Post-antibiotic effect of isepamicin compared to that of other aminoglycosides

Isepamicin is a new aminoglycoside drug derived from gentamicin, which is more stable than other aminoglycosides to inactivating enzymes and experimentally is less nephrotoxic than gentamicin or amikacin. In this work a comparative study was carried out on the antibacterial activity (MIC and lethality curves) and the post-antibiotic effect (PAE) of different concentrations of isepamicin, netilmicin and gentamicin on pure cultures of S. aureus and E. coli. The MIC and curves of lethality were determined by conventional methods. The PAE was determined after exposure of the bacterial culture to the antimicrobial one for 1 h at 37 degrees C in a bath with stirring. Elimination of the drug was made by the dilution method. Isepamicin was found to have a MIC four times greater than netilmicin and gentamicin. Its activity over time was similar to that exhibited by other aminoglycosides. At concentrations higher than the MIC, a bactericidal effect was found with the three antibiotics, although isepamicin produced it at lower concentrations. The post-antibiotic effect induced by isepamicin, the same as that of netilmicin and gentamicin, was extensive and depended on the concentration and the strain used. Isepamicin shows antibiotic activity over time and a PAE similar to the other aminoglycosides tested but, unlike them, it has a faster activity, less toxicity and better resistance to inactivating enzymes. For this reason it makes a considerable contribution to antibacterial therapies in severe conditions, including immunodepressed patients who require long-term treatment.