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 extensivelydrug-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 10 colony-forming units (CFU)/mL 54-0h= -4.66 +/- 0.93 for extended infusion vs log 10 CFU/mL 540h =-3.4 +/- 0.41 for intermittent bolus; P<0.001]. For XDR-HUB3, the intermittent bolus regimen was nonactive, but extended infusion showed bactericidal effect (log 10 CFU/mL 54-0h= -3.65 +/- 0.29; P<0.001). Time above minimum inhibitory concentration (f%T >MIC) 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 >MIC 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. (c) 2023ElsevierLtdandInternationalSocietyofAntimicrobialChemotherapy. All rights reserved.