OBJECTIVETo evaluate the antibacterial activity of Ciprofloxacin, Amikacin in combination with beta-lactams against Pseudomonas aeruginosa strains in vitro, to optimize treatment regime for antibiotics on the basis of pharmacokinetics (PK)/pharmacodynamics (PD) and drug sensitivity tests. Methods With checkerboard titration method, the minimal inhibitory concentrations (MIC) of a combination of antibiotics in different concentrations for 33 clinically isolated Pseudomonas aeruginosa strains were determined by broth dilution. Fractional inhibitory concentrations (FIC) were calculated for judging synergic effect of antibiotics.

RESULTSThe combination of Amikacin and Ceftazidime showed synergic effects (accounting for 57.6%). The combinations of Ciprofloxacin with Ceftazidime, Cefepime, Imipenem/Cilastatin, Meropenem showed synergic or additive effect. In the study with PK/PD, C(max)/MIC was the principal parameters for evaluation of aminoglycoside and fluoroquinolone antibiotics, while T > MIC was the principal parameter to be used to evaluate beta-lactams antibiotics.

CONCLUSIONWhen antibiotics are used in combination, MICs can be reduced significantly and antibacterial activities are enhanced remarkably. The combination of antibiotics results mainly in synergic or additive effect, and no inhibitory effect is observed. PK/PD analysis plays an important role in planning optimal combination regime to raise clinical efficacy.