Individual Components of Polymyxin B Modeled via Population Pharmacokinetics to Design Humanized Dosage Regimens for a Bloodstream and Lung Infection Model in Immune-Competent Mice

An integrative and translational PK/PD modelling approach to explore the combined effect of polymyxin B and minocycline against Klebsiella pneumoniae

OBJECTIVES

To expand a translational pharmacokinetic-pharmacodynamic (PK/PD) modelling approach for assessing the combined effect of polymyxin B and minocycline against Klebsiella pneumoniae.

METHODS

A PK/PD model developed based on in vitro static time-kill experiments of one strain (ARU613) was first translated to characterize that of a more susceptible strain (ARU705), and thereafter to dynamic time-kill experiments (both strains) and to a murine thigh infection model (ARU705 only). The PK/PD model was updated stepwise using accumulated data. Predictions of bacterial killing in humans were performed.

RESULTS

The same model structure could be used in each translational step, with parameters being re-estimated. Dynamic data were well predicted by static-data-based models. The in vitro/in vivo differences were primarily quantified as a change in polymyxin B effect: a lower killing rate constant in vivo compared with in vitro (concentration of 3 mg/L corresponds to 0.05/h and 57/h, respectively), and a slower adaptive resistance rate (the constant in vivo was 2.5% of that in vitro). There was no significant difference in polymyxin B-minocycline interaction functions. Predictions based on both in vitro and in vivo parameters indicated that the combination has a greater-than-monotherapy antibacterial effect in humans, forecasting a reduction of approximately 5 and 2 log10 colony-forming units/mL at 24 h, respectively, under combined therapy, while the maximum bacterial load was reached in monotherapy.

CONCLUSIONS

This study demonstrated the utility of the PK/PD modelling approach to understand translation of antibiotic effects across experimental systems, and showed a promising antibacterial effect of polymyxin B and minocycline in combination against K. pneumoniae.

Comparing ceftazidime/avibactam and polymyxin B for treating carbapenem-resistant organisms infections: A propensity score-matched retrospective cohort study

BACKGROUND AND AIM

There are limited comparative studies of ceftazidime/avibactam (CAZ/AVI) vs. polymyxin B (PMB) for carbapenem-resistant organisms (CRO) infections. The aim of this study was to compare the efficacy and safety of CAZ/AVI and PMB in treating CRO infections.

METHODS

This single-centre, retrospective cohort study with propensity score-matching (PSM) involved adult patients with CRO infections. Patients who received the CAZ/AVI-based regimen were included in the cohort group; those prescribed with the PMB-based regimen were included in the control group. The primary outcome was 28-day all-cause mortality.

RESULTS

Among 298 eligible patients, 96 patients in each group were included in the PSM cohort. The CAZ/AVI group showed no improvement in 28-day or 14-day all-cause mortality, nor in 14-day clinical response, compared to the PMB group. However, the CAZ/AVI-based regimen was associated with higher 14-day clinical response rates than the PMB-based regimen in subgroups with carbapenem-resistant Pseudomonas aeruginosa (CRPA) infections and monotherapy. The CAZ/AVI group achieved greater CRO eradication than the PMB group (crude odds ratio [OR], 1.658; 95% confidence interval [CI], 1.108-2.480; P = 0.014; adjusted OR, 1.718; 95% CI, 1.055-2.798; P = 0.030). This advantage in CRO eradication with CAZ/AVI was consistent in most subgroups, including septic shock, bloodstream infection and lower respiratory tract infection. The CAZ/AVI and PMB groups had comparable nephrotoxicity (crude OR, 0.577; 95% CI, 0.306-1.089; P = 0.090; adjusted OR, 0.741; 95% CI, 0.361-1.521; P = 0.414).

CONCLUSION

CAZ/AVI-based and PMB-based regimens demonstrated similar clinical efficacy and nephrotoxicity in treating CRO infections. However, CAZ/AVI was superior to PMB in CRO eradication and treating CRPA infections. CAZ/AVI monotherapy was more effective than PMB monotherapy for CRO infections.

TRIAL REGISTRATION

ChiCTR2300078790 prospectively registered on 19 Dec 2023 (https://www.chictr.org.cn).

Polymyxins retain in vitro activity and in vivo efficacy against "resistant" Acinetobacter baumannii strains when tested in physiological conditions

The emergence of plasmid-mediated resistance threatens the efficacy of polymyxins as the last line of defense against pan-drug-resistant infections. However, we have found that using Mueller-Hinton II (MHII), the standard minimum inhibitory concentration (MIC) medium, results in MIC data that are disconnected from in vivo treatment outcomes. We found that culturing putative colistin-resistant Acinetobacter baumannii clinical isolates, as defined by MICs of >2 mg/L in standard MHII testing conditions, in bicarbonate-containing media reduced MICs to the susceptible range by preventing colistin resistance-conferring lipopolysaccharide modifications from occurring. Furthermore, the lower MICs in bicarbonate-containing media accurately predicted in vivo efficacy of a human-simulated dosing strategy of colistin and polymyxin B in a lethal murine infection model for some polymyxin-resistant A. baumannii strains. Thus, current polymyxin susceptibility testing methods overestimate the contribution of polymyxin resistance-conferring mutations and incorrectly predict antibiotic activity in vivo. Polymyxins may remain a viable therapeutic option against Acinetobacter baumannii strains heretofore determined to be "pan-resistant."

Population pharmacokinetics and humanized dosage regimens matching the peak, area, trough, and range of amikacin plasma concentrations in immune-competent murine bloodstream and lung infection models

Amikacin is an FDA-approved aminoglycoside antibiotic that is commonly used. However, validated dosage regimens that achieve clinically relevant exposure profiles in mice are lacking. We aimed to design and validate humanized dosage regimens for amikacin in immune-competent murine bloodstream and lung infection models of Acinetobacter baumannii. Plasma and lung epithelial lining fluid (ELF) concentrations after single subcutaneous doses of 1.37, 13.7, and 137 mg/kg of body weight were simultaneously modeled via population pharmacokinetics. Then, humanized amikacin dosage regimens in mice were designed and prospectively validated to match the peak, area, trough, and range of plasma concentration profiles in critically ill patients (clinical dose: 25-30 mg/kg of body weight). The pharmacokinetics of amikacin were linear, with a clearance of 9.93 mL/h in both infection models after a single dose. However, the volume of distribution differed between models, resulting in an elimination half-life of 48 min for the bloodstream and 36 min for the lung model. The drug exposure in ELF was 72.7% compared to that in plasma. After multiple q6h dosing, clearance decreased by ~80% from the first (7.35 mL/h) to the last two dosing intervals (~1.50 mL/h) in the bloodstream model. Likewise, clearance decreased by 41% from 7.44 to 4.39 mL/h in the lung model. The humanized dosage regimens were 117 mg/kg of body weight/day in mice [administered in four fractions 6 h apart (q6h): 61.9%, 18.6%, 11.3%, and 8.21% of total dose] for the bloodstream and 96.7 mg/kg of body weight/day (given q6h as 65.1%, 16.9%, 10.5%, and 7.41%) for the lung model. These validated humanized dosage regimens and population pharmacokinetic models support translational studies with clinically relevant amikacin exposure profiles.

Improved characterization of aminoglycoside penetration into human lung epithelial lining fluid via population pharmacokinetics

Aminoglycosides are important treatment options for serious lung infections, but modeling analyses to quantify their human lung epithelial lining fluid (ELF) penetration are lacking. We estimated the extent and rate of penetration for five aminoglycosides via population pharmacokinetics from eight published studies. The area under the curve in ELF vs plasma ranged from 50% to 100% and equilibration half-lives from 0.61 to 5.80 h, indicating extensive system hysteresis. Aminoglycoside ELF peak concentrations were blunted, but overall exposures were moderately high.