Dissolution Behavior of Piretanide Polymorphs at Various Temperatures and pHs

We investigated the dissolution behavior of piretanide polymorphs, forms A and B in buffers from pH 1.0-7.0 at a range of temperatures (30-45°C) by a dispersed-amount method. These polymorphs were also tested by the stationary-disk method in pH 5 buffer at 30-45°C. The dissolution of forms A and B compressed into tablets with excipients was also tested in a pH 5 buffer at 37°C by the paddle method.The solubility and the initial dissolution rate of forms A and B were temperature dependent at pH 5. Form B showed higher solubility and a faster initial dissolution rate than form A at various temperatures in pH 5. The solubility of form B calculated from the initial dissolution rate determined by the stationary-disk and the conventional dispersed-amount methods agreed well. Tablets of form B dissolved more quickly than of those form A. The solubility of the two forms suggest that a difference in their initial dissolution rates affect the bioavailability of piretanide preparations.