Solid-state stability studies of faropenem based on chromatography, spectroscopy and theoretical analysis.

ABSTRACT

AIM: The purpose of this study was to investigate the stability of faropenem in solid state. RESULTS: The kinetic and thermodynamic parameters of degradation of faropenem were studied using an RP-HPLC method while the changes of spectral properties were investigated using derivative UV and FT-IR. Quantum-chemical calculations, based on the density functional theory, were carried out to support the estimation of the intra-ring stresses of faropenem and for theoretical interpretation of the spectra. The degradation of faropenem was a first-order reaction depending on the substrate concentration at an increased relative humidity and in dry air. The dependence ln k = f(1/T) became the ln k = (2.03 ± 3.22) × 10(4)-(9761 ± 3052)(1/T) in dry air and ln k = (1.25 ± 0.22) × 10(5)-(9004 ± 3479)(1/T ) at 90.0% RH. The thermodynamic parameters Ea, ΔH(≠a), and ΔS(≠a) of the degradation of faropenem were calculated. The dependence ln k = f(RH%) assumed the form ln k = (7.58 ± 1.88) × 10(-2) (RH%) - (5.90 ± 3.90) × 10(-8). CONCLUSIONS: Stability studies of faropenem showed that the fusion of ß-lactam and thiazolidine rings reduces the intra-ring stress, leading to a lower susceptibility to degradation in dry air and at increased RH.