Efficacy of meropenem extended infusion vs intermittent bolus monotherapy and in combination with colistin against Pseudomonas aeruginosa biofilm.

Introduction: Device-related infections are difficult to treat due to biofilms. In this setting, optimizing antibiotic efficacy is difficult as most pharmacokinetic/pharmacdynamic (PK/PD) studies have been performed on planktonic cells, and therapies are limited when multi-drug-resistant bacteria are involved. This study aimed to analyse the PK/PD indices of meropenem predicting anti-biofilm efficacy against meropenem-susceptible and meropenem-resistant strains of Pseudomonas aeruginosa.

Materials And Methods: Pharmacodynamics of meropenem dosages mimicking those of clinical practice (intermittent bolus of 2 g every 8 h; extended infusion of 2 g over 4 h every 8 h), with and without colistin, were evaluated with the CDC Biofilm Reactor in-vitro model for susceptible (PAO1) and extensively-drug-resistant (XDR-HUB3) P. aeruginosa. Efficacy was correlated with the PK/PD indices for meropenem.

Results: For PAO1, both meropenem regimens were bactericidal, with higher killing for extended infusion [∆log colony-forming units (CFU)/mL 54-0h=-4.66±0.93 for extended infusion vs ∆log CFU/mL 54-0h=-3.4±0.41 for intermittent bolus; P<0.001]. For XDR-HUB3, the intermittent bolus regimen was non-active, but extended infusion showed bactericidal effect (∆log CFU/mL 54-0h=-3.65±0.29; P<0.001). Time above minimum inhibitory concentration (f%T) had the best correlation with efficacy for both strains. The addition of colistin always improved meropenem activity, and resistant strains did not emerge.

Conclusion: f%T was the PK/PD index that best correlated with the anti-biofilm efficacy of meropenem; it was better optimized when using the extended infusion regimen, allowing recovery of bactericidal activity in monotherapy, including activity against meropenem-resistant P. aeruginosa. Combining meropenem by extended infusion with colistin offered the most effective therapy for both strains. Optimizing meropenem dosing by extended infusion should be encouraged when treating biofilm-related infections.