Acute toxicity is a dose-limiting factor for intravenous polymyxin B: A safety and pharmacokinetic study in healthy Chinese subjects

Dodecapeptides derived from human cathelicidin with potent activity against carbapenem-resistant Acinetobacter baumannii

The increasing infections caused by carbapenem-resistant Acinetobacter baumannii (CRAB) poses a serious threat to global public health. Antimicrobial peptides (AMPs) are alternatives to conventional antibiotics in combating superbugs. However, discovering AMPs with low synthesis costs and strong antibacterial effects against CRAB is challenging. In this study, we synthesized 28 dodecapeptides for bactericidal assessment by site mutation and all-hydrocarbon stapling on the basis of the antibacterial core of human cathelicidin. The linear derivative d12 (Q5RD9I-KR12) and the i, i + 4 stapled peptide d24, which was generated by substituting Val4 and Lys8 of d12 to staples, stood out among the candidates. These short AMPs efficiently bound to bacterial membrane and penetrated it in a lipid A-dependent manner, resulting in low minimal inhibitory concentrations to inactivate CRAB clinical isolates (2.5-20 μg/mL). The CRAB infection mouse models of irradiation-assisted local pulmonary infection and intra-abdominal sepsis revealed that treatment with d12 and d24 significantly eliminated CRAB in vivo and thereby increased mouse survival. Owing to its improved proteolytic resistance, d24 outperformed d12 in suppressing intra-abdominal CRAB infection. The excellent antibacterial effects, good biocompatibility, and facile synthesis make d12 and d24 promising candidates to curb CRAB infections in different application scenarios.

A Systematic Review of Pharmacokinetic Studies of Colistin and Polymyxin B in Adult Populations

BACKGROUND AND OBJECTIVE

The pharmacokinetics of polymyxins are highly variable and conventional dosing regimens may likely lead to sub-optimal exposures and outcomes, particularly in critically ill patients with multi-drug-resistant infections. The aim of this systematic review is to describe the published pharmacokinetic data and to investigate variables that have been shown to affect the pharmacokinetics of colistimethate sodium, colistin, and polymyxin B in adult populations.

METHODS

Sixty studies were identified. A total of 27 and 33 studies described the pharmacokinetics of colistin and polymyxin B, respectively.

RESULTS

The most common dosing regimen for colistimethate sodium was a loading dose of 9 MIU, followed by 9 MIU/day in two to three divided doses, while for polymyxin B, a loading dose of 100-200 mg, followed by 50-100 mg every 12 h was given. Studies that used colistin sulfate instead of colistimethate sodium reported lower inter-individual variability, which may be attributed to the formulation of colistin sulfate being an active drug. The volume of distribution for colistin is typically lower in healthy individuals than in critically ill patients, owing to variations in physiological and pathological conditions. The clearance of colistimethate sodium in critically ill patients not undergoing dialysis was higher, around 13 L/h, compared with those receiving continuous renal replacement therapy, where clearance ranged from 2.31 to 8.23 L/h. In patients receiving continuous renal replacement therapy, clearance of colistin was higher compared with colistimethate sodium (2.06-6.63 L/h and 1.57-3.85 L/h, respectively). Colistin protein binding in critically ill patients ranged from 51% to 79%. The volume of distribution of polymyxin B was similar between critically ill and acutely ill patients, with range of 6.3-33.1 L and 6.22-38.6 L, respectively. Clearance of polymyxin B was also almost similar between critically ill and acutely ill patients (range of 1.27-2.32 L/h). There were two studies that reported free drug concentrations instead of the total drug concentrations of polymyxin B. In critically ill patients, protein binding ranged from 48.8% to 92.4% for polymyxin B. Creatinine clearance was the most common patient characteristic associated with altered clearance of colistimethate sodium and/or colistin, and polymyxin B.

CONCLUSIONS

Critically ill patients exhibit complex pharmacokinetics for colistin and polymyxin B, influenced by renal function, body weight, and clinical factors such as acute kidney injury, augmented renal clearance, serum albumin, and liver function. These factors necessitate individualized dosing adjustments to avoid toxicity and achieve therapeutic efficacy. Model-informed precision dosing provides a promising approach to optimize their use by integrating population pharmacokinetic parameters, patient-specific variables, and therapeutic drug monitoring, ensuring a balance between efficacy, safety, and resistance prevention.

Clinical outcomes and pharmacokinetics/pharmacodynamics of intravenous polymyxin B treatment for various site carbapenem-resistant gram-negative bacterial infections: a prospective observational multicenter study

Polymyxin B, a last resort for carbapenem-resistant gram-negative bacteria (CRGNB) infections, has infection site-specific pharmacokinetic/pharmacodynamic (PK/PD) properties. However, there is little clinical evidence to support optimal exposures of polymyxin B for different site infections. We performed a prospective, observational, multicenter study to evaluate the clinical outcomes and PK/PD of intravenous polymyxin B treatment for various site CRGNB infections. The main clinical outcomes were 14-day all-cause mortality and nephrotoxicity, and the secondary outcomes were 28-day mortality and clinical response. The area under curves (AUCs) of polymyxin B were determined, and their associations with clinical outcomes were analyzed by stratification based on the infection site. A total of 312 patients were ultimately enrolled from 10 research centers. The overall 14-day mortality was 29.5%, and those of patients with lower respiratory tract infection (LRTI), intra-abdominal infection (IAI), and bloodstream infection (BSI) were 32.3%, 19.7%, and 30.3%, respectively. The 28-day mortality rate was 38.1%, while LRTI patients had the highest mortality (41.4%) and IAI patients lowest (34.8%). The clinical response rate was 46.2%, which was similar among the subgroups. The overall AKI rate was 60.9%. An AUC greater than 50 mg∙h/L was related to lower mortality in IAI patients but not in LRTI patients, which led to a lower but not significant difference in the overall analysis. The AUC of polymyxin B was an independent risk factor for 14-day mortality in IAI patients, and the cutoff value was 76 mg∙h/L. The results would be helpful for personalized dosing and monitoring of polymyxin B.CLINICAL TRIALSThis study is registered with the Chinese Clinical Trial Registry as ChiCTR2200056667.

Colistin treatment causes neuronal loss and cognitive impairment via ros accumulation and neuronal plasticity alterations

The rise of antimicrobial resistance has made necessary the increase of the antibacterial arsenal against multidrug-resistant bacteria. In this context, colistin has re-emerged as a first-line antibiotic in critical situations despite its nephro- and neuro- toxicity at peripheral level. However, the mechanism underlying its toxicity remains unknown, particularly in relation to the central nervous system (CNS). Therefore, this study aimed to characterize the molecular mechanisms underlying colistin-induced neurotoxicity in the CNS through a combination of in vitro and in vivo molecular studies along with several in vivo behavioral tests. Following colistin treatment, mice exhibited a significant reduction in body weight together with renal impairment, and locomotor dysfunction. Moreover, our results demonstrated that colistin disrupted the blood-brain barrier, inducing astrogliosis, and triggering apoptosis-related processes probably through the accumulation of reactive oxygen species (ROS) and mitochondrial dysfunction. Further analysis on mice and primary neuronal cultures revealed that colistin administration altered neuronal plasticity by reducing the number of immature neurons in adult neurogenesis and altering the synaptic function through a reduction of the post-synaptic protein PSD95. All these alterations together finally lead to cognitive impairment and depression-like symptoms in mice. These findings provide novel insights into the mechanisms of colistin-induced neurotoxicity in the CNS, highlighting the need for careful monitoring of cognitive function in patients undergoing colistin treatment.

Phase 1 study of the safety, tolerability, and pharmacokinetics of a synthetic macrocyclic peptide antibiotic (BRII-693) in healthy adult participants

BRII-693 is a next-generation intravenous (IV)-administered synthetic macrocyclic peptide antibiotic for infections caused by drug-resistant gram-negative pathogens. This single-center, randomized, double-blind, placebo-controlled phase 1 study investigated the safety, tolerability, and pharmacokinetics (PK) of single and multiple ascending doses of BRII-693 in 104 healthy participants. In single-dose cohorts, 10-400 mg of BRII-693 was evaluated in eight participants (six active; two placebo) per cohort. In the 7-day repeat-dose cohorts, 100-200 mg of BRII-693 was evaluated in eight participants (six active; two placebo) per cohort. In two 14-day repeat-dose cohorts, 150 mg of BRII-693 was evaluated in 12 participants (10 active, two placebo) each of non-Chinese and Chinese descent. No participant reported a severe or serious adverse event (AE) or an AE leading to death. Across all cohorts and for non-Chinese and Chinese participants, most AEs were mild. Cmax and area under the concentration-time curve (AUC) increased in a dose-proportional manner over the dose range of single- and repeat-dosing. Mean t1/2 was 2.58-4.37 hours and generally similar across single doses. An accumulation of exposure was observed following multiple doses with an accumulation ratio of 1.5 to 1.7 which was within the expected 1.3 to 2.5 range at steady state. Mean total clearance (CL) was similar between single and multiple dose administration, suggesting time-independent pharmacokinetics (PK). PK exposure was statistically equivalent between non-Chinese and Chinese participants. This phase 1 study demonstrates a favorable safety, tolerability, and PK profile of BRII-693 in healthy non-Chinese and Chinese participants.CLINICAL TRIALSThis study is registered with ClinicalTrials.gov as NCT04808414.

Design, synthesis, and bioactivity investigation of novel cyclic lipopeptide antibiotics targeting top-priority multidrug-resistant gram-negative bacteria

OBJECTIVES

Polymyxins are the last-line therapy for top-priority multidrug-resistant (MDR) gram-negative bacteria. However, polymyxin nephrotoxicity impedes its clinical application. This study aimed to design, synthesize, and identify a novel and promising polymyxin derivative with high efficacy and low toxicity.

METHODS

To design polymyxin derivatives, we reduced the hydrophobicity of the two hydrophobic domains (fatty acyl chain and D-Phe6-L-Leu7) and modified the positive charged L-2,4-diaminobutyric acid (Dab) residues. Twenty-five derivatives were synthesized, and their antibacterial activities in vitro and renal cytotoxicities were determined. The nephrotoxicity and pharmacokinetic parameters of compound 12 were examined in rats. Antibacterial efficacy in vivo was evaluated using a mouse systemic infection model. Surface plasmon resonance analysis, compound 12-rifampicin combination therapy, and scanning electron microscopy were used to study the mechanism of action of compound 12.

RESULTS

This research found a new compound, identified as compound 12, which showed similar or increased antibacterial activity against all tested sensitive and carbapenem-resistant gram-negative bacteria. It exhibited reduced renal cytotoxicity and nephrotoxicity, a favorable pharmacokinetic profile, and maintained or improved antibacterial efficacy in vivo. Importantly, its anti-Pseudomonas aeruginosa activity significantly improved. Compound 12, when combined with rifampicin, enhanced the activity of rifampin against gram-negative bacteria. Compound 12 also showed a high affinity for lipopolysaccharide and disrupted cell membrane integrity.

CONCLUSION

Reducing the hydrophobicity of the two domains reduced renal cytotoxicity and nephrotoxicity. Shortening the side chain of Dab3 by one carbon maintained or increased its antibacterial activity both in vitro and in vivo. Furthermore, only the length of the side chain of Dab9 could be shortened by one carbon among the Dab1,5 and Dab8,9 residues. The bactericidal effects of compound 12 were related to the disruption of cell membrane integrity. Compound 12 may be a promising candidate for combating sensitive and carbapenem-resistant gram-negative bacterial infections, especially Pseudomonas aeruginosa.

Pharmacokinetic study of polymyxin B in healthy subjects and subjects with renal insufficiency

Polymyxin B is a viable option for treating antibiotic-resistant infections; however, current data on its pharmacokinetics, particularly in patients with renal insufficiency, remain inconclusive and necessitates further investigation. To address this gap, we conducted an open-label, single-center, single-dose, parallel-group pharmacokinetic study. Participants received an intravenous dose of 0.75 mg/kg of polymyxin B and were categorized based on their renal function: those with normal function (creatinine clearance [CLcr] ≥ 90 mL/min), mild renal insufficiency (CLcr 60-89 mL/min), and end-stage kidney disease patients on intermittent hemodialysis (IHD) (CLcr < 10 mL/min). The pharmacokinetic parameters assessed included the area under the curve (AUC), maximum concentration (Cmax), clearance rate (CL), volume of distribution (Vz), and half-life (t1/2). Results indicated that subjects with mild renal insufficiency exhibited pharmacokinetic profiles similar to healthy individuals. Nevertheless, in patients undergoing long-term IHD, we observed significant differences: the AUC was 58% higher, Cmax was 29% lower, CL was 42% lower, Vz was 60% larger, and t1/2 was extended by 10 h compared to healthy controls. Secondary outcomes revealed good tolerability of polymyxin B across all groups, with no serious adverse effects related to renal function. In summary, while kidney function may have a slight impact on the pharmacokinetic of polymyxin B, it does not compromise the drug's therapeutic effectiveness.

Thanatin and vinyl sulfide analogues as narrow spectrum antimicrobial peptides that synergise with polymyxin B

Thanatin is a β-hairpin antimicrobial peptide cyclised by a single disulfide bond that has shown potent broad-spectrum activity towards bacterial and fungal pathogens. Towards Gram-negative species, thanatin acts both by forming trans-membranal pores and inhibiting outer membrane biogenesis by binding to LptA and blocking lipopolysaccharide (LPS) transport. Inspired by previous modifications of thanatin, an analogue was prepared which demonstrated potent but selective activity towards E. coli. Furthermore, this compound was shown to act in synergy with the highly potent FDA-approved lipopeptide antibiotic polymyxin B, which engages LPS at the cytoplasmic membrane. Four analogues of thanatin in which the disulfide was substituted for vinyl sulfide bridge mimetics were prepared, all of which retained similar secondary structures. Two of these retained substantial potency and selectivity towards E. coli. Importantly, synergy with polymyxin B was also maintained for the lead analogue. The vinyl sulfide potentially offers a facile replacement strategy for labile disulfide bonds and the selective activity and drug synergy of the reported thanatin analogues is promising for the development of narrow spectrum antimicrobials with reduced likelihood of resistance emerging in clinical settings.

Pharmacokinetics and safety of colistin sulfate after single and multiple intravenous doses in healthy Chinese subjects

OBJECTIVE

Increasing antimicrobial resistance has led to the revival of the polymyxins as a last-resort therapeutic option for multidrug-resistant Gram-negative bacterial infections. A parenteral formulation of colistin sulfate is available solely in China. While the onset of action of IV colistin may occur faster than with its prodrug CMS, its pharmacokinetic (PK) profile remains unclear.

METHODS

This single-centre, open-label, single- and multi-dose, phase 1 trial examined the PKs and safety of colistin sulfate in healthy Chinese adults. Participants received a single 10,000 units/kg (equivalent to 0.452 mg/kg) dose of colistin sulfate (single-dose group, n = 12) or the same dose q12h for 7 days (multi-dose group, n = 12) via a 2-h IV infusion. Colistin concentrations in plasma and urine were determined using LC-MS/MS, and the PK parameters calculated using non-compartmental analysis.

RESULTS

After a single dose the peak concentration (Cmax), area under the curve from 0 to 12 h (AUC0-12h), terminal half-life (T1/2), volume of distribution (Vd), and total body clearance (CL) of colistin were 1.08 ± 0.18 mg/L, 4.73 ± 0.89 h·mg/L, 3.65 ± 0.55 h, 16.82 ± 2.70 L, and 3.24 ± 0.51 L/h, respectively. No accumulation of colistin was observed after multiple doses. The cumulative urinary recovery of colistin was 0.9 ± 0.7% within 24 h after multi-dose administration. No nephrotoxicity was reported.

CONCLUSIONS

This study is the first to report colistin PKs in healthy Chinese subjects after single and multiple doses of colistin sulfate. The PK and safety data are required for optimal dose selection in clinical practice.

Evaluating nephrotoxicity reduction in a novel polymyxin B formulation: insights from a 3D kidney-on-a-chip model

This study aimed to assess the nephrotoxicity associated with VRP-034 (novel formulation of polymyxin B [PMB]) compared to marketed PMB in a three-dimensional (3D) kidney-on-a-chip model. To model the human kidney proximal tubule for analysis, tubular structures were established using 23 triple-channel chips seeded with RPTEC/hTERT1 cells. These cells were exposed to VRP-034 or PMB at seven concentrations (1-200 µM) over 12, 24, and 48 h. A suite of novel kidney injury biomarkers, cell health, and inflammatory markers were quantitatively assessed in the effluent. Additionally, caspase and cytochrome C levels were measured, and cell viability was evaluated using calcein AM and ethidium homodimer-1 (EthD-1). Exposure to marketed PMB resulted in significantly elevated levels (P < 0.05) of four key biomarkers (KIM-1, cystatin C, clusterin, and OPN) compared to VRP-034, particularly at clinically relevant concentrations of ≥10 µM. At 25 µM, all biomarkers demonstrated a significant increase (P < 0.05) with marketed PMB exposure compared to VRP-034. Inflammatory markers (interleukin-6 and interleukin-8) increased significantly (P < 0.05) with marketed PMB at concentrations of ≥5 µM, relative to VRP-034. VRP-034 displayed superior cell health outcomes, exhibiting lower lactate dehydrogenase release, while ATP levels remained comparable. Morphological analysis revealed that marketed PMB induced more severe damage, disrupting tubular integrity. Both treatments activated cytochrome C, caspase-3, caspase-8, caspase-9, and caspase-12 in a concentration-dependent manner; however, caspase activation was significantly reduced (P < 0.05) with VRP-034. This study demonstrates that VRP-034 significantly reduces nephrotoxicity compared to marketed PMB within a 3D microphysiological system, suggesting its potential to enable the use of full therapeutic doses of PMB with an improved safety profile, addressing the need for less nephrotoxic polymyxin antibiotics.

Outcome of intravenous and inhaled polymyxin B treatment in patients with multidrug-resistant gram-negative bacterial pneumonia

PURPOSE

The incidence of pneumonia caused by multidrug-resistant gram-negative bacteria (MDR GNB) is increasing, which imposes significant burden on public health. Inhalation combined with intravenous polymyxins has emerged as a viable treatment option. However, pharmacokinetic studies focusing on intravenous and inhaled polymyxin B (PMB) are limited.

METHODS

This study included seven patients with MDR GNB-induced pneumonia who were treated with intravenous plus inhaled PMB from March 1 to November 30, 2022, in the intensive care unit of the First Affiliated Hospital of Zhejiang University School of Medicine. Clinical outcomes and therapeutic drug monitoring data of PMB in both plasma and epithelial lining fluid (ELF) were retrospectively reviewed.

RESULTS

Median PMB concentrations in the ELF were 7.83 (0.72-66.5), 116.72 (17.37-571.26), 41.1 (3.69-133.78) and 33.82 (0.83-126.68) mg/L at 0, 2, 6 and 12 h, respectively, and were much higher than those detected in the serum. ELF concentrations of PMB at 0, 2, 6 and 12 h were higher than the minimum inhibitory concentrations of pathogens isolated from the patients. Steady-state concentrations of PMB in the plasma were >2 mg/L in most patients. Of the patients, 57.14% were cured and 71.43% showed a favourable microbiological response. The incidence of side effects with PMB was low.

CONCLUSIONS

Inhaled plus intravenous PMB can achieve high ELF concentrations and favourable clinical outcomes without an increased adverse effect profile. This treatment approach appears promising for the treatment of patients with pneumonia caused by MDR-GNB.

Transmission Dynamics and Novel Treatments of High Risk Carbapenem-Resistant Klebsiella pneumoniae: The Lens of One Health

The rise of antibiotic resistance and the dwindling antimicrobial pipeline have emerged as significant threats to public health. The emergence of carbapenem-resistant Klebsiella pneumoniae (CRKP) poses a global threat, with limited options available for targeted therapy. The CRKP has experienced various changes and discoveries in recent years regarding its frequency, transmission traits, and mechanisms of resistance. In this comprehensive review, we present an in-depth analysis of the global epidemiology of K. pneumoniae, elucidate resistance mechanisms underlying its spread, explore evolutionary dynamics concerning carbapenem-resistant hypervirulent strains as well as KL64 strains of K. pneumoniae, and discuss recent therapeutic advancements and effective control strategies while providing insights into future directions. By going through up-to-date reports, we found that the ST11 KL64 CRKP subclone with high risk demonstrated significant potential for expansion and survival benefits, likely due to genetic influences. In addition, it should be noted that phage and nanoparticle treatments still pose significant risks for resistance development; hence, innovative infection prevention and control initiatives rooted in One Health principles are advocated as effective measures against K. pneumoniae transmission. In the future, further imperative research is warranted to comprehend bacterial resistance mechanisms by focusing particularly on microbiome studies' application and implementation of the One Health strategy.

Three methods to optimise polymyxin B dosing using estimated AUC after first dose: validation with the data generated by Monte Carlo simulation

To achieve the AUC-guided dosing, we proposed three methods to estimate polymyxin B AUC across 24 h at steady state (AUCSS,24h) using limited concentrations after its first dose.Monte Carlo simulation based on a well-established population PK model was performed to generate the PK profiles of 1000 patients with normal or abnormal renal function. Polymyxin B AUCSS,24h was estimated for each subject using three methods (two-point PK approach, three-point PK approach, and four-point PK approach) based on limited concentration data in its first dose and compared with the actual AUC at steady state calculated using the linear-trapezoidal formula.In patients with normal renal function, the mean bias of two-point PK approach, three-point PK approach, and four-point PK approach was -8.73%, 1.37%, and -0.48%, respectively. The corresponding value was -11.15%, 1.99%, and -0.28% in patients with renal impairment, respectively. The largest mean bias of two-point PK approach, three-point PK approach, and four-point PK approach was -12.63%, -6.47%, and -0.54% when the sampling time shifted.The Excel calculators designed based on the three methods can be potentially used to optimise the dosing regimen of polymyxin B in the clinic.

Factors affecting the effectiveness and safety of polymyxin B in the treatment of Gram-negative bacterial infections: A meta-analysis of 96 articles

PURPOSE

Polymyxin B, with its unique structure and mechanism of action, has emerged as a key therapeutic agent against Gram-negative bacteria. The study aims to explore potential factors to influence its effectiveness and safety.

METHODS

A model-based meta-analysis of 96 articles was conducted, focusing on factors like dosage, bacterial species, and combined antibiotic therapy. The analysis evaluated mortality rates and incidence rate of renal dysfunction, also employing parametric survival models to assess 30-d survival rates.

RESULTS

In the study involving 96 articles and 9716 patients, polymyxin B's daily dose showed minimal effect on overall mortality, with high-dose group mortality at 33.57% (95% confidence intervals [CI]: 29.15-38.00) compared to the low-dose group at 35.44% (95% CI: 28.99-41.88), P = 0.64. Mortality significantly varied by bacterial species, with Pseudomonas aeruginosa infections at 58.50% (95% CI: 55.42-63.58). Monotherapy exhibited the highest mortality at 40.25% (95% CI: 34.75-45.76), P < 0.01. Renal dysfunction was more common in high-dose patients at 29.75% (95% CI: 28.52-30.98), with no significant difference across antibiotic regimens, P = 0.54. The 30-d overall survival rate for monotherapy therapy was 63.6% (95% CI: 59.3-67.5) and 70.2% (95% CI: 64.4-76.2) for association therapy with β-lactam drugs.

CONCLUSIONS

The dosage of polymyxin B does not significantly change death rates, but its effectiveness varies based on the bacterial infection. Certain bacteria like P. aeruginosa are associated with higher mortality. Combining polymyxin B with other antibiotics, especially β-lactam drugs, improves survival rates. Side effects depend on the dose, with lower doses being safer. These findings emphasize the importance of customizing treatment to balance effectiveness and safety.

Polymyxin B vs. colistin: the comparison of neurotoxic and nephrotoxic effects of the two polymyxins

BACKGROUND

The study aimed to compare polymyxin B with colistimethate sodium (CMS) regarding neurotoxicity, nephrotoxicity and 30-day mortality in patients with MDR Gram-negatives.

METHODS

All adult patients who received polymyxin B or CMS for at least 24 h for the treatment of MDR microorganisms were evaluated retrospectively.

RESULTS

Among 413 initially screened patients, 147 patients who were conscious and able to express their symptoms were included in the neurotoxicity analysis. 13 of 77 patients with polymyxin B and 1 of 70 with CMS had neurotoxic adverse events, mainly paresthesias. All events were reversible after drug discontinuation. Among 290 patients included in nephrotoxicity analysis, the incidence of acute kidney injury (AKI) was 44.7% and 40.0% for polymyxin B and CMS, respectively (p = 0.425). AKI occurred two days earlier with colistin than polymyxin B without statistical significance (median (IQR): 5 (3-11) vs. 7 (3-12), respectively, p = 0.701). Polymyxin therapy was withdrawn in 41.1% of patients after AKI occurred and CMS was more frequently withdrawn than polymyxin B (p = 0.025). AKI was reversible in 91.6% of patients with CMS and 79% with polymyxin B after the drug withdrawal. Older age, higher baseline serum creatinine and the use of at least two nephrotoxic drugs were independent factors associated with AKI (OR 1.05, p < 0.001; OR 2.99, p = 0.022 and OR 2.45, p = 0.006, respectively). Septic shock, mechanical ventilation, presence of a central venous catheter and Charlson comorbidity index (OR 2.13, p = 0.004; OR 3.37, p < 0.001; OR 2.47, p = 0.004 and OR 1.21, p p < 0.001, respectively) were the independent predictors of mortality. The type of polymyxin was not related to mortality.

CONCLUSIONS

Neurotoxicity is a relatively common adverse event that leads to drug withdrawal during polymyxins, particularly polymyxin B. Nephrotoxicity is very common during polymyxin therapy and the two polymyxins display similar nephrotoxic events with high reversibility rates after drug withdrawal. Close monitoring of AKI is crucial during polymyxin therapy, particularly, for elderly patients, patients who have high baseline creatinine, and using other nephrotoxic drugs.

A simple HPLC-MS/MS method for the determination of polymyxin B in human plasma and its application in the pharmacokinetic study in elderly patients infected with multidrug-resistant Gram-negative bacteria

Introduction: Polymyxin B is widely used to treat infections caused by multidrug-resistant Gram-negative bacteria. However, the pharmacokinetic study data of PB in the elderly are scarce. Herein, a simple method to measure the concentration of PB in human plasma was developed and validated by high performance liquid chromatography-tandem mass spectrometry, and it was applied to a PK study in the elderly. Methods: PB was extracted from human plasma by a rapid protein-precipitation method using 0.1% formic acid in methanol and then separated on an ultimate AQ-C18 column using linear gradient elution with a 0.5-mL/min flow rate. Subsequently, PB was detected using a mass spectrometer operated in positive-ion and multiple-reaction-monitoring modes. Results: The lower limits of quantification of the method for Polymyxin B1 and Polymyxin B2 were 1.00 and 0.10 μg/mL, respectively. The linear ranges for PB1 and PB2 were 1.00-20.02 and 0.10-2.04 μg/mL, respectively. Patients receiving a 75-mg maintenance dose every 12h had AUCss, 24 h, and Css, av values of 117.70 ± 37.03 μg h/mL and 4.14 ± 1.74 μg/mL, respectively. For patients receiving a 100 mg maintenance dose, these values were 152.73 ± 70.09 μg h/mL and 5.43 ± 2.85 μg/mL, respectively. Conclusion: The validated HPLC-MS/MS method was successfully applied to a study on the pharmacokinetics of PB in elderly patients infected with multidrug-resistant Gram-negative bacteria. Both two dose strategies in this study would have a excessive PB exposure in the elderly patients then the therapeutic window recommended by guidelines.

Recent Advances in the Development of Polymyxin Antibiotics: 2010-2023

The polymyxins are nonribosomal lipopeptides produced by Paenibacillus polymyxa and are potent antibiotics with activity specifically directed against Gram-negative bacteria. While the clinical use of polymyxins has historically been limited due to their toxicity, their use is on the rise given the lack of alternative treatment options for infections due to multidrug resistant Gram-negative pathogens. The Gram-negative specificity of the polymyxins is due to their ability to target lipid A, the membrane embedded LPS anchor that decorates the cell surface of Gram-negative bacteria. Notably, the mechanisms responsible for polymyxin toxicity, and in particular their nephrotoxicity, are only partially understood with most insights coming from studies carried out in the past decade. In parallel, many synthetic and semisynthetic polymyxin analogues have been developed in recent years in an attempt to mitigate the nephrotoxicity of the natural products. Despite these efforts, to date, no polymyxin analogues have gained clinical approval. This may soon change, however, as at the moment there are three novel polymyxin analogues in clinical trials. In this context, this review provides an update of the most recent insights with regard to the structure-activity relationships and nephrotoxicity of new polymyxin variants reported since 2010. We also discuss advances in the synthetic methods used to generate new polymyxin analogues, both via total synthesis and semisynthesis.

Molecular Weights of Polyethyleneimine-Dependent Physicochemical Tuning of Gold Nanoparticles and FRET-Based Turn-On Sensing of Polymyxin B

Environmental monitoring and the detection of antibiotic contaminants require expensive and time-consuming techniques. To overcome these challenges, gold nanoparticle-mediated fluorometric "turn-on" detection of Polymyxin B (PMB) in an aqueous medium was undertaken. The molecular weight of polyethyleneimine (PEI)-dependent physicochemical tuning of gold nanoparticles (PEI@AuNPs) was achieved and employed for the same. The three variable molecular weights of branched polyethyleneimine (MW 750, 60, and 1.3 kDa) molecules controlled the nano-geometry of the gold nanoparticles along with enhanced stabilization at room temperature. The synthesized gold nanoparticles were characterized through various advanced techniques. The results revealed that polyethyleneimine-stabilized gold nanoparticles (PEI@AuNP-1-3) were 4.5, 7.0, and 52.5 nm in size with spherical shapes, and the zeta potential values were 29.9, 22.5, and 16.6 mV, respectively. Accordingly, the PEI@AuNPs probes demonstrated high sensitivity and selectivity, with a linear relationship curve over a concentration range of 1-6 μM for polymyxin B. The limit of detection (LOD) was calculated as 8.5 nM. This is the first unique report of gold nanoparticle nano-geometry-dependent FRET-based turn-on detection of PMB in an aqueous medium. We believe that this approach would offer a complementary strategy for the development of a highly sophisticated and advanced sensing system for PMB and act as a template for the development of new nanomaterial-based engineered sensors for rapid antibiotic detection in environmental as well as biological samples.

Antimicrobial resistance crisis: could artificial intelligence be the solution?

Antimicrobial resistance is a global public health threat, and the World Health Organization (WHO) has announced a priority list of the most threatening pathogens against which novel antibiotics need to be developed. The discovery and introduction of novel antibiotics are time-consuming and expensive. According to WHO's report of antibacterial agents in clinical development, only 18 novel antibiotics have been approved since 2014. Therefore, novel antibiotics are critically needed. Artificial intelligence (AI) has been rapidly applied to drug development since its recent technical breakthrough and has dramatically improved the efficiency of the discovery of novel antibiotics. Here, we first summarized recently marketed novel antibiotics, and antibiotic candidates in clinical development. In addition, we systematically reviewed the involvement of AI in antibacterial drug development and utilization, including small molecules, antimicrobial peptides, phage therapy, essential oils, as well as resistance mechanism prediction, and antibiotic stewardship.

Acute kidney injury associated with colistin sulfate vs. polymyxin B sulfate therapy: A real-world, retrospective cohort study

OBJECTIVE

To compare the incidence of acute kidney injury (AKI) in patients treated with colistin sulfate (CS) and polymyxin B sulfate (PMB).

METHODS

Sociodemographic and laboratory measures of adult patients who received intravenous CS or PMB for at least 72 h for the first time at the study hospital from October 2021 to November 2022 were collected retrospectively. The primary outcome was the incidence of AKI, defined by the Kidney Diseases Improving Global Outcomes criteria. The secondary outcome was 30-day mortality.

RESULTS

In total, 109 patients were included in the CS cohort and 176 patients were included in the PMB cohort. The incidence of AKI was significantly higher in the PMB cohort compared with the CS cohort (50.6% vs. 18.3%; P<0.001). On multi-variate analysis, CS therapy [hazard ratio (HR) 0.275; P<0.001] was an independent protective factor for AKI, along with higher estimated glomerular filtration rate. Nevertheless, 30-day mortality was similar in the PMB and CS cohorts (21.6% vs. 13.8%; P=0.099). Multi-variate analyses revealed that CS therapy was not associated with 30-day mortality (HR 0.968; P=0.926), while intensive care unit admission, combination with meropenem, Charlson score and stage 3 AKI were independent risk factors for 30-day mortality. After balancing the baseline characteristics of patients using propensity score matching, the main results were unchanged.

CONCLUSION

The incidence of AKI was significantly lower in the CS cohort compared with the PMB cohort. However, 30-day mortality was similar in the two cohorts.

Polymyxin B-related neurotoxicity: a brief case report

Polymyxin B and colistin are considered the last therapeutic option to treat infections caused by highly drug-resistant bacteria. However, their administration may lead to various adverse effects such as nephrotoxicity, neurotoxicity, and allergic reactions. The current case report presents the clinical manifestation of polymyxin B-associated neurotoxicity in a female patient with no chronic illness history. The patient was rescued from under rubble during an earthquake. She was diagnosed with an intra-abdominal infection caused by Acinetobacter baumannii (A. baumannii) After the initiation of the polymyxin B infusion, the patient developed numbness and tingling sensations in her hands, face, and head. On discontinuing polymyxin B and starting colistimethate, the patient's symptoms improved. Therefore, healthcare professionals should be aware of the potential risk factors associated with neurotoxicity in patients receiving polymyxin B. On identifying such symptoms treatment should be discontinued promptly to prevent further neurological damage.

Semisynthetic polymyxins with potent antibacterial activity and reduced kidney cell toxicity

The growing incidence of infections caused by multi-drug resistant Gram-negative bacteria has led to an increased use of last-resort antibiotics such as the polymyxins. Polymyxin therapy is limited by toxicity concerns, most notably nephrotoxicity. Recently we reported the development of a novel class of semisynthetic polymyxins with reduced toxicity wherein the N-terminal lipid and diaminobutyric acid residue are replaced by a cysteine-linked lipid featuring a reductively labile disulfide bond. In the present study we further explored the potential of this approach by also varying the amino acid residue directly adjacent to the polymyxin macrocycle. This led to the identification of new semisynthetic polymyxins that maintain the potent antibacterial activity of the clinically used polymyxin B while exhibiting a further reduction in toxicity toward human proximal tubule epithelial cells. Furthermore, these new polymyxins were found to effectively synergize with novobiocin, rifampicin, and erythromycin against mcr-positive, polymyxin resistant E. coli.

Polymyxin B inhibits pro-inflammatory effects of E. coli outer membrane vesicles whilst increasing immune cell uptake and clearance

Polymyxin B (PMB) is a peptide based antibiotic that binds the lipid A moiety of lipopolysaccharide (LPS) with a resultant bactericidal effect. The interaction of PMB with LPS presented on outer membrane vesicles (OMVs) is not fully known, however, a sacrificial role of OMVs in protecting bacterial cells by sequestering PMB has been described. Here we assess the ability of PMB to neutralize the immune-stimulatory properties of OMVs whilst modulating the uptake of OMVs in human immune cells. We show for the first time that PMB increases immune cell uptake of Escherichia coli derived OMVs whilst inhibiting TNF and IL-1β production. Therefore, we present a potential new role for PMB in the neutralization of OMVs via LPS masking and increased immune cell uptake.

Population pharmacokinetic analysis and dosing optimization of polymyxin B in critically ill patients

Objectives: Since the global broadcast of multidrug-resistant gram-negative bacteria is accelerating, the use of Polymyxin B is sharply increasing, especially in critically ill patients. Unsatisfactory therapeutic effects were obtained because of the abnormal physiological function in critically ill patients. Therefore, the determination of optimal polymyxin B dosage becomes highly urgent. This study aimed to illustrate the polymyxin B pharmacokinetic characteristics by defining the influencing factors and optimizing the dosing regimens to achieve clinical effectiveness.

Methods: Steady-state concentrations of polymyxin B from twenty-two critically ill patients were detected by a verified liquid chromatography-tandem mass spectrometry approach. The information on age, weight, serum creatinine, albumin levels, and Acute Physiology and Chronic Health Evaluation-II (APACHE-II) score was also collected. The population PK parameters were calculated by the non-parametric adaptive grid method in Pmetrics software, and the pharmacokinetic/pharmacodynamics target attainment rate was determined by the Monte Carlo simulation method.

Results: The central clearance and apparent volume of distribution for polymyxin B were lower in critically ill patients (1.24 ± 0.38 L h-1 and 16.64 ± 12.74 L, respectively). Moreover, albumin (ALB) levels can be used to explain the variability in clearance, and age can be used to describe the variability in the apparent volume of distribution. For maintaining clinical effectiveness and lowering toxicity, 75 mg q12 h is the recommended dosing regimen for most patients suffering from severe infections.

Conclusion: This study has clearly defined that in critically ill patients, age and ALB levels are potentially important factors for the PK parameters of polymyxin B. Since older critically ill patients tend to have lower ALB levels, so higher dosages of polymyxin B are necessary for efficacy.

Ratiometric detection of polymyxin B based on the disaggregation of pyrenyl nanoassemblies in 100% aqueous media

Polymyxin B (PMB) was an antibiotic with highly effective antibacterial effect but narrow safety interval, and its residues in food had attracted widespread attention. It was important to develop an accurate method for the rapid detection of PMB in animal foods. In this work, we had established a ratiometric sensing system based on the formation of supramolecular assemblies of pyrenyl probes, which were driven by the synergy of noncovalent forces such as multiple-electrostatic and π-π stacking interactions. Compared with the traditional fluorescence detection based on the single wavelength change, the present approach showing two-wavelength fluorescence response could reduce the interference of other factors making the experimental results more accurate. The sensor exhibited high sensitivity and selectivity with a low detection limit (28.3 nM). This method could be used to realize visual detection and had a visual detection limit of 1 μM. As we had learned yet, this was the first ratiometric sensor for PMB detection in aqueous solution. We believed all our preliminary would not only provide a complementary strategy for the detection of PMB, but also develop some new ideas for the construction of sensors for rapid antibiotic detection.

Pharmacokinetics/pharmacodynamics of polymyxin B in patients with bloodstream infection caused by carbapenem-resistant Klebsiella pneumoniae

Introduction: Polymyxin B is a last-line therapy for carbapenem-resistant microorganisms. However, a lack of clinical pharmacokinetic/pharmacodynamic (PK/PD) data has substantially hindered dose optimization and breakpoint setting. Methods: A prospective, multi-center clinical trial was undertaken with polymyxin B [2.5 mg/kg loading dose (3-h infusion), 1.25 mg/kg/12 h maintenance dose (2-h infusion)] for treatment of carbapenem-resistant K. pneumoniae (CRKP) bloodstream infections (BSI). Safety, clinical and microbiological efficacy were evaluated. A validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was applied to determine the concentrations of polymyxin B in blood samples. Population pharmacokinetic (PK) modeling and Monte Carlo simulations were conducted to examine the susceptibility breakpoint for polymyxin B against BSI caused by CRKP. Results: Nine patients were enrolled and evaluated for safety. Neurotoxicity (5/9), nephrotoxicity (5/9), and hyperpigmentation (1/9) were recorded. Blood cultures were negative within 3 days of commencing therapy in all 8 patients evaluated for microbiological efficacy, and clinical cure or improvement occurred in 6 of 8 patients. C_max and C_min following the loading dose were 5.53 ± 1.80 and 1.62 ± 0.41 mg/L, respectively. With maintenance dosing, AUC_ss,24 h was 79.6 ± 25.0 mg h/L and C_ss,avg 3.35 ± 1.06 mg/L. Monte Carlo simulations indicated that a 1 mg/kg/12-hourly maintenance dose could achieve >90% probability of target attainment (PTA) for isolates with minimum inhibitory concentration (MIC) ≤1 mg/L. PTA dropped substantially for MICs ≥2 mg/L, even with a maximally recommended daily dose of 1.5 mg/kg/12-hourly. Conclusion: This is the first clinical PK/PD study evaluating polymyxin B for BSI. These results will assist to optimize polymyxin B therapy and establish its breakpoints for CRKP BSI.

Carbapenem-resistant Acinetobacter baumannii: A challenge in the intensive care unit

Carbapenem-resistant Acinetobacter baumannii (CRAB) has become one of the leading causes of healthcare-associated infections globally, particularly in intensive care units (ICUs). Cross-transmission of microorganisms between patients and the hospital environment may play a crucial role in ICU-acquired CRAB colonization and infection. The control and treatment of CRAB infection in ICUs have been recognized as a global challenge because of its multiple-drug resistance. The main concern is that CRAB infections can be disastrous for ICU patients if currently existing limited therapeutic alternatives fail in the future. Therefore, the colonization, infection, transmission, and resistance mechanisms of CRAB in ICUs need to be systematically studied. To provide a basis for prevention and control countermeasures for CRAB infection in ICUs, we present an overview of research on CRAB in ICUs, summarize clinical infections and environmental reservoirs, discuss the drug resistance mechanism and homology of CRAB in ICUs, and evaluate contemporary treatment and control strategies.

Does Monitoring Total and Free Polymyxin B1 Plasma Concentrations Predict Polymyxin B-Induced Nephrotoxicity? A Retrospective Study in Critically Ill Patients

INTRODUCTION

The correlation between total and free polymyxin B (PMB including PMB1 and PMB2) exposure in vivo and acute kidney injury (AKI) remains obscure. This study explores the relationships between plasma exposure of PMB1 and PMB2 and nephrotoxicity, and investigates the risk factors for PMB-induced acute kidney injury (AKI) in critically ill patients.

METHODS

Critically ill patients who used PMB and met the criteria were enrolled. The total plasma concentration and plasma binding of PMB1 and PMB2 were analysed by liquid chromatography-tandem mass spectrometry and equilibrium dialysis.

RESULTS

A total of 89 patients were finally included, and AKI developed in 28.1% of them. The peak concentration of PMB1 (C_max (B1)) (adjusted odds ratio (AOR) = 1.68, 95% CI 1.08-2.62, p = 0.023), baseline BUN level (AOR = 1.08, 95% CI 1.01-1.16, p = 0.039) and hypertension (AOR = 3.73, 95% CI 1.21-11.54, p = 0.022) were independent risk factors for PMB-induced AKI. The area under the ROC curve of the model was 0.799. When C_max (B1) was 5.23 μg/ml or more, the probability of AKI was higher than 50%. The ratio of PMB1/PMB2 decreased after PMB preparation entered into the body. The protein binding rate in critically ill patients indicated significant individual differences. Free C_max (B) and free C_max (B1) levels in the AKI group were significantly (p < 0.05) higher than those in the non-AKI group. Total and free concentrations of PMB in patients showed a positive correlation.

CONCLUSIONS

Both the ROC curve and logistic regression model showed that C_max (B1) was a good predictor for the probability of PMB-induced AKI. Early therapeutic drug monitoring (TDM) of PMB should be considered in critically ill patients. Compared with C_min (B), C_max (B) and C_max (B1) may be helpful for the early prediction of PMB-induced AKI in critically ill patients.

Higher Incidence of Neurotoxicity and Skin Hyperpigmentation in Renal Transplant Patients Treated With Polymyxin B

BACKGROUND

Toxicity is a major concern related to the clinical use of polymyxin B, and available safety data for renal transplant patients are limited.

AIMS

We investigated the safety of polymyxin B and toxicity risk factors in renal transplant patients.

METHODS

A prospective study was performed on a group of renal transplant patients who received intravenous polymyxin B between January 2018 and August 2021. Polymyxin B treatment was monitored to evaluate toxicity and risk factors.

RESULTS

A total of 235 courses of polymyxin B were administered to 213 patients. Of these, 121 (51.5%) developed SH, 149 (63.4%) developed neurotoxicity, and 10 (5.5%) developed acute kidney injury of which 80% was reversible. Risk factors for developing SH included a high total dose by weight (OR=1.31, 95%CI: 1.08-1.60, p=0.008) and the presence of neurotoxicity (OR=2.86, 95%CI: 1.56-5.26, p=0.001). Neurotoxicity manifested during the first two days of treatment. Neurotoxicity occurred most commonly in women (OR=3.84, 95%CI: 1.82-8.10, p<0.0001), and the presence of SH (OR=1.98, 95%CI: 1.13-3.46, p=0.016) was also an independent risk factor.

CONCLUSIONS

Neurotoxicity and SH are the two major adverse effects of polymyxin B in renal transplant patients, which may limit its clinical use.

Pharmacokinetics and pharmacodynamics of peptide antibiotics

Antimicrobial resistance is a major global health challenge. As few new efficacious antibiotics will become available in the near future, peptide antibiotics continue to be major therapeutic options for treating infections caused by multidrug-resistant pathogens. Rational use of antibiotics requires optimisation of the pharmacokinetics and pharmacodynamics for the treatment of different types of infections. Toxicodynamics must also be considered to improve the safety of antibiotic use and, where appropriate, to guide therapeutic drug monitoring. This review focuses on the pharmacokinetics/pharmacodynamics/toxicodynamics of peptide antibiotics against multidrug-resistant Gram-negative and Gram-positive pathogens. Optimising antibiotic exposure at the infection site is essential for improving their efficacy and minimising emergence of resistance.

A synthetic lipopeptide targeting top-priority multidrug-resistant Gram-negative pathogens

The emergence of multidrug-resistant (MDR) Gram-negative pathogens is an urgent global medical challenge. The old polymyxin lipopeptide antibiotics (polymyxin B and colistin) are often the only therapeutic option due to resistance to all other classes of antibiotics and the lean antibiotic drug development pipeline. However, polymyxin B and colistin suffer from major issues in safety (dose-limiting nephrotoxicity, acute toxicity), pharmacokinetics (poor exposure in the lungs) and efficacy (negligible activity against pulmonary infections) that have severely limited their clinical utility. Here we employ chemical biology to systematically optimize multiple non-conserved positions in the polymyxin scaffold, and successfully disconnect the therapeutic efficacy from the toxicity to develop a new synthetic lipopeptide, structurally and pharmacologically distinct from polymyxin B and colistin. This resulted in the clinical candidate F365 (QPX9003) with superior safety and efficacy against lung infections caused by top-priority MDR pathogens Pseudomonas aeruginosa, Acinetobacter baumannii and Klebsiella pneumoniae.

Polymyxins are often the last therapeutic option for multidrug-resistant (MDR) bacteria, but have suboptimal safety and efficacy. Here the authors report the discovery and development of a synthetic lipopeptide with an improved safety and efficacy against top-priority MDR Gram-negative pathogens.

Case Report: Therapeutic Drug Monitoring of Polymyxin B During Continuous Renal Replacement Therapy in Two Pediatric Patients: Do Not Underestimate Extracorporeal Clearance

Background: Polymyxin B has become the last choice for patient with carbapenem-resistant bacterial infection. However, the optimal dosing of polymyxin B in critically ill children receiving continuous renal replacement therapy (CRRT) remains unclear.

Case Presentation: Two cases of critically ill pediatric patients (7 years old) with acute kidney injury requiring continuous renal replacement (CRRT) received polymyxin B treatment due to carbapenem-resistant organism bloodstream infections. Therapeutic drug monitoring (TDM) of polymyxin B was carried out by liquid chromatography tandem mass spectrometry (LC-MS/MS). The average steady-state plasma concentration (C_ss,avg) of 2–4 mg/L was set as the target level. Initial polymyxin B dose was 1 mg/kg every 12 h, and the C_ss,avg at 4–5th dosing were 1.76 and 1.06 mg/L for patient 1 and patient 2, respectively. TDM-guided polymyxin B dose was escalated to 2 mg/kg every 12 h for both patients, resulting in the C_ss,avg of 2.60 and 1.73 mg/L, and the infection was controlled subsequently. C_ss,avg of polymyxin B with the same dosing regimens and infusion length were different during CRRT and after termination of CRRT for both patients (2.60 mg/L vs. 4.94 mg/L with 2 mg/kg every 12 h in 2 h infusion for patient 1; and 1.73 mg/L vs. 3.53 mg/L with 2 mg/kg every 12 h in 2 h infusion for patient 2). The estimation of drug exposure (estimated by AUC_ss,12h at the same dose) during CRRT and cessation of CRRT showed that 45% and 51% of polymyxin B was cleared during CRRT.

Conclusion: Our study showed high clearance of polymyxin B through CRRT, and supplanted dosing of polymyxin B is necessary in pediatric patients undergoing CRRT.

Polymyxin B Combined with Minocycline: A Potentially Effective Combination against blaOXA-23-harboring CRAB in In Vitro PK/PD Model

Polymyxin-based combination therapy is commonly used to treat carbapenem-resistant Acinetobacter baumannii (CRAB) infections. In the present study, the bactericidal effect of polymyxin B and minocycline combination was tested in three CRAB strains containing bla_OXA-23 by the checkerboard assay and in vitro dynamic pharmacokinetics/pharmacodynamics (PK/PD) model. The combination showed synergistic or partial synergistic effect (fractional inhibitory concentration index ≤0.56) on the tested strains in checkboard assays. The antibacterial activity was enhanced in the combination group compared with either monotherapy in in vitro PK/PD model. The combination regimen (simultaneous infusion of 0.75 mg/kg polymyxin B and 100 mg minocycline via 2 h infusion) reduced bacterial colony counts by 0.9–3.5 log₁₀ colony forming units per milliliter (CFU/mL) compared with either drug alone at 24 h. In conclusion, 0.75 mg/kg polymyxin B combined with 100 mg minocycline via 2 h infusion could be a promising treatment option for CRAB bloodstream infections.

Pharmacokinetic/Pharmacodynamic Based Breakpoints of Polymyxin B for Bloodstream Infections Caused by Multidrug-Resistant Gram-Negative Pathogens

The latest PK/PD findings have demonstrated negligible efficacy of intravenous polymyxins against pulmonary infections. We investigated pharmacokinetic/pharmacodynamic (PK/PD)-based breakpoints of polymyxin B for bloodstream infections and the rationality of the recent withdrawal of polymyxin susceptibility breakpoints by the CLSI. Polymyxin B pharmacokinetic data were obtained from a phase I clinical trial in healthy Chinese subjects and population pharmacokinetic parameters were employed to determine the exposure of polymyxin B at steady state. MICs of 1,431 recent clinical isolates of Pseudomonas aeruginosa, Acinetobacter baumannii and Klebsiella pneumoniae collected from across China were determined. Monte-Carlo simulations were performed for various dosing regimens (0.42–1.5 mg/kg/12 h via 1 or 2-h infusion). The probability of target attainment, PK/PD breakpoints and cumulative fraction of response were determined for each bacterial species. MIC₉₀ of polymyxin B was 1 mg/L for P. aeruginosa and 0.5 mg/L for A. baumannii and K. pneumoniae. With the recommended polymyxin B dose of 1.5–2.5 mg/kg/day, the PK/PD susceptible breakpoints for P. aeruginosa, A. baumannii and K. pneumoniae were 2, 1 and 1 mg/L respectively for bloodstream infection. For Chinese patients, polymyxin B dosing regimens of 0.75–1.5 mg/kg/12 h for P. aeruginosa and 1–1.5 mg/kg/12 h for A. baumannii and K. pneumoniae were appropriate. Breakpoint determination should consider the antimicrobial PK/PD at infection site and delivery route. The recent withdrawal of polymyxin susceptible breakpoint by CLSI primarily based on poor efficacy against lung infections needs to be reconsidered for bloodstream infections.

The Monte Carlo Simulation of Three Antimicrobials for Empiric Treatment of Adult Bloodstream Infections With Carbapenem-Resistant Enterobacterales in China

Introduction: The aim of this study was to predict and evaluate three antimicrobials for treatment of adult bloodstream infections (BSI) with carbapenem-resistant Enterobacterales (CRE) in China, so as to optimize the clinical dosing regimen further.

Methods: Antimicrobial susceptibility data of blood isolates were obtained from the Blood Bacterial Resistance Investigation Collaborative Systems in China. Monte Carlo simulation was conducted to estimate the probability target attainment (PTA) and cumulative fraction of response (CFR) of tigecycline, polymyxin B, and ceftazidime/avibactam against CRE.

Results: For the results of PTAs, tigecycline following administration of 50 mg every 12 h, 75 mg every 12 h, and 100 mg every 12 h achieved > 90% PTAs when minimum inhibitory concentration (MIC) was 0.25, 0.5, and 0.5 μg/mL, respectively; polymyxin B following administration of all tested regimens achieved > 90% PTAs when MIC was 1 μg/mL with CRE; ceftazidime/avibactam following administration of 1.25 g every 8 h, 2.5 g every 8 h achieved > 90% PTAs when MIC was 4 μg/mL, 8 μg/mL with CRE, respectively. As for CFR values of three antimicrobials, ceftazidime/avibactam achieved the lowest CFR values. The highest CFR value of ceftazidime/avibactam was 77.42%. For tigecycline and ceftazidime/avibactam, with simulated regimens daily dosing increase, the CFR values were both increased; the highest CFR of tigecycline values was 91.88%. For polymyxin B, the most aggressive dosage of 1.5 mg/kg every 12 h could provide the highest CFR values (82.69%) against CRE.

Conclusion: This study suggested that measurement of MICs and individualized therapy should be considered together to achieve the optimal drug exposure. In particular, pharmacokinetic and pharmacodynamic modeling based on local antimicrobial resistance data can provide valuable guidance for clinicians for the administration of empirical antibiotic treatments for BSIs.

Visualizing the Potential Impairment of Polymyxin B to Central Nervous System Through MR Susceptibility-Weighted Imaging

Polymyxin B (PMB) exert bactericidal effects on the cell wall of Gram-negative bacteria, leading to changes in the permeability of the cytoplasmic membrane and resulting in cell death, which is sensitive to the multi-resistant Gram-negative bacteria. However, the severe toxicity and adverse side effects largely hamper the clinical application of PMB. Although the molecular pathology of PMB neurotoxicity has been adequately studied at the cellular and molecular level. However, the impact of PMB on the physiological states of central nervous system in vivo may be quite different from that in vitro, which need to be further studied. Therefore, in the current study, the biocompatible ultra-uniform Fe3O4 nanoparticles were employed for noninvasively in vivo visualizing the potential impairment of PMB to the central nervous system. Systematic studies clearly reveal that the prepared Fe3O4 nanoparticles can serve as an appropriate magnetic resonance contrast agent with high transverse relaxivity and outstanding biosafety, which thus enables the following in vivo susceptibility-weighted imaging (SWI) studies on the PMB-treated mice models. As a result, it is first found that the blood-brain barrier (BBB) of mice may be impaired by successive PMB administration, displaying by the discrete punctate SWI signals distributed asymmetrically across brain regions in brain parenchyma. This result may pave a noninvasive approach for in-depth studies of PMB medication strategy, monitoring the BBB changes during PMB treatment, and even assessing the risk after PMB successive medication in multidrug-resistant Gram-negative bacterial infected patients from the perspective of medical imaging.