Diclofenac salts. I. Fractal and thermal analysis of sodium and potassium diclofenac salts

Sodium and potassium diclofenac salts form hydrates when crystallized from water; the sodium salt contains four crystallization water molecules, while the potassium salt precipitates as a dihydrate. Crystallization from organic solvents occurs with a change of the crystal habit. The fractal. dimension of the particle surface of both salts obtained from water is low and is in agreement with the formation of smooth and regular surfaces during crystallization. The fractal dimension for dissolution is relatively high and comparable for hydrate and anhydrate forms of both salts, and the result was interpreted as being due to the surfactant behavior of diclofenac anions. Thermograms of both salts show a couple of endotherms in the range 30-100 degreesC, which disappear when the salts have been previously heated at 100 degreesC, but slowly reappear when the anhydrate forms are stored in a humid environment. Both salts present a complex exotherm of decomposition at 284 and 314 degreesC, respectively. The results are briefly discussed with regard to the formulations of the anti-inflammatory agent diclofenac. (C) 2001 Wiley-Liss, Inc, and the American Pharmaceutical Association J Pharm Sci 90:2049-2057, 2001.