Bioavailability of Pyridoxal Phosphate from Enteric-Coated Tablets. II. Effects of Gastric Acidity of Humans

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The relationship between the gastric acidity of subjects and the bioavailability of pyridoxal phosphate from commercial enteric-coated tablets having various values of apparent critical pH for dissolution (above which the coated films disintegrate within 3h) was studied. The tablet with an apparent critical dissolution pH of 5.5 appeared not to disintegrate in the stomach even in subjects with anacidity, and the bioavailability was not affected by the gastric acidity of the subjects. However, the bioavailability of the tablet with an apparent critical dissolution pH of 6.6 and a short lag for dissolution at that pH did depend on the gastric acidity of the subjects, and the higher the gastric acidity, the more slowly was the drug absorbed. On the other hand, the enteric-coated tablet with an apparent critical dissolution pH of 4.5 might be subject to disintegration in the stomach of subjects with anacidity.