EFFECT OF TIME AND CONCENTRATION UPON INTERACTION BETWEEN GENTAMICIN TOBRAMYCIN, NETILMICIN, OR AMIKACIN AND CARBENICILLIN OR TICARCILLIN

An aminoglycoside antibiotic and carbenicillin or ticarcillin are widely used in the treatment of patients with gram-negative bacillus infections. This study evaluated the effect of time upon in vitro interaction between mixtures of 4 aminoglycosides at 2 concentrations with carbenicillin or ticarcillin at 4 concentrations. By linear regression analysis, the inactivation of each aminoglycoside was shown to be directly proportional to the concentration of carbenicillin (P < 0.001). Inactivation was significantly (P < 0.01) greater for gentamicin and tobramycin than for amikacin or netilmicin at all carbenicillin concentrations. At carbenicillin concentrations of 300 and 600 .mu.g/ml, significantly (P < 0.005) less inactivation of amikacin occurred when compared to netilmicin. Ticarcillin produced a significant (P < 0.025) inactivation of gentamicin and tobramycin, with inactivation being directly proportional to ticarcillin concentration. No inactivation of amikacin or netilmicin activity occurred unless the ticarcillin concentration was 600 .mu.g/ml. No significant change in aminoglycoside activity occurred when stored with ticarcillin or carbenicillin at concentrations ranging from 100-600 .mu.g/ml at -70.degree. C for 56 days. When an aminoglycoside and carbenicillin or ticarcillin are indicated in patients with renal failure, this study supports the use of ticarcillin with amikacin or netilmicin.