Chemotherapy in pediatric brain tumor and the challenge of the blood-brain barrier

BACKGROUND

Pediatric brain tumors (PBT) stand as the leading cause of cancer-related deaths in children. Chemoradiation protocols have improved survival rates, even for non-resectable tumors. Nonetheless, radiation therapy carries the risk of numerous adverse effects that can have long-lasting, detrimental effects on the quality of life for survivors. The pursuit of chemotherapeutics that could obviate the need for radiotherapy remains ongoing. Several anti-tumor agents, including sunitinib, valproic acid, carboplatin, and panobinostat, have shown effectiveness in various malignancies but have not proven effective in treating PBT. The presence of the blood-brain barrier (BBB) plays a pivotal role in maintaining suboptimal concentrations of anti-cancer drugs in the central nervous system (CNS). Ongoing research aims to modulate the integrity of the BBB to attain clinically effective drug concentrations in the CNS. However, current findings on the interaction of exogenous chemical agents with the BBB remain limited and do not provide a comprehensive explanation for the ineffectiveness of established anti-cancer drugs in PBT.

METHODS

We conducted our search for chemotherapeutic agents associated with the blood-brain barrier (BBB) using the following keywords: Chemotherapy in Cancer, Chemotherapy in Brain Cancer, Chemotherapy in PBT, BBB Inhibition of Drugs into CNS, Suboptimal Concentration of CNS Drugs, PBT Drugs and BBB, and Potential PBT Drugs. We reviewed each relevant article before compiling the information in our manuscript. For the generation of figures, we utilized BioRender software.

FOCUS

We focused our article search on chemical agents for PBT and subsequently investigated the role of the BBB in this context. Our search criteria included clinical trials, both randomized and non-randomized studies, preclinical research, review articles, and research papers.

FINDING

Our research suggests that, despite the availability of potent chemotherapeutic agents for several types of cancer, the effectiveness of these chemical agents in treating PBT has not been comprehensively explored. Additionally, there is a scarcity of studies examining the role of the BBB in the suboptimal outcomes of PBT treatment, despite the effectiveness of these drugs for other types of tumors.

Quantification of nine antiretroviral drugs in cerebrospinal fluid: An approach to overcome sample collection tube adsorption

A highly sensitive LC-MS/MS methods were developed and validated to quantify nine antiretrovirals (atazanavir [ATV], tenofovir [TFV], emtricitabine [FTC], darunavir [DRV], dolutegravir [DTG], efavirenz [EFV], lamivudine [3TC], raltegravir [RAL], and ritonavir [RTV]) in human cerebral spinal fluid (CSF). The approach remedies adsorption issues caused by polypropylene based sample collection tubes. 1% ammonium hydroxide in methanol was added in an amount equal to the volume of each quality control (QC) or patient sample. Protein precipitation was utilized with a CSF sample volume of 100 μL and a 100 μL of methanol:ACN and vortexed. Chromatographic separation was achieved with a 3 × 100 ACE® C18 column for ATV, DRV, DTG, EFV, RTV and RAL, and a 2 × 100 Polar RP column for TFV/FTC/3TC. Mobile phase was methanol:water:formic acid (70:30:0.1, v/v/v) for ATV, DRV, DTG, EFV and RTV (10 uL injection, flow rate: 1.00 mL/min), ACN:water:formic acid (35:65:0.1, v/v/v) for RAL (50 uL injection, flow rate: 1.00 mL/min), ACN:water:formic acid (2:98:0.1, v/v/v) for TFV, FTC and 3TC (50 uL injection, flow rate: 0.35 mL/min). Column temperature was 40° C across all assays. The mass spectrometer was operated in positive, multiple-reaction-monitoring (MRM) mode with electrospray ionization (ESI) for all analytes with the exception of EFV, which was operated in negative, MRM mode with ESI. The assay was linear over the calibration range of 1 to 250 ng/mL for all analytes. The addition of 1% ammonium hydroxide in sample tubes overcame up to 44% negative bias in QC samples and allowed the methods to meet full validation criteria.

ACE-2, TMPRSS2, and Neuropilin-1 Receptor Expression on Human Brain Astrocytes and Pericytes and SARS-CoV-2 Infection Kinetics

Angiotensin Converting Enzyme 2 (ACE-2), Transmembrane Serine Protease 2 (TMPRSS-2) and Neuropilin-1 cellular receptors support the entry of SARS-CoV-2 into susceptible human target cells and are characterized at the molecular level. Some evidence on the expression of entry receptors at mRNA and protein levels in brain cells is available, but co-expression of these receptors and confirmatory evidence on brain cells is lacking. SARS-CoV-2 infects some brain cell types, but infection susceptibility, multiple entry receptor density, and infection kinetics are rarely reported in specific brain cell types. Highly sensitive Taqman ddPCR, flow-cytometry and immunocytochemistry assays were used to quantitate the expression of ACE-2, TMPRSS-2 and Neuropilin-1 at mRNA and protein levels on human brain-extracted pericytes and astrocytes, which are an integral part of the Blood-Brain-Barrier (BBB). Astrocytes showed moderate ACE-2 (15.9 ± 1.3%, Mean ± SD, n = 2) and TMPRSS-2 (17.6%) positive cells, and in contrast show high Neuropilin-1 (56.4 ± 39.8%, n = 4) protein expression. Whereas pericytes showed variable ACE-2 (23.1 ± 20.7%, n = 2), Neuropilin-1 (30.3 ± 7.5%, n = 4) protein expression and higher TMPRSS-2 mRNA (667.2 ± 232.3, n = 3) expression. Co-expression of multiple entry receptors on astrocytes and pericytes allows entry of SARS-CoV-2 and progression of infection. Astrocytes showed roughly four-fold more virus in culture supernatants than pericytes. SARS-CoV-2 cellular entry receptor expression and "in vitro" viral kinetics in astrocytes and pericytes may improve our understanding of viral infection "in vivo". In addition, this study may facilitate the development of novel strategies to counter the effects of SARS-CoV-2 and inhibit viral infection in brain tissues to prevent the spread and interference in neuronal functions.

A novel 4-cell in-vitro blood-brain barrier model and its characterization by confocal microscopy and TEER measurement

The blood-brain barrier (BBB) is a protective cellular anatomical layer with a dynamic micro-environment, tightly regulating the transport of materials across it. To achieve in-vivo characteristics, an in-vitro BBB model requires the constituent cell types to be layered in an appropriate order. A cost-effective in-vitro BBB model is desired to facilitate central nervous system (CNS) drug penetration studies. Enhanced integrity of tight junctions observed during the in-vitro BBB establishment and post-experiment is essential in these models. We successfully developed an in-vitro BBB model mimicking the in-vivo cell composition and a distinct order of seeding primary human brain cells. Unlike other in-vitro BBB models, our work avoids the need for pre-coated plates for cell adhesion and provides better cell visualization during the procedure. We found that using bovine collagen-I coating, followed by bovine fibronectin coating and poly-L-lysine coating, yields better adhesion and layering of cells on the transwell membrane compared to earlier reported use of collagen and poly-L-lysine only. Our results indicated better cell visibility and imaging with the polyester transwell membrane as well as point to a higher and more stable Trans Endothelial Electrical Resistance values in this plate. In addition, we found that the addition of zinc induced higher claudin 5 expressions in neuronal cells. Dolutegravir, a drug used in the treatment of HIV, is known to appear in moderate concentrations in the CNS. Thus, dolutegravir was used to assess the functionality of the final model and cells. Using primary cells and an in-house coating strategy substantially reduces costs and provides superior imaging of cells and their tight junction protein expression. Our 4-cell-based BBB model is a suitable experimental model for the drug screening process.

Transformation of dolutegravir into an ultra-long-acting parenteral prodrug formulation

Ultra-long-acting integrase strand transfer inhibitors were created by screening a library of monomeric and dimeric dolutegravir (DTG) prodrug nanoformulations. This led to an 18-carbon chain modified ester prodrug nanocrystal (coined NM2DTG) with the potential to sustain yearly dosing. Here, we show that the physiochemical and pharmacokinetic (PK) formulation properties facilitate slow drug release from tissue macrophage depot stores at the muscle injection site and adjacent lymphoid tissues following single parenteral injection. Significant plasma drug levels are recorded up to a year following injection. Tissue sites for prodrug hydrolysis are dependent on nanocrystal dissolution and prodrug release, drug-depot volume, perfusion, and cell-tissue pH. Each affect an extended NM2DTG apparent half-life recorded by PK parameters. The NM2DTG product can impact therapeutic adherence, tolerability, and access of a widely used integrase inhibitor in both resource limited and rich settings to reduce HIV-1 transmission and achieve optimal treatment outcomes.

Lack of synergistic nephrotoxicity between vancomycin and piperacillin/tazobactam in a rat model and a confirmatory cellular model

BACKGROUND

Vancomycin and piperacillin/tazobactam are reported in clinical studies to increase acute kidney injury (AKI). However, no clinical study has demonstrated synergistic toxicity, only that serum creatinine increases.

OBJECTIVES

To clarify the potential for synergistic toxicity between vancomycin, piperacillin/tazobactam and vancomycin + piperacillin/tazobactam treatments by quantifying kidney injury in a translational rat model of AKI and using cell studies.

METHODS

(i) Male Sprague-Dawley rats (n = 32) received saline, vancomycin 150 mg/kg/day intravenously, piperacillin/tazobactam 1400 mg/kg/day intraperitoneally or vancomycin + piperacillin/tazobactam for 3 days. Urinary biomarkers and histopathology were analysed. (ii) Cellular injury was assessed in NRK-52E cells using alamarBlue®.

RESULTS

Urinary output increased from Day -1 to Day 1 with vancomycin but only after Day 2 for vancomycin + piperacillin/tazobactam-treated rats. Plasma creatinine was elevated from baseline with vancomycin by Day 2 and only by Day 4 for vancomycin + piperacillin/tazobactam. Urinary KIM-1 and clusterin were increased with vancomycin from Day 1 versus controls (P < 0.001) and only on Day 3 with vancomycin + piperacillin/tazobactam (P < 0.001, KIM-1; P < 0.05, clusterin). The histopathology injury score was elevated only in the vancomycin group when compared with piperacillin/tazobactam as a control (P = 0.04) and generally not so with vancomycin + piperacillin/tazobactam. In NRK-52E cells, vancomycin induced cell death with high doses (IC50 48.76 mg/mL) but piperacillin/tazobactam did not, and vancomycin + piperacillin/tazobactam was similar to vancomycin.

CONCLUSIONS

All groups treated with vancomycin demonstrated AKI; however, vancomycin + piperacillin/tazobactam was not worse than vancomycin. Histopathology suggested that piperacillin/tazobactam did not worsen vancomycin-induced AKI and may even be protective.

Role of toll-like receptor 7/8 pathways in regulation of interferon response and inflammatory mediators during SARS-CoV2 infection and potential therapeutic options

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV2) is the causative agent of Corona Virus Disease 2019 (COVID-19). Lower production of type I and III interferons and higher levels of inflammatory mediators upon SARS-CoV2 infection contribute to COVID-19 pathogenesis. Optimal interferon production and controlled inflammation are essential to limit COVID-19 pathogenesis. However, the aggravated inflammatory response observed in COVID-19 patients causes severe damage to the host and frequently advances to acute respiratory distress syndrome (ARDS). Toll-like receptor 7 and 8 (TLR7/8) signaling pathways play a central role in regulating induction of interferons (IFNs) and inflammatory mediators in dendritic cells. Controlled inflammation is possible through regulation of TLR mediated response without influencing interferon production to reduce COVID-19 pathogenesis. This review focuses on inflammatory mediators that contribute to pathogenic effects and the role of TLR pathways in the induction of interferon and inflammatory mediators and their contribution to COVID-19 pathogenesis. We conclude that potential TLR7/8 agonists inducing antiviral interferon response and controlling inflammation are important therapeutic options to effectively eliminate SARS-CoV2 induced pathogenesis. Ongoing and future studies may provide additional evidence on their safety and efficacy to treat COVID-19 pathogenesis.

Augmented renal clearance of aminoglycosides using population-based pharmacokinetic modelling with Bayesian estimation in the paediatric ICU

OBJECTIVE

To evaluate augmented renal clearance (ARC) using aminoglycoside clearance (CLAMINO24h) derived from pharmacokinetic (PK) modelling.

METHODS

A retrospective study at two paediatric hospitals of patients who received tobramycin or gentamicin from 1999 to 2016 was conducted. Compartmental PK models were constructed using the Pmetrics package, and Bayesian posteriors were used to estimate CLAMINO24h. ARC was defined as a CLAMINO24h of ≥130 mL/min/1.73 m2. Risk factors for ARC were identified using multivariate logistic regression.

RESULTS

The final population model was fitted to 275 aminoglycoside serum concentrations. Overall clearance (L/h) was=CL0×(TBW/70)0.75×AGEH/(TMH + AGEH) + CL1 (0.5/SCr), where TBW is total body weight, H is the Hill coefficient, TM is a maturation term and SCr is serum creatinine. Median CLAMINO24h in those with versus without ARC was 157.36 and 93.42 mL/min/1.73 m2, respectively (P<0.001). ARC was identified in 19.5% of 118 patients. For patients with ARC, median baseline SCr was lower than for those without ARC (0.38 versus 0.41 mg/dL, P=0.073). Risk factors for ARC included sepsis [adjusted OR (aOR) 3.77, 95% CI 1.01-14.07, P=0.048], increasing age (aOR 1.11, 95% CI 1-1.23, P=0.04) and low log-transformed SCr (aOR 0.16, 95% CI 0.05-0.52, P=0.002). Median 24 h AUC (AUC24h) was significantly lower in patients with ARC at 45.27 versus 56.95 mg·h/L, P<0.01.

CONCLUSIONS

ARC was observed in one of every five patients. Sepsis, increasing age and low SCr were associated with ARC. Increased clearance was associated with an attenuation of AUC24h in this population. Future studies are needed to define optimal dosing in paediatric patients with ARC.

Antimicrobial prescribing for treatment of serious infections caused by Staphylococcus aureus and methicillin-resistant Staphylococcus aureus in pediatrics: an expert review

Introduction: Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA), remains a significant pathogen in children. Despite evidence of decreasing prevalence, MRSA bacteremia has been closely associated with complications, including certain infections (i.e. musculoskeletal and endovascular) linked to increased treatment failures.Areas covered: This expert review summarized recent published literature on the role of treatment, dosing and administration of antibiotics used to combat serious S. aureus infections in children. The pertinent antibiotics presented were vancomycin, oxazolidinones, semi-synthetic glycopeptides, daptomycin, tigecycline, novel cephalosporins, fosfomycin and lefamulin. Vancomycin has been the most commonly used antibiotic in empiric therapy for serious MRSA infection, with new key recommendations emphasizing a different approach to dosing and therapeutic monitoring. For other antibiotics, data remain limited or clinical trials are underway.Expert opinion: MRSA remains a significant pathogen in the pediatric population. As numerous therapeutic agents are available, many agents have limited data on usage in pediatric patients. Future studies require pharmacokinetic, safety and efficacy studies in pediatric patients to ensure appropriate therapeutic treatment and outcomes. Phage therapy has been used to treat deep-seated MRSA infections and is an emerging investigational treatment option.

HIV-1 Integrase Inhibitors: A Comparative Review of Efficacy and Safety

The newest class of antiretrovirals for all persons living with HIV are the integrase strand transfer inhibitors (INSTIs). Since 2007, five INSTIs have been introduced: raltegravir, elvitegravir, dolutegravir, bictegravir, and cabotegravir. The INSTIs have favorable pharmacokinetic and pharmacodynamic properties, which contribute to both their effectiveness and their ease of use. With the exception of cabotegravir, each INSTI is US Food and Drug Administration approved for treatment-naïve individuals initiating antiretroviral therapy. All of the INSTIs, except raltegravir, are approved for antiretroviral treatment simplification for virologically suppressed patients without INSTI resistance. Data also support the use of dolutegravir and raltegravir in individuals with antiretroviral resistance as part of an optimized antiretroviral regimen. INSTIs are generally well tolerated by people living with HIV compared with older classes of antiretrovirals, but emerging data suggest that some INSTIs contribute to weight gain. Due to their efficacy, safety, and ease of use, HIV treatment guidelines recommend oral INSTIs as preferred components of antiretroviral therapy for individuals initiating therapy. The newest INSTI, cabotegravir, represents an alternative to oral administration of life-long antiretroviral therapy with the availability of a long-acting injectable formulation. This review summarizes the current use of INSTIs in adults living with HIV, highlighting the similarities and differences within the class related to pharmacodynamics, pharmacokinetics, safety, dosing, and administration that contribute to their role in modern antiretroviral therapy.

Pharmacologic approaches to HIV-associated neurocognitive disorders

Antiretroviral therapy in people living with HIV can achieve potent, long-term suppression of HIV plasma viremia and has increased life expectancy. The central nervous system is infected early after virus acquisition and remains a reservoir for HIV. HIV-associated neurocognitive disorders (HAND) are an end-organ manifestation of HIV infection. The need to address neurological complications caused by HAND is significant as approximately 50% of people living with HIV on suppressive antiretroviral therapy are estimated to have some form of HAND. This review discusses the pathophysiology of HAND, CSF/CNS penetration and clinical pharmacology of antiretrovirals including pharmacokinetic/pharmacodynamic relationships, the persistence of HIV in the brain, and future therapeutic approaches to preserve and improve sustained viral suppression in the brain.

Twenty-four hour pharmacokinetic relationships for intravenous vancomycin and novel urinary biomarkers of acute kidney injury in a rat model

OBJECTIVES

To identify the pharmacokinetic (PK) and toxicodynamic (TD) relationship for vancomycin-induced kidney injury.

METHODS

Male Sprague-Dawley rats received intravenous (iv) vancomycin. Doses ranging from 150 mg/kg/day to 400 mg/kg/day were administered as a single or twice-daily injection over 24 h (total protocol duration). Controls received iv saline. Plasma was sampled with up to eight samples in 24 h per rat. Twenty-four hour urine was collected and assayed for kidney injury molecule 1 (KIM-1), osteopontin and clusterin. Vancomycin in plasma was quantified via LC-MS/MS. PK analyses were conducted using Pmetrics for R. PK exposures during the first 24 h (i.e. AUC0-24h, Cmax 0-24h and Cmin 0-24h) were calculated. PK/TD relationships were assessed with Spearman's rank coefficient (rs) and the best-fit mathematical model.

RESULTS

PK/TD data were generated from 45 vancomycin-treated and 5 control rats. A two-compartment model fit the data well (Bayesian: observed versus predicted R2 = 0.97). Exposure-response relationships were found between AUC0-24h versus KIM-1 and osteopontin (R2 = 0.61 and 0.66) and Cmax 0-24h versus KIM-1 and osteopontin (R2 = 0.50 and 0.56) using a four-parameter Hill fit. Conversely, Cmin 0-24h was less predictive of KIM-1 and osteopontin (R2 = 0.46 and 0.53). A vancomycin AUC0-24h of 482.2 corresponded to a 90% of maximal rise in KIM-1.

CONCLUSIONS

Vancomycin-induced kidney injury as defined by urinary biomarkers is driven by vancomycin AUC or Cmax rather than Cmin. Further, an identified PK/TD target AUC0-24h of 482.2 mg·h/L may have direct relevance to human outcomes.

Use of Simulation Strategies to Predict Subtherapeutic Meropenem Exposure Caused by Augmented Renal Clearance in Critically Ill Pediatric Patients With Sepsis

OBJECTIVES

The objectives of this study were to 1) define extent and potential clinical impact of increased or decreased renal elimination of meropenem in children with sepsis, based on analysis of renal function during the first 2 days of PICU stay; and 2) estimate the risk of subtherapeutic meropenem exposure attributable to increased renal clearance.

METHODS

This retrospective study evaluated patients with a diagnosis of sepsis, receiving meropenem from the PICU at Rady Children's Hospital San Diego from 2015-2017. Meropenem exposure was estimated by using FDA-approved doses (20 and 40 mg/kg/dose) on day 1 and day 2 of PICU stay, based on a population pharmacokinetic (PK) model. For this population with sepsis, we assessed time-above-minimum inhibitory concentration (T>MIC) for pathogen MICs.

RESULTS

Meropenem treatment was documented in 105 episodes of sepsis with a 48% rate of pathogen detection. By day 2, increased eGFR (>120 mL/min/1.73 m²) was documented in 49% of patients, with 17% meeting criteria for augmented renal clearance ([ARC] >160 mL/min/1.73 m²) and 10%, for decreased function. Simulations documented that 80% of PICU patients with ARC did not achieve therapeutic meropenem exposure for Pseudomonas aeruginosa with a MIC of 2, using standard doses to achieve a pharmacodynamic goal of 80% T>MIC.

CONCLUSIONS

Approximately 3 of every 20 children with sepsis exhibited ARC during the first 48 hours of PICU stay. Simulations documented an increased risk for subtherapeutic meropenem exposure, suggesting that higher meropenem doses may be required to achieve adequate antibiotic exposure early in the PICU course.

Pharmacokinetic Assessment of Pre- and Post-Oxygenator Vancomycin Concentrations in Extracorporeal Membrane Oxygenation: A Prospective Observational Study

BACKGROUND

Extracorporeal membrane oxygenation (ECMO) is a form of cardiopulmonary life support frequently utilized in catastrophic lung and or cardiac failure. Patients on ECMO often receive vancomycin therapy for treatment or prophylaxis against Gram-positive organisms. It is unclear if ECMO affects vancomycin pharmacokinetics, thus we modeled the pharmacokinetic behavior of vancomycin according to ECMO-specific variables.

METHODS

Adult patients receiving vancomycin and Veno-Arterial-ECMO between 12/1/2016 and 10/1/2017 were prospectively enrolled. Extracorporeal membrane oxygenation settings and four sets of pre- and post-oxygenator vancomycin concentrations were collected for each patient. Compartmental models were built and assessed ECMO flow rates on vancomycin clearance and potential circuit sequestration. Bayesian posterior concentrations of the pre- and post-oxygenator concentrations were obtained for each patient, and summary pharmacokinetic parameters were calculated. Simulations were performed from the final model for efficacy and toxicity predictions.

RESULTS

Eight patients contributed 64 serum concentrations. Patients were a median (interquartile range) age of 58.5 years (50.8-62.3) with a calculated creatinine clearance of 39 mL/min (29.5-62.5) and ECMO flow rates of 3980 mL/min (interquartile range = 3493.75-4132.5). A three-compartment model best fit the data (Bayesian: plasma pre-oxygenation R² = 0.99, post-oxygenation R² = 0.99). Vancomycin clearance was not impacted by ECMO flow rate (p = 0.7). Simulations demonstrated that vancomycin 1 g twice daily was rarely sufficient for minimum inhibitory concentrations > 0.5 mg/L. Doses ≥ 1.5 g twice daily often exceeded toxicity thresholds for exposure.

CONCLUSIONS

Extracorporeal membrane oxygenation flow rates did not influence vancomycin clearance between flow rates of 3500 and 5000 mL/min and vancomycin was not sequestered in ECMO. Common vancomycin regimens resulted in suboptimal efficacy and/or excessive toxicity. Individual therapeutic drug monitoring is recommended for patients on ECMO.

Vancomycin-Induced Kidney Injury: Animal Models of Toxicodynamics, Mechanisms of Injury, Human Translation, and Potential Strategies for Prevention

Vancomycin is a recommended therapy in multiple national guidelines. Despite the common use, there is a poor understanding of the mechanistic drivers and potential modifiers of vancomycin-mediated kidney injury. In this review, historic and contemporary rates of vancomycin-induced kidney injury (VIKI) are described, and toxicodynamic models and mechanisms of toxicity from preclinical studies are reviewed. Aside from known clinical covariates that worsen VIKI, preclinical models have demonstrated that various factors impact VIKI, including dose, route of administration, and thresholds for pharmacokinetic parameters. The degree of acute kidney injury (AKI) is greatest with the intravenous route and higher doses that produce larger maximal concentrations and areas under the concentration curve. Troughs (i.e., minimum concentrations) have less of an impact. Mechanistically, preclinical studies have identified that VIKI is a result of drug accumulation in proximal tubule cells, which triggers cellular oxidative stress and apoptosis. Yet, there are several gaps in the knowledge that may represent viable targets to make vancomycin therapy less toxic. Potential strategies include prolonging infusions and lowering maximal concentrations, administration of antioxidants, administering agents that decrease cellular accumulation, and reformulating vancomycin to alter the renal clearance mechanism. Based on preclinical models and mechanisms of toxicity, we propose potential strategies to lessen VIKI.

Evaluation of Dose-Fractionated Polymyxin B on Acute Kidney Injury Using a Translational In Vivo Rat Model

We investigated dose-fractionated polymyxin B (PB) on acute kidney injury (AKI). PB at 12 mg of drug/kg of body weight per day (once, twice, and thrice daily) was administered in rats over 72 h. The thrice-daily group demonstrated the highest KIM-1 increase (P = 0.018) versus that of the controls (P = 0.99) and histopathological damage (P = 0.013). A three-compartment model best described the data (bias, 0.129 mg/liter; imprecision, 0.729 mg2/liter2; R2, 0.652,). Area under the concentration-time curve at 24 h (AUC24) values were similar (P = 0.87). The thrice-daily dosing scheme resulted in the most PB-associated AKI in a rat model.

Piperacillin-Tazobactam Added to Vancomycin Increases Risk for Acute Kidney Injury: Fact or Fiction?

Vancomycin and piperacillin-tazobactam are 2 of the most commonly prescribed antibiotics in hospitals. Recent data from multiple meta-analyses suggest that the combination increases the risk for vancomycin-induced kidney injury when compared to alternative viable options. However, these studies are unable to prove biologic plausibility and causality as randomized controlled trials have not been performed. Furthermore, these studies define acute kidney injury according to thresholds of serum creatinine rise. Serum creatinine is not a direct indicator of renal injury, rather a surrogate of glomerular function. More reliable, specific, and sensitive biomarkers are needed to truly define if there is a causal relationship with increased toxicity when piperacillin-tazobactam is added to vancomycin. This viewpoint will explore the available evidence for and against increased acute kidney injury in the setting of vancomycin and piperacillin-tazobactam coadministration.

Vancomycin Area Under the Curve and Acute Kidney Injury: A Meta-analysis

BACKGROUND

This study analyzed the relationship between vancomycin area under the concentration-time curve (AUC) and acute kidney injury (AKI) reported across recent studies.

METHODS

A systematic review of PubMed, Medline, Scopus, and compiled references was conducted. We included randomized cohort and case-control studies that reported vancomycin AUCs and risk of AKI (from 1990 to 2018). The primary outcome was AKI, defined as an increase in serum creatinine of ≥0.5 mg/L or a 50% increase from baseline on ≥2 consecutive measurements. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated. Primary analyses compared the impact of AUC cutpoint (greater than ~650 mg × hour/L) and AKI. Additional analysis compared AUC vs trough-guided monitoring on AKI incidence.

RESULTS

Eight observational studies met inclusion/exclusion criteria with data for 2491 patients. Five studies reported first-24-hour AUCs (AUC0-24) and AKI, 2 studies reported 24- to 48-hour AUCs (AUC24-48) and AKI, and 2 studies reported AKI associated with AUC- vs trough-guided monitoring. AUC less than approximately 650 mg × hour/L was associated with decreased AKI for AUC0-24 (OR, 0.36 [95% CI, .23-.56]) as well as AUC24-48 (OR, 0.45 [95% CI, .27-.75]). AKI associated with the AUC monitoring strategy was significantly lower than trough-guided monitoring (OR, 0.68 [95% CI, .46-.99]).

CONCLUSIONS

AUCs measured in the first or second 24 hours and lower than approximately 650 mg × hour/L may result in a decreased risk of AKI. Vancomycin AUC monitoring strategy may result in less vancomycin-associated AKI. Additional investigations are warranted.

1569. A Translational Model to Assess the Impact of Polymyxin B Dose Fractionation on Kidney Injury

Background

Progression of antimicrobial resistance has revived Polymyxin B (PB) use in clinical practice. Dose-dependent acute kidney injury (AKI) limits its clinical use. It is unclear whether dose fractionation of total daily dose can lessen kidney injury. We assessed the role of PB fractionation on AKI in a translational model that employs sensitive urine biomarkers qualified by the FDA.

Methods

Male Sprague–Dawley rats received 12 mg/kg/day PB subcutaneously for 3 days or equal-volume normal saline (NS). PB was administered in 3 separate fractionated daily doses: 12 mg/kg daily (QD), 6 mg/kg twice daily (BID), and 4 mg/kg thrice daily (TID). Staggered blood sampling was done on days 1 to 4 and 24 hour urine was collected at baseline, on days 1, 2, and 3. Plasma creatinine (Cr) was quantified using LCMS/MS, and 24 hour urinary biomarkers (KIM1, OPN, CLN, calbindin, GSTα, IP-10, TIMP-1, and VEGF) were assayed with MILLIPLEX Rat Kidney Toxicity Magnetic Bead Panel. Mixed-effects models were used.

Results

A total of 32 rats contributed to the study data. Mean Cr were constant across groups over time (Figure 1, P = 0.18). For NS group, all biomarkers remained at baseline throughout study. Significant differences were seen for fractionation schemes for KIM1 (P = 0.02), CLN (P = 0.03), IP-10 (0.007) and TIMP-1 (P = 0.04). The differences for KIM1, IP-10, and TIMP-1 were driven by higher observed values in TID than those of BID as early as day 1 (P < 0.04). Furthermore, CLN was elevated for TID when compared with BID at baseline (P = 0.048). Similarly, TID group had the highest (but non-significant) elevations for IP-10 and TIMP-1 compared with QD on study days. Amongst all urine biomarkers, KIM1 in TID exhibited the most rapid rise from baseline to day 2 (Figure2, P < 0.0001).

Conclusion

In this translational model in which a single total daily dose was fractionated, sensitive urinary biomarkers indicated that TID dosing was worse than BID or QD dosing; dose fractionation of PB may lead to increased AKI. In addition, KIM1 rose rapidly as an early marker for AKI. Further efforts are needed to investigate the PK-TD relationship of PB in order to decrease AKI.

Disclosures

All authors: No reported disclosures.

1335. A Translational Nephrotoxicity Model to Probe Acute Kidney Injury with Vancomycin and Piperacillin–Tazobactam

Background

Vancomycin and piperacillin–tazobactam (VAN+TZP) are two of the most commonly utilized antibiotics in the hospital setting and are reported in clinical studies to increase acute kidney injury (AKI). However, no clinical study has demonstrated that synergistic AKI occurs, only that serum creatinine increases with VAN+TZP. Previous preclinical work demonstrated that novel urinary biomarkers and histopathologic scores were not increased in the VAN+TZP group compared with VAN alone. The purpose of this study was to assess changes in urinary output and plasma creatinine between VAN, TZP, and VAN+TZP treatments.

Methods

Male Sprague–Dawley rats (n = 32) received either saline, VAN 150 mg/kg/day intravenously, TZP 1,400 mg/kg/day intraperitoneally, or VAN+TZP for 3 days. Animals were placed in metabolic cages pre-study and on drug dosing days 1–3. Urinary output, plasma creatinine, urinary biomarkers were compared daily and kidney histopathology was compared at the end of therapy between the groups. Mixed-effects, repeated-measures models were employed to assess differences between the groups.

Results

In the VAN-treated rats, urinary output was increased on days 1, 2 and 3 compared with baseline and saline (P < 0.01 for all), whereas it increased later for VAN+TZP (i.e., day 2 and 3 compared with saline, P < 0.001). No changes in urinary output were observed with saline and TZP alone. Plasma creatinine rose for VAN on days 1, 2, and 3 from baseline and VAN+TZP on day 3 (P < 0.02 for all), but no treatment group was different from saline. In the VAN-treated rats, urinary KIM-1 and clusterin were increased on days 1, 2, and 3 compared with controls (P < 0.001). Elevations were seen only after 3 days of treatment with VAN+TZP (P < 0.001 KIM-1, P < 0.05 clusterin). No changes in urinary biomarkers output were observed with saline and TZP alone. Histopathology was only elevated in the VAN group compared with saline (P < 0.002). No histopathology changes were noted with VAN+TZP.

Conclusion

All groups with VAN demonstrated kidney injury; however, VAN+TZP did not cause more kidney injury than VAN alone in a rat model of VIKI when using plasma creatinine, urinary output, or urinary biomarkers as outcomes. Histopathology data suggest that adding TZP did not worsen VAN-induced AKI and may even be protective.

Disclosures

Kevin J. Downes, MD, Merck: Grant/Research Support, Research Grant; Pfizer: Grant/Research Support.

1568. The Pharmacodynamic–Toxicodynamic Relationship of AUC and CMAX in Vancomycin-Induced Kidney Injury

Background

Vancomycin induces exposure-related acute kidney injury [AKI]; yet the toxicodynamic (TD) driver for toxicity (area under the curve [AUC], vs. maximum concentration [CMAX] vs. trough concentrations [CMIN]) remains unclear. Recent vancomycin guidelines now recommend monitoring AUC over troughs. Here we employed our translational rat model with intensive dose fractionation and sensitive FDA qualified urinary biomarkers to better understand TD relationship.

Methods

Male Sprague-Dawley rats received intravenous (IV) vancomycin via an internal jugular vein catheter. Total daily doses of 300 and 400 mg/kg/day were administered as a single, twice, thrice and four times a day injection over 24 hours. Controls received IV saline. Plasma sampling was conducted via a second dedicated jugular catheter, with up to 8 samples in 24 hours. Twenty-four-hour urine was collected during this time and assayed for kidney injury molecule 1 (KIM-1) and other urinary biomarkers using the MILLIPLEX MAP Rat Kidney Panel. Vancomycin in plasma was quantified via LC-MS/MS. PK analyses were conducted using Pmetrics for R. PK exposures during the first 24 hours (i.e., AUC_0-24hours, CMAX_0-24hours) were calculated from Bayesian posteriors. Pharmacokinetic-toxicodynamic (PK-TD) relationships were assessed with the best fit mathematic model (e.g., exposure-response curve fitting in GraphPad v.7).

Results

Sixty-four vancomycin treated and control rats contributed to PK-TD data. An exposure-response (via 4-parameter Hill) model was identified for AUC_0-24hoursvs KIM-1 (R² = 0.62, Figure 1a). Convergence was not obtained for exposure-response models for CMAX_0-24hours and CMIN, which was also verified visually (Figure 1b and c). Despite the intensive fractionation, AUC_0-24hoursand CMAX_0-24hours were highly correlated (P < 0.001, rho = 0.89) and this correlation was consistent across KIM-1 values (Figure 2).

Conclusion

Vancomycin-induced kidney injury was driven by AUC_{0-24 hours} and not CMIN. Continuous infusion studies are needed to understand if changing the infusion profile can improve safety; however, these studies suggest that isometric AUCs may result in similar toxicity. When using intermittent infusion schemes, clinicians should focus on AUC to prevent AKI.

Disclosures

All authors: No reported disclosures.

Measuring the impact of varying denominator definitions on standardized antibiotic consumption rates: implications for antimicrobial stewardship programmes

Objectives

To quantify the impact of varying the at-risk days definition on the overall report of at-risk days and on the calculated standardized consumption rates (SCRs) for piperacillin/tazobactam, amikacin, daptomycin and vancomycin.

Methods

Data were evaluated for two system hospitals, an 894 bed academic centre and a 114 bed community hospital. Aggregate inpatient antibiotic administration and occupancy data were extracted from electronic databases at the facility-wide level. Occupancy data were reported from admission-discharge-transfer systems. At-risk days were defined as hospital days present (DP), patient days (PD), persons present (PP) and billing days (BD). Inpatient antimicrobial days of therapy (DOT) across four major antimicrobial agents were used to calculate facility-wide SCRs using each denominator and were evaluated by least-squares regression and R2 values.

Results

Within the 894 bed academic hospital, the average monthly facility-wide days were 28 424, 22 198, 15 957 and 14 789 by the DP, PP, PD and BD definitions, respectively. Within the 114 bed community hospital, the average monthly facility-wide days were 5175, 3523 and 2816 by the DP, PP and PD definitions, respectively. Strong concordance was observed between facility-wide SCRs using the DP and PP definitions in both the academic (R2 = 0.99, y = 0.78x - 0.001) and community (R2 = 0.99, y = 0.68x - 0.03) centres across all four inpatient antibiotics evaluated. In an analysis of piperacillin/tazobactam SCRs, rates were over-predicted by 28%-93% at the facility-wide level across centres using alternative denominators.

Conclusions

We found that data source and definitions of at-risk denominator days meaningfully impact antibiotic SCRs. Centres should carefully consider these potential sources of variation when setting consumption benchmarks and internally evaluating use.

Polymyxin B Pharmacokinetics in Adult Cystic Fibrosis Patients

OBJECTIVES

Polymyxin B pharmacokinetics (PK) in adults with cystic fibrosis (CF) are not well described. The goals of this pilot study were to identify a PK model for patients with CF receiving polymyxin B with exploration of covariate relationships of the PK parameters, to compare polymyxin B PK parameters in adults without CF, and to probe exposures associated with different dosing schemes through simulation.

METHODS

Adult patients with CF treated with polymyxin B at New York-Presbyterian Hospital had PK samples measured by liquid chromatography-mass spectrometry (MS)/MS. Multiple PK models were fit utilizing Pmetrics for R. Model covariates considered included: age, total body weight, creatinine clearance, albumin, and body mass index. PK parameters in CF patients were compared with PK parameters for 53 adults without CF who were receiving polymyxin B from the same institution. Simulations with target exposure (area under the curve)/minimum inhibitory concentration (MIC) of 20 mg*L/h were conducted for different dosing schemes and MIC ranges.

MAIN RESULTS

Nine patients with CF received between 58 and 240 mg of polymyxin B (median 1.47 mg/kg/dose [IQR (1.43-1.65)]). A two-compartment model adjusting polymyxin B clearance for patient CrCl was better than a standard two-compartment model (p=0.004) in CF patients. When compared to PK parameters for patients without CF, PK parameters of polymyxin B in CF were similar (p>0.05). Simulations for plasma concentrations showed all regimens performed adequately at MICs between 0.03125 and 0.125 mg/L but not at increasing MICs of 1 and 2 mg/L.

CONCLUSIONS

In this pilot study of polymyxin B PK in adults with CF, the PK parameters of polymyxin B were mostly similar to adults without CF. We observed a potential association between CrCl and polymyxin B clearance, which stands in contrast to the general adult population. However, this observation requires further study. Additional studies focusing on optimal and safe polymyxin B dosing in CF are needed.