Omeprazole and lansoprazole are not inducers of cytochrome P4501A2 under conventional therapeutic conditions

Objectives: Claims that substituted benzimidazole molecules induce cytochromes P4501A2 are still controversial. This study was undertaken to evaluate their inducing potency under conventional therapeutic conditions. Methods: Twelve healthy non-smoking young volunteers were given 20 mg omeprazole or 30 mg lansoprazole daily, in random order, for 2 weeks, separated by a 3 week wash-out period. We evaluated the CYP1A2 activity by the ratio of the molar urinary concentrations (GUM ratio) of the three end products of the paraxanthine demethylation of caffeine over the molar concentration of a paraxanthine 8-hydroxylation product. Results: This urinary metabolite ratio has previously been shown to be correlated with caffeine clearance. There was slight but non-significant enhancement of the CUM ratio after 2 weeks of treatment with omeprazole (3.62 (1.58) on Day 15 vs 3.09 (1.43) on Day 1), and after lansoprazole (4.26 (2.3) vs 3.65 (2.36)). Similarly, one week of treatment did not significantly alter the CUM ratio after omeprazole or lansoprazole (3.11 (1.58) and 3.28 (1.59), respectively on Day 8). Conclusion: The results show that both omeprazole and lansoprazole in the daily recommended therapeutic doses of 20 mg and 30 mg, respectively, have no influence on the metabolism of caffeine, and therefore no influence on cytochrome CYP1A2 activity.