K⁺- ATPase

Lansoprazole(L), pantoprazole (P), rabeprazole® and RO-18-5364 (RO) are new benzimidazole derivatives which rival omeprazole (O) as proton pump inhibitors (PPIs) for treatment of ulcer disease. In this study, we compared the effects of these compounds on acid secretion and determined their relative potencies in relation to their effect on [¹⁴C]-aminopyrine (AP) accumulation in isolated gastric glands. Inhibition of AP (1.2 μCi-mL^-1) accumulation was measured in rabbit isolated gastric glands. dbcAMP (1 mmol; stimulant of acid secretion) and Ro 20-1724 (0.1 mmol; a phosphodiasterase inhibitor) were added to the Eppendorf tubes containing the PPIs and AP and dose-response curves were done for each drug after incubating for 5, 10 and 20 min at 37 °C and AP accumulation was determined using a scintillation counter. All the PPIs significantly (P<0.001) inhibited acid secretion as demonstrated by the inhibition of AP accumulation in the isolated gastric glands. Minimum inhibition occurred at a concentration of 0.001 μmol for lansoprazole and omeprazole, 0.01 μmol for rabeprazole and RO 18-5364 and 0.02 μmol for pantoprazole. No differences were observed between PPIs with regards to the maximum inhibition they produce. When expressed as a percentage inhibition of control at 10-min incubation and at concentrations of 1 μmol, L showed 85.6 ± 0.5, O 87 ± 0.5, P 83.2 ± 1.1, R 86.4 ± 1.1 and RO 87.8 ± 1.9 inhibition respectively. When comparing the IC₅₀ values, their relative potencies were different. Maximum potency was shown by L (0.007 μmol) > O (0.012 μmol) > R (0.018 μmol) > RO (0.034 μmol) > P (0.050 μmol). All the new PPIs showed different potencies as inhibitors of acid secretion as evident from their IC₅₀s. Extensive ulcer healing trials demonstrated comparable efficacy with a number of studies indicating that symptoms relief are more rapid with P and L, while in this study L appeared to be the most potent in inhibiting AP accumulation in the isolated gastric glands. (C) 2000 Elsevier Science Ltd.