T. Morimura et al., DEGRADATION KINETICS OF THE NEW ANTIBACTERIAL FLUOROQUINOLONE DERIVATIVE, ORBIFLOXACIN, IN AQUEOUS-SOLUTION, Chemical and Pharmaceutical Bulletin, 43(6), 1995, pp. 1052-1054
The degradation kinetics of orbifloxacin imethyl-1-piperazinyl)-4-oxoq
uinoline-3-carboxylic acid] was investigated as a function of pH (1.5-
10.5), temperature (100-120 degrees C) and buffer concentration (0.05-
0.2 M) by means of high-performance liquid chromatography. The degrada
tion of orbifloxacin in aqueous solution followed apparent first-order
kinetics under all experimental conditions, No appreciable effect of
buffer on the degradation of orbifloxacin was observed for any of the
buffer species used in this study, The log k-pH profiles indicated spe
cific-acid and specific-base catalyses and there were inflection point
s near pH 6 and 9 corresponding to the pK(a1) and pK(a2) values, From
the Arrhenius plots, the activation energies for k(H)', k(H2O)', k(H2O
), k(H2O)'' and k(OH)'' were found to be 31.9, 36.9, 23.5, 26.5 and 19
.0 kcal/mol, respectively, Arrhenius data obtained from this study sho
wed that the degradation of orbifloxacin at room temperature was negli
gible at all pH values studied conditions (pH 1.5-10.5),