gastrointestinal disorders
Medications for the Treatment of Gastric Acidity
H2 Blockers
These medications (cimetidine,famotidine, available IV and orally; andnizatidineavailable orally) are competitive inhibitors of histamine at the H2 receptor, thus suppressing gastrin-stimulated acid secretion and proportionately reducing gastric juice volume. Histamine-mediated pepsin secretion is also decreased.Nizatidine,famotidine, andcimetidineare available without a prescription in the United States. H2 blockers are well absorbed from the gastrointestinal tract, with onset of action 30 to 60 minutes after ingestion and peak effects at 1 to 2 hours. IV administration produces a more rapid onset of action. Duration of action is proportional to dose and ranges from 6 to 20 hours. Doses should often be reduced in older patients. For Peptic Ulcer Disease , once daily oral administration of The H2 blockerranitidine(oral, IV, and over the counter) has been removed from the market in the United States and in many other countries because of unacceptable concentrations ofN-nitrosodimethylamine (NDMA), a probable human carcinogen.Cimetidineandfamotidineare alternatives and do not contain NDMA, nor do proton pump inhibitors. Cimetidinehas minor antiandrogen effects expressed as reversible gynecomastia and, less commonly, erectile dysfunction with prolonged use. Mental status changes, diarrhea, rash, drug fever, myalgias, thrombocytopenia, and sinus bradycardia and hypotension after rapid IV administration have been reported with all H2 blockers, generally in<1% of treated patients but more commonly in older patients. Cimetidineand, to a lesser extent, other H2 blockers interact with the P-450 microsomal enzyme system and may delay metabolism of other medications eliminated through this system (eg,phenytoin,warfarin,theophylline,diazepam,lidocaine). 