The lack of inactivation of tobramycin by cefazolin, cefamandole, and moxalactam in vitro

We examined the effects of mixing tobramycin with three cephalosporins, cefazolin, cefamandole, and moxalactam. Each cephalosporin was prepared from standard powder and diluted with human serum to concentrations of 50, 250, and 500 micrograms/ml and added to 10 micrograms/ml of tobramycin in human serum. Temperature environments of 4 degrees C (refrigeration), 24 degrees C (room temperature), and 37 degrees C (body temperature) were used and sampled at 0 hours (control), and at 8, 24, and 48 hours. The results indicated no inactivation of tobramycin by any of the cephalosporins, regardless of temperature, concentration, or contact time. These results indicate that significant inactivation of tobramycin does not occur when it is combined in vitro with moxalactam, cefamandole, or cefazolin.