Ticarcillin-tobramycin-rifampin: in vitro synergy of the triplet combination against Pseudomonas aeruginosa.
MICs of ticarcillin, tobramycin, and rifampin alone and in combination were determined by a three-dimensional checkerboard method for 33 isolates of Pseudomonas aeruginosa. Twenty-nine of 33 isolates were affected synergistically (FIC index less than 1.0) by the combination of ticarcillin-tobramycin, including 13 of the 16 isolates resistant to ticarcillin and/or tobramycin alone. However, despite fulfilling the criteria for synergy, the MIC of the ticarcillin and/or tobramycin when in combination still exceeded attainable serum concentrations for 12 of the 13 resistant isolates. When rifampin was added to ticarcillin-tobramycin, a synergistic interaction was observed for all 33 isolates. Furthermore, of the 16 isolates resistant to ticarcillin and/or tobramycin, eight were inhibited by attainable concentrations of all three antibiotics in combination. If these results can be confirmed in the clinical situation, application of the three-drug combination of ticarcillin-tobramycin-rifampin might improve survival in selected patients with serious P. aeruginosa infections.
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D004338:Drug Combinations; D004357:Drug Synergism; D008826:Microbial Sensitivity Tests; D010406:Penicillins / Q000494:pharmacology*; D011550:Pseudomonas aeruginosa / Q000187:drug effects*; D012293:Rifampin / Q000494:pharmacology*; D013982:Ticarcillin / Q000494:pharmacology*; D014031:Tobramycin / Q000494:pharmacology*
D000900:Anti-Bacterial Agents; D004338:Drug Combinations; D010406:Penicillins; D013982:Ticarcillin; D012293:Rifampin; D014031:Tobramycin