Effect of histamine H2-receptor antagonists on vitamin B12 absorption.
OBJECTIVE
To discuss the potential of histamine H2-receptor antagonists (H2RAs) to cause malabsorption of vitamin B12 (cyanocobalamin).


METHODS
Pertinent literature was identified via a MEDLINE search. Journals and references cited in published articles also were used as data sources.


METHODS
Studies evaluating the effect of H2RAs on vitamin B12 absorption were reviewed.


RESULTS
H2RAs decrease acid secretion by the gastric parietal cells. Gastric acid and pepsin produced by these cells are required for the cleavage of vitamin B12 from dietary sources. Intrinsic factor (IF), also produced by gastric parietal cells, is required for vitamin B12 absorption from the gastrointestinal tract. Although H2RAs have not conclusively been shown to decrease IF secretion, studies have demonstrated a significant reduction in food-bound vitamin B12 absorption secondary to decreased acid secretion in patients taking these drugs.


CONCLUSIONS
H2RAs have the potential to cause vitamin B12 deficiency. This may be important in patients with inadequate stores of vitamin B12 (e.g., poor diet), particularly those receiving H2RA therapy continuously for more than two years. Healthcare providers should be aware of this potential adverse effect.
Force
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RW
College of Pharmacy, Ohio State University, Columbus 43210.
Nahata
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MC
D002927:Cimetidine / Q000627:therapeutic use; D002986:Clinical Trials as Topic; D006635:Histamine H2 Antagonists / Q000494:pharmacology* / Q000627:therapeutic use; D006801:Humans; D007408:Intestinal Absorption / Q000187:drug effects*; D010437:Peptic Ulcer / Q000503:physiopathology / Q000628:therapy; D011899:Ranitidine / Q000627:therapeutic use; D014805:Vitamin B 12 / Q000378:metabolism*
D006635:Histamine H2 Antagonists; D002927:Cimetidine; D011899:Ranitidine; D014805:Vitamin B 12