Ranitidine at very large doses does not inhibit theophylline elimination

Area of Science:

• Pharmacology
• Drug Metabolism
• Clinical Pharmacology

Background:

• Ranitidine is widely believed not to alter drug metabolism, based on most controlled human studies.
• However, some evidence suggests ranitidine may possess drug metabolism inhibitory properties.
• Potential inhibition might be dose-dependent, becoming apparent at higher ranitidine dosages.

Purpose of the Study:

• To investigate the effects of high-dose ranitidine (1200 mg/day and 4200 mg/day) on theophylline elimination.
• To compare the effects of high-dose ranitidine with a known drug metabolism inhibitor, cimetidine (1200 mg/day).
• To determine if ranitidine inhibits drug metabolism, particularly theophylline, at supra-therapeutic doses.

Main Methods:

• A controlled study design was employed to assess drug interactions.
• Participants received either high-dose ranitidine (1200 mg/day or 4200 mg/day) or standard-dose cimetidine (1200 mg/day).
• Theophylline elimination and clearance were measured to evaluate drug metabolism changes.

Main Results:

• Cimetidine significantly decreased theophylline clearance in 11 out of 12 subjects by an average of 19.4%.
• Neither the 1200 mg/day nor the 4200 mg/day dose of ranitidine affected theophylline disposition or clearance.
• No detectable effect on theophylline elimination was observed even with ranitidine doses up to fourteenfold higher than typically prescribed.

Conclusions:

• Contrary to some case reports, this controlled study found no evidence that ranitidine inhibits theophylline metabolism.
• Even at significantly elevated doses, ranitidine did not alter theophylline elimination in human subjects.
• These findings support the general consensus that ranitidine does not significantly inhibit drug metabolism.