Pharmacy Clinic
Treatment of Heart Burn

II        H2 antagonists:

H2 antagonists inhibit competitively the interaction of histamine with H2 receptor, they are highly selective and have
little or no effect on H1-or other receptors.

H2 antagonists also inhibit acid secretion stimulated by gastrine and, to a lesser extent by muscarinic a gonists.

Adverse Reactions

All four H2-RAs are extremely well tolerated, they may be associated with a rare, idiosyncratic, adverse event such as
bone marrow suppression or interstitial nephritis. They may induce mental confusion, particularly in seriously ill
patients with multiple organ failures.

Because cimetidine, and to a lesser extent ranitidine, increases serum concentrations of prolactin, it has been
associated with the development of gynecomastia in men and galactorrhea in women. It also blocks the binding of
dihydrotestosterone to androgen receptors, thus contributing to impotence and loss of libido in men receiving high
doses.

A number of drug interactions with cimetidine have also been reported, usually the result of cimetidine's binding to
hepatic cytochrome P-450, thus impairing the hepatic metabolism of the other drug. The H2-RAs may compete for
renal tubular secretion (eg, elevating serum creatinine level by 15% and impairing secretion of procainamide and
theophylline). Moreover, as drugs that decrease intragastric acidity, they may affect the absorption of certain other
drugs, such as ketoconazole.