[Influence of urine pH and cations on antimicrobial activities of penems]

We compared the antimicrobial activities of penems in human urine with those in Mueller-Hinton broth in order to clarify the usefulness of penems for urinary tract infections. Furthermore, we also investigated the influence of urine components, such as pH, magnesium concentration and calcium concentration, on the antimicrobial activities of penems. Three penems, i.e., imipenem, panipenem and meropenem were employed. And two bacterial strains, i.e., Escherichia coli NIHJ JC-2 and Pseudomonas aeruginosa 18s, were tested. There was no significant difference in MBCs between human urine and Mueller-Hinton broth against E. coli. However, MBCs of penems in human urine was lower than those in Mueller-Hinton broth against P. aeruginosa. On the other hand, MBCs of penems against these two strains were low when urine pH was high or urine calcium concentration was low. No influence of urine magnesium concentration on MBCs of penems was seen. From these results, it was suggested that we should measure the antimicrobial activities of penems not only in Mueller-Hinton broth, but also in human urine, when we administer penems to patients with urinary tract infections. And we should foresee the clinical effects of penems against urinary tract infections paying attention to urine pH of the patients.