Kinetic and thermodynamic analysis of degradation of doripenem in the solid state

The kinetic and thermodynamic parameters of degradation of doripenem were studied using a high‐performance liquid chromatography method. In dry air, the degradation of doripenem was a first‐order reaction depending on the substrate concentration. At increased relative air humidity, doripenem was degraded according to the autocatalysis kinetic model. The dependence ln k = f 1/ T ) was described by the equations ln k = 5.10 ± 13.06 − (7576 ± 4939)(1/ T ) in dry air and ln k = 46.70 ± 22.44 − (19,959 ± 8031)(1/ T ) at 76.4% relative humidity (RH). The thermodynamic parameters E a , Δ H ≠a , and Δ S ≠a of the degradation of doripenem were calculated. The dependence ln k = f (RH%) was described by the equation ln k = (0.155 ± 0.077) × 10 −1 (RH%) − (3.45 ± 21.8) × 10 −10 . © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 722–728, 2012