BIavailability of metronidazole from sugar-coated tablets in humans. I. Effect of gastric acidity and correlation with in vitro dissolution rate

Abstract The bioavailability of five commercial sugar-coated metronidazole tablets was studied. The dissolution rates of the five test tablets were determined by rotating flask, oscillating basket, rotating basket and paddle methods at pH values of 1.2, 3, 4, 5, 6 and 7.2. Though metronidazole dissolves easily in water, with a solubility of 11.6 mg/ml at a pH of 7, some sugar-coated tablets showed very slow dissolution at a pH of 5 or 7.2, in spite of very rapid dissolution at a pH of 1.2. This may be due to the pH-dependent dissolution of their water-proof coatings. The bioavailability of metronidazole from three tablets showing extremely slow dissolution at pH 5 or 7.2 varied significantly between human subjects having high and low gastric acidity. However, correlation between bioavailability and dissolution rate were shown to be poor.