Search

Colistin is a polymyxin and peptide antibiotic that can yield rapid bacterial killing, but also leads to resistance emergence. We aimed to develop a novel experimental and Quantitative and Systems Pharmacology approach to distinguish between inducible and non-inducible resistance. Viable count profiles for the total and less susceptible populations of Pseudomonas aeruginosa ATCC 27853 from static and dynamic in vitro infection models were simultaneously modeled. We studied low and normal initial inocula to distinguish between inducible and non-inducible resistance. A novel cutoff filter approach allowed us to describe the eradication and inter-conversion of bacterial populations. At all inocula, 4.84 mg/L of colistin (sulfate) yielded ≥4 log 10 killing, followed by >4 log 10 regrowth. A pre-existing, less susceptible population was present at standard but not at low inocula. Formation of a non-pre-existing, less susceptible population was most pronounced at intermediate colistin (sulfate) concentrations (0.9 to 5 mg/L). Both less susceptible populations inter-converted with the susceptible population. Simultaneously modeling of the total and less susceptible populations at low and standard inocula enabled us to identify the de novo formation of an inducible, less susceptible population. Inducible resistance at intermediate colistin concentrations highlights the importance of rapidly achieving efficacious polymyxin concentrations by front-loaded dosage regimens., Competing Interests: Declaration of Competing Interest J.L. and R.L.N. licensed their new-generation polymyxin molecules to Qpex Biopharma and Brii Biosciences. J.L. is Chief Executive Officer of Sliabx Pharmaceuticals and Cinfinno Biotech and holds equity in the companies. J.L. received grants, seminar honoraria, and consultation fees from Northern Antibiotics, Qpex Biopharma, Genentech, Healcare Pharmaceuticals, CTTQ, Aosaikang, Jiayou Medicine, MedCom, DanDi Bioscience, and Xellia ApS. J.B.B. is a consultant for Micurx Pharmaceutical Inc. All other authors declare no conflict of interest., (Copyright © 2023 American Pharmacists Association. Published by Elsevier Inc. All rights reserved.)

Acute exacerbations of chronic respiratory infections in patients with cystic fibrosis are highly challenging due to hypermutable Pseudomonas aeruginosa, biofilm formation and resistance emergence. We aimed to systematically evaluate the effects of intravenous versus inhaled tobramycin (TOB) with and without intravenous ceftazidime (CAZ). Two hypermutable P. aeruginosa isolates, CW30 (MIC CAZ , 0.5 mg/liter; MIC TOB , 2 mg/liter) and CW8 (MIC CAZ , 2 mg/liter; MIC TOB , 8 mg/liter), were investigated for 120 h in dynamic in vitro biofilm studies. Treatments were intravenous ceftazidime, 9 g/day (33% lung fluid penetration); intravenous tobramycin, 10 mg/kg of body every 24 h (50% lung fluid penetration); inhaled tobramycin, 300 mg every 12 h; and both ceftazidime-tobramycin combinations. Total and less susceptible planktonic and biofilm bacteria were quantified over 120 h. Mechanism-based modeling was performed. All monotherapies were ineffective for both isolates, with regrowth of planktonic (≥4.7 log 10 CFU/ml) and biofilm (>3.8 log 10 CFU/cm 2 ) bacteria and resistance amplification by 120 h. Both combination treatments demonstrated synergistic or enhanced bacterial killing of planktonic and biofilm bacteria. With the combination simulating tobramycin inhalation, planktonic bacterial counts of the two isolates at 120 h were 0.47% and 36% of those for the combination with intravenous tobramycin; for biofilm bacteria the corresponding values were 8.2% and 13%. Combination regimens achieved substantial suppression of resistance of planktonic and biofilm bacteria compared to each antibiotic in monotherapy for both isolates. Mechanism-based modeling well described all planktonic and biofilm counts and indicated synergy of the combination regimens despite reduced activity of tobramycin in biofilm. Combination regimens of inhaled tobramycin with ceftazidime hold promise to treat acute exacerbations caused by hypermutable P. aeruginosa strains and warrant further investigation.

Treatment of exacerbations of chronic Pseudomonas aeruginosa infections in patients with cystic fibrosis (CF) is highly challenging due to hypermutability, biofilm formation, and an increased risk of resistance emergence. We evaluated the impact of ciprofloxacin and meropenem as monotherapy and in combination in the dynamic in vitro CDC biofilm reactor (CBR). Two hypermutable P. aeruginosa strains, PAOΔ mutS (MIC of ciprofloxacin [MIC ciprofloxacin ], 0.25 mg/liter; MIC meropenem , 2 mg/liter) and CW44 (MIC ciprofloxacin , 0.5 mg/liter; MIC meropenem , 4 mg/liter), were investigated for 120 h. Concentration-time profiles achievable in epithelial lining fluid (ELF) following FDA-approved doses were simulated in the CBR. Treatments were ciprofloxacin at 0.4 g every 8 h as 1-h infusions (80% ELF penetration), meropenem at 6 g/day as a continuous infusion (CI) (30% and 60% ELF penetration), and their combinations. Counts of total and less-susceptible planktonic and biofilm bacteria and MICs were determined. Antibiotic concentrations were quantified by an ultrahigh-performance liquid chromatography photodiode array (UHPLC-PDA) assay. For both strains, all monotherapies failed, with substantial regrowth and resistance of planktonic (≥8 log 10 CFU/ml) and biofilm (>8 log 10 CFU/cm 2 ) bacteria at 120 h (MIC ciprofloxacin , up to 8 mg/liter; MIC meropenem , up to 64 mg/liter). Both combination treatments demonstrated synergistic bacterial killing of planktonic and biofilm bacteria of both strains from ∼48 h onwards and suppressed regrowth to ≤4 log 10 CFU/ml and ≤6 log 10 CFU/cm 2 at 120 h. Overall, both combination treatments suppressed the amplification of resistance of planktonic bacteria for both strains and of biofilm bacteria for CW44. The combination with meropenem at 60% ELF penetration also suppressed the amplification of resistance of biofilm bacteria for PAOΔ mutS Thus, combination treatment demonstrated synergistic bacterial killing and resistance suppression against difficult-to-treat hypermutable P. aeruginosa strains., (Copyright © 2020 American Society for Microbiology.)

Exacerbations of chronic Pseudomonas aeruginosa infections are a major treatment challenge in cystic fibrosis due to biofilm formation and hypermutation. We aimed to evaluate different dosage regimens of meropenem and tobramycin as monotherapies and in combination against hypermutable carbapenem-resistant P. aeruginosa A hypermutable P. aeruginosa isolate (meropenem and tobramycin MICs, 8 mg/liter) was investigated in the dynamic CDC biofilm reactor over 120 h. Regimens were meropenem as the standard (2 g every 8 h, 30% epithelial lining fluid [ELF] penetration) and as a continuous infusion (CI; 6 g/day, 30% and 60% ELF penetration) and tobramycin at 10 mg/kg of body weight every 24 h (50% ELF penetration). The time courses of totally susceptible and less-susceptible bacteria and MICs were determined, and antibiotic concentrations were quantified by liquid chromatography-tandem mass spectrometry. All monotherapies failed, with the substantial regrowth of planktonic (>6 log 10 CFU/ml) and biofilm (≥6 log 10 CFU/cm 2 ) bacteria occurring. Except for the meropenem CI (60% ELF penetration), all monotherapies amplified less-susceptible planktonic and biofilm bacteria by 120 h. The meropenem standard regimen with tobramycin caused initial killing followed by considerable regrowth with resistance (meropenem MIC, 64 mg/liter; tobramycin MIC, 32 mg/liter) for planktonic and biofilm bacteria. The combination containing the meropenem CI at both levels of ELF penetration synergistically suppressed the regrowth of total planktonic bacteria and the resistance of planktonic and biofilm bacteria. The combination with the meropenem CI at 60% ELF penetration, in addition, synergistically suppressed the regrowth of total biofilm bacteria. Standard regimens of meropenem and tobramycin were ineffective against planktonic and biofilm bacteria. The combination with meropenem CI exhibited enhanced bacterial killing and resistance suppression of carbapenem-resistant hypermutable P. aeruginosa ., (Copyright © 2019 American Society for Microbiology.)

We described bacterial killing and resistance emergence at various fixed concentrations of meropenem and piperacillin/tazobactam against Pseudomonas aeruginosa and Escherichia coli. Time-kill studies were conducted utilizing nine isolates and a large range of concentrations. Within each strain and antibiotic, initial killing was similar, with concentrations ≥2×MIC. At many (strain-specific) concentrations causing substantial initial killing, regrowth occurred at 24-48h. For remaining concentrations, growth typically remained suppressed (<5-log 10 cfu/mL). The concentrations of meropenem required to suppress regrowth ranged from 2-8×MIC for P. aeruginosa and 2-64×MIC for E. coli. For piperacillin/tazobactam, the equivalent concentrations ranged from 8-16×MIC for P. aeruginosa and 4-16×MIC for E. coli. The number of less-susceptible bacteria increased with rising concentrations before decreasing at even higher concentrations. Suppression of regrowth and resistance was substantially improved with higher concentrations (typically ≥8×MIC), suggesting a benefit of higher β-lactam concentrations beyond those required for maximum initial killing., (Copyright © 2018. Published by Elsevier Inc.)

Critically ill patients frequently have substantially altered pharmacokinetics compared to non-critically ill patients. We investigated the impact of pharmacokinetic alterations on bacterial killing and resistance for commonly used meropenem dosing regimens. A Pseudomonas aeruginosa isolate (MIC meropenem 0.25 mg/liter) was studied in the hollow-fiber infection model (inoculum ∼10 7.5 CFU/ml; 10 days). Pharmacokinetic profiles representing critically ill patients with augmented renal clearance (ARC), normal, or impaired renal function (creatinine clearances of 285, 120, or ∼10 ml/min, respectively) were generated for three meropenem regimens (2, 1, and 0.5 g administered as 8-hourly 30-min infusions), plus 1 g given 12 hourly with impaired renal function. The time course of total and less-susceptible populations and MICs were determined. Mechanism-based modeling (MBM) was performed using S-ADAPT. All dosing regimens across all renal functions produced similar initial bacterial killing (≤∼2.5 log 10 ). For all regimens subjected to ARC, regrowth occurred after 7 h. For normal and impaired renal function, bacterial killing continued until 23 to 47 h; regrowth then occurred with 0.5- and 1-g regimens with normal renal function ( fT >5×MIC = 56 and 69%, fC min /MIC < 2); the emergence of less-susceptible populations (≥32-fold increases in MIC) accompanied all regrowth. Bacterial counts remained suppressed across 10 days with normal (2-g 8-hourly regimen) and impaired (all regimens) renal function ( fT >5×MIC ≥ 82%, fC min /MIC ≥ 2). The MBM successfully described bacterial killing and regrowth for all renal functions and regimens simultaneously. Optimized dosing regimens, including extended infusions and/or combinations, supported by MBM and Monte Carlo simulations, should be evaluated in the context of ARC to maximize bacterial killing and suppress resistance emergence., (Copyright © 2017 American Society for Microbiology.)

Background: Pathophysiological changes in critically ill patients can cause severely altered pharmacokinetics and widely varying antibiotic exposures. The impact of altered pharmacokinetics on bacterial killing and resistance has not been characterized in the dynamic hollow-fibre in vitro infection model (HFIM)., Methods: A clinical Pseudomonas aeruginosa isolate (piperacillin MIC 4 mg/L) was studied in the HFIM (inoculum ∼10(7) cfu/mL). Pharmacokinetic profiles of three piperacillin dosing regimens (4 g 8-, 6- and 4-hourly, 30 min intravenous infusion) as observed in critically ill patients with augmented renal clearance (ARC), normal renal function or impaired renal function (creatinine clearances of 250, 110 or 30 mL/min, respectively) were simulated over 7 days. The time courses of total and less-susceptible populations and MICs were determined. Mechanism-based modelling was performed in S-ADAPT., Results: For all regimens with ARC and regimens with 8- or 6-hourly dosing with normal renal function, initial killing of ≤∼2 log10 was followed by regrowth to 10(8)-10(9) cfu/mL at 48 h. For 8- and 6-hourly dosing at normal renal function, the proportion of less-susceptible colonies increased ∼10-100-fold above those in ARC and control arms. Regimens achieving an fCmin of ≥5× MIC resulted in bacterial killing of 3-4 log10 without regrowth and suppressed less-susceptible populations to ≤∼2 log10. The mechanism-based model successfully quantified the time course of bacterial growth, killing and regrowth., Conclusions: Only high piperacillin concentrations prevented regrowth of P. aeruginosa. Individualized dosing regimens that account for altered pharmacokinetics and aim for higher-than-standard antibiotic exposures to achieve an fCmin of ≥5× MIC were required to maximize bacterial killing and suppress emergence of resistance., (© The Author 2016. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.)