Propiedades microbiológicas, clasificación y relación estructura-actividad de cefalosporinas e importancia de las cefalosporinas de cuarta generación

Abstract

The cephalosporins are one of the most important types of -lactam antibiotics. There are various classifications of these molecules, but the most frecuently used classifies them according to their structures, microbiological properties and historical development: first to fourth generation cephalosporins. Third generation cephalosporins have been extensively used, but the emergence of bacterial resistance, mainly as a consecuence of chromosomal and plasmidial production of -lactamases has limited the use of these antibiotics. Fourth generation cephalosporins are characterized by the presence of a cuaternary nitrogen in C3; mantaining the methoxyimino aminothiazolyl in C7. Fourth generation cephalosporins display a high capacity of intracellular penetration through the external membranes of Gram negative rods and a low affinity to enzymes that degrade third generation cephalosporins. Cefepime, a fourth generation cephalosporin, has shown more inhibitory activity against chilean strains of Klebsiella pneumoniae and Escherichia coli that produce extended-spectrum -lactamases, than cefotaxime and ceftazidime.