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Comparison of the Effects of Over-the-counter Famotidine and Calcium Carbonate Antacid on Postprandial Gastric Acid A Randomized Controlled Trial

Mark Feldman, MD
JAMA. 1996;275(18):1428-1431. doi:10.1001/jama.1996.03530420056036.
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Objective.  —To compare an over-the-counter histamine2-receptor antagonist with an antacid as gastric acid reducers.

Design.  —Randomized, double-blind, placebo-controlled crossover trial.

Setting.  —Gastric secretory research laboratory in a Veterans Affairs medical center.

Participants.  —Eighteen healthy volunteers (10 men and 8 women) aged 25 to 62 years with normal gastric acid secretion rates.

Interventions.  —The subjects received the histamine2-receptor antagonist famotidine (Pepcid AC, 10 mg), calcium carbonate antacid tablets (Turns, 1000 mg), or placebo medications 1 hour after a test meal. Two identical meals were taken 2.5 and 6.0 hours after the medication was given.

Main Outcome Measures.  —Intragastric pH was maintained at 4.0 by in vivo intragastric titration with 0.3N sodium bicarbonate for 10 hours (1 hour before and 9 hours after medication). Reduction in sodium bicarbonate titrant use in the 2 treatment groups compared with titrant use with placebo was reflective of acid secretion inhibited by famotidine or acid neutralized by calcium carbonate tablets.

Results.  —When evaluated in increments of 30 minutes, calcium carbonate had a rapid onset of action, neutralizing 6.7 mmol of acid in the first 30 minutes. However, its duration of effect was only 60 minutes. Famotidine had a delayed onset of action compared with antacid, beginning after 90 minutes. However, famotidine had a duration of effect of at least 540 minutes. At its peak effect, 210 minutes after administration, famotidine reduced acid secretion by 7.3 mmol per 30 minutes.

Conclusions.  —Recommended over-the-counter doses of famotidine and calcium carbonate tablets have different pharmacokinetic profiles when taken in the postprandial period. The antacid has a rapid onset and short duration of action, while the histamine2-receptor antagonist has a delayed onset and a prolonged duration. Their peak potencies are similar.(JAMA. 1996;275:1428-1431)


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