Solid state properties of an oral iron chelator, 1,2-dimethyl-3-hydroxy-4-pyridone, and its acetic acid solvate. I: Physicochemical characterization, intrinsic dissolution rate, and solution thermodynamics.

1,2-Dimethyl-3-hydroxy-4-pyridone (1), a crystalline oral iron chelator, forms an acetic acid solvate (2) on recrystallization from acetic acid and carbon tetrachloride. Compound 2 forms compact prisms, and 1 forms needles from water (mp 274 degrees C). The X-ray powder diffraction patterns of 1 and 2 differ, indicating distinct solid phases. Compound 2 has an extra DSC endotherm at 82 degrees C that is accompanied by a weight loss of 29% in TGA, corresponding to the desolvation of a 1:1 acetic acid solvate. Comparison of the solid-state 13C NMR of 1 and 2 revealed two additional peaks for 2 at 20.3 and 175.6 ppm, characteristic of -CH3 and -COOH, respectively, of acetic acid. The integrated intensities confirmed the 1:1 stoichiometry between 1 and acetic acid. However, 2 underwent desolvation in air at 25 degrees C as suggested by a change in its appearance to opaque crystals and as confirmed by X-ray powder diffraction, DSC, and TGA. Desolvation of 2 at 25 degrees C was a zero-order process with a rate constant of 6.9 mumol.h-1. X-ray powder diffraction showed that crystals or compacted discs of 1 are converted to 2 in contact with glacial acetic acid (A), whereas crystals or discs of 2 are converted to 1 in contact with water. The intrinsic dissolution rate (J) and the apparent solubility (Cs) of compacted discs of 1 and 2 were measured in water at 25 degrees C, and the following relations were determined: J(2)/J(1) = 1.39 and Cs(2)/Cs(1) = 1.70.(ABSTRACT TRUNCATED AT 250 WORDS)