April 1991

Histamine2-Receptor Antagonists and Cardiovascular Drugs

Author Affiliations

Petah Tiqva, Israel

Arch Intern Med. 1991;151(4):814-815. doi:10.1001/archinte.1991.00400040142036

To the Editor.—  In the April 1990 issue of the Archives, Lipsy et al1 reviewed the various histamine2 receptor antagonists. I would like to comment on the section describing the drug interactions of histamine2 antagonists and cardiovascular drugs.The authors state that the clearance of propranolol is decreased by both cimetidine and ranitidine, thus causing increased levels of propranolol in the blood. However, whereas cimetidine increases propranolol concentrations in the blood and potentiates β-blocking effects through inhibition of hepatic microsomal enzymes and reduction of hepatic blood flow,2 ranitidine has no effect on propranolol metabolism or clearance.2The authors failed to address the interaction between histamine2 receptor antagonists and the calcium-channel blockers that are becoming increasingly popular. Increased blood levels of diltiazem are detected when this drug is administered concurrently with ranitidine and, more so, with cimetidine.3 Cimetidine causes increased levels of nifedipine, which might

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