Des-, syn- and anti-oxyimino-delta 3-cephalosporins. Intrinsic reactivity and reaction with RTEM-2 serine beta-lactamase and D-alanyl-D-alanine-cleaving serine and Zn2+-containing peptidases

Newly identified degradation products of ceftiofur and cephapirin impact the analytical approach for quantitative analysis of kidney

This paper describes our research on the degradation of ceftiofur and cephapirin at physiological temperatures in kidney extract and in alkaline and acidic solution, conditions that regularly occur during sample preparation. Degradation products were identified using LC-ToF/MS, NMR and microbiological techniques. Additionally kinetics of the degradation processes were studied. A slight instability of cephapirin and desfuroylceftiofur was observed at elevated temperatures. Ceftiofur and cephapirin degraded immediately and completely in an alkaline environment, resulting in inactive degradation products. Ceftiofur and cephapirin also degraded immediately and completely in kidney extract resulting in both formerly reported metabolites as well as not previously reported products. Our research shows that conditions often occurring during the analysis of ceftiofur or cephapirin result in rapid degradation of both compounds. From this it is concluded that underestimation of the determined amounts of ceftiofur and cephapirin is likely to occur. Therefore, a new approach is needed for the analysis of both compounds newly identified degradation products.

Photodegradation paths of cefotaxime

The degradation kinetics of cefotaxime sodium salt in aqueous solution, under UV light at 254 nm, was investigated by HPLC and antibiotic activity. This degradation is the result of two competitive processes, an isomerization and a photolysis. This study is mostly about the isomerization step. The measured quantum yields for the cefotaxime to its anti-isomer and anti-isomer to cefotaxime isomerizations are, respectively, 0.10 and 0.12. A photostationary state characterized by an anti:syn ratio of 1.2 is obtained after 30 min of irradiation. The competitive photolysis, which actually consists of at least two processes (one on the delta 3-cephem ring and the second on the methoxyimino group), leads to an intense yellowing of the solution corresponding to the destruction of the molecule. The comparative evolution of the absorption spectra, under irradiation at 254 nm, of cefotaxime, thiazoximic acid, and 7-aminocephalosporanic acid shows that it is the delta 3-cephem ring photolysis which gives the yellow color. The major conclusion of this work is to call attention to the photoisomerization step which leads efficiently to the inactive anti-isomer, without giving any visible notice of degradation. Such a process is to be expected in all antibiotics containing an alkoxyimino linkage on the C-7 substitution.

Lack of relevance of kinetic parameters for exocellular DD-peptidases to cephalosporin MICs

MICs of a set of cephalosporins against a variety of gram-positive and gram-negative pathogens showed no strong correlations with the rate at which these inhibitors acylate or are deacylated by beta-lactam-sensitive DD-peptidases excreted by Streptomyces sp. strain R61 and Actinomadura sp. strain R39.