[Differences in the release of omeprazole in 4 commercial preparations: influence of pH and ionic concentration]

The influence of exposition to different ionic concentrations and pH values on the subsequent in vitro dissolution of omeprazole at pH 6.8 was studied in four enteric-coated commercial formulations. Assays were done using an experimental protocol similar to that recommended in Delayed-Release (Enteric Coated) Articles-General Drug Release Standards (USP 23) slightly modified to achieve similar pH values to commonly observed in patients under omeprazole treatment. Omeprazole capsules were exposed during 1 or 2 hours to four different pH values: 4.8, 5.0, 5.2, and 5.4 and two NaCl concentrations: 75 and 225 mM. After that, dissolution tests at pH 6.8 were performed. Three formulations (Emeprotón, Pepticum and Ulceral) released different percents of the encapsulated dose at the above acidic mediums and, consequently, the omeprazole dissolved underwent a remarkable degradation. The drug contained in the enteric-coated granules of Losec was not released and therefore the amount of omeprazole dissolved at pH 6.8 from Losec capsules was higher than the obtained with the other three preparations tested.