Ranitidine is a histamine H2-receptor antagonist that inhibits stomach acid production. It is commonly used in treatment of peptic ulcer disease (PUD) and gastroesophageal reflux disease (GERD). Ranitidine is also used alongside fexofenadine and other antihistamines for the treatment of skin conditions such as hives. Ranitidine is also known to give false positives for methamphetamine on drug tests. A Ranitidine appears to decrease mucosal perfusion in patients with acute renal or cardiac failure, and increases their risk of death. All drugs in its class decrease gastric intrinsic factor secretion, which can significantly reduce absorption of protein-bound vitamin B12 in humans. Elderly patients taking H2 receptor antagonists are more likely to require B12 supplementation than those not taking such drugs. H2 blockers may also reduce the absorption of drugs (azole antifungals, calcium carbonate) that require an acidic stomach.
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