Isoxazoles. 8. Preformulation studies of an isoxazolylnaphthoquinone derivative

The degradation kinetics of 2-hydroxy-N-(3,4-dimethyl-5-isoxazolyl)-1,4-naphthoquinone 4-imine (1) in a 25% solution of ethyl alcohol in water has been studied. The rate constants were observed to follow pseudo-first-order kinetics in all cases. The pH-rate profile indicated a negligible decomposition at pH values higher than its pKa2 value [5.4 +/- 0.14 (*n = 6)]. Un-ionized 1 was subject to specific acid catalysis. The ionic strength did not affect the stability of the drug. These data can be used to develop a stable oral liquid dosage form of the drug.