Human-simulated unbound plasma convergences of I/R at 1.25 g each 6 (h), colistin at 360 mg day by day, and amikacin at 25 mg/kg every day were replicated alone and in blend against six imipenem-nonsusceptible P. aeruginosa disengages in an in vitro pharmacodynamic model over 24 h. Resistant subpopulations were observed after 24 h in 1, 4, and 3 I/R-, colistin-, and amikacin-exposed isolates, respectively. For I/R alone, the mean reductions in CFU ± the standard errors by 24 h were −2.52 ± 0.49, −1.49 ± 0.49, −1.15 ± 0.67, and −0.61 ± 0.10 log10 CFU/ml against isolates with MICs of 1/4, 2/4, 4/4, and 8/4 μg/ml, respectively. Against these six multidrug-resistant P. aeruginosa, I/R alone achieved significant CFU reductions against I/R-susceptible isolates. No resistant subpopulations were observed during I/R and colistin combination studies, and when added to amikacin, I/R prevented the emergence of amikacin resistance. Therefore as a conclusion we can say that combinations of I/R plus colistin resulted in additivity or synergy against some P. aeruginosa, whereas the addition of amikacin did not provide further antibacterial efficacy against these isolates.

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