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Aliment Pharmacol Ther. 2007 Jan 1;25(1):103-9.

Comparison of gastric pH with omeprazole magnesium 20.6 mg (Prilosec OTC) o.m. famotidine 10 mg (Pepcid AC) b.d. and famotidine 20 mg b.d. over 14 days of treatment.

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  • 1Oklahoma Foundation for Digestive Research, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA.



The onset of acid inhibition for proton pump inhibitors is slower than with H2RAs and generally considered to be at a steady-state after 5 days. Thus, little direct comparison data exists between H2RAs and proton pump inhibitors for gastric acid suppression on day 1 of therapy. Furthermore, the durability of their acid suppression has not been systematically compared.


To compare the effects of 20.6 mg omeprazole magnesium o.m. (Ome-Mg 20), famotidine 10 mg b.d. (Fam 10) and famotidine 20 mg b.d. (Fam 20) on intragastric pH on day 1 and throughout 14 days of dosing.


The study was a randomized, double-blind, three-dosing regimens, three-period crossover. Healthy adults with frequent heartburn (> or =2 days/week) underwent 24-h gastric pH monitoring on days 0 (baseline), 1, 3, 7 and 14.


Thirty-one subjects were included in the per-protocol analyses. On day 1, the mean percentage time pH > 4 (pH4%) was higher for Ome-Mg 20, 44.6%, than for Fam 10, 36.7% (P = 0.032), and not different from Fam 20, 46.9% (P = 0.541). The pH4% was higher for Ome-Mg 20 than either famotidine regimen on all subsequent monitoring days (P < 0.001). The 24-h area under the mean intragastric pH curve showed a similar pattern. Furthermore, after day 1, Ome-Mg 20 demonstrated an increasing and sustained effect in contrast to a decreasing effect for famotidine, consistent with H2RA tolerance.


Gastric acid suppression on Ome-Mg 20 mg o.m. over 14 days was comparable with Fam 10 mg b.d. or Fam 20 mg b.d. on day 1, and superior thereafter.

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