H2 Blockers

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H2 Blockers - Interactions and Warnings

The antacid was found to precipitate folic acid at a pH of greater than 4.0, thus removing it from the aqueous phase. This appears to be the explanation for the lowered folate absorption in the presence of antacid. Although the effects of these drugs on reducing folic acid absorption were relatively small, such reductions could become clinically significant in chronic antacid or H2 receptor antagonist use or intensive antacid or H2 receptor antagonist use by individuals eating diets that are marginal in folate content.
- J Lab Clin Med 1988 Oct;112(4):458-63 -- Effect of antacid and H2 receptor antagonists on the intestinal absorption of folic acid. -- Russell RM, Golner BB, Krasinski SD, Sadowski JA, Suter PM, Braun CL.

Cimetidine is known to interfere with other drugs through hepatic metabolism, the concentration of co-committant drugs such as warfarin, benzodiazepine tend to be elevated. Cimetidine should be replaced by the other H2RAs which have no such effects.
- Nippon Rinsho 2002 Aug;60(8):1613-7 -- What is important in treating elderly with H2 receptor antagonists -- Kurosawa S.

Cimetidine administration did not lead to malabsorption of unbound cobalamin but caused malabsorption of protein-bound cobalamin. Patients on cimetidine therapy malabsorb protein-bound cobalamin and, during long-term treatment, are at risk for developing cobalamin deficiency.
- Dig Dis Sci 1980 Mar;25(3):188-91 -- Malabsorption of protein-bound cobalamin but not unbound cobalamin during cimetidine administration. -- Steinberg WM, King CE, Toskes PP.

The use of H(2)-receptor antagonists and/or PPIs may impair the absorption of protein-bound dietary vitamin B(12) and could contribute to the development of vitamin B(12) deficiency with prolonged use. Patients taking these medications for extended periods of time, particularly >4 years, should be monitored for vitamin B(12) status.
- Ann Pharmacother 2002 May;36(5):812-6 -- Vitamin B(12) deficiency associated with histamine(2)-receptor antagonists and a proton-pump inhibitor. -- Ruscin JM, Page RL, Valuck RJ.

Gastric acid secretion has been demonstrated to facilitate iron absorption. Zinc absorption was reduced after cimetidine administration. Suggests that gastric acid secretion plays a role in the regulation of zinc absorption.
- J Am Coll Nutr 1991 Aug;10(4):372-5 -- Inhibition of gastric acid secretion reduces zinc absorption in man. -- Sturniolo GC, Montino MC, Rossetto L, Martin A, D'Inca R, D'Odorico A, Naccarato R.

Vitamin D absorption may be affected.
- J Lab Clin Med 1984 Oct;104(4):546-52 -- Hepatic vitamin D 25-hydroxylase inhibition by cimetidine and isoniazid. -- Bengoa JM, Bolt MJ, Rosenberg IH.

last update: November 2008

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