Cefepime pharmacokinetics in critically ill children and young adults undergoing continuous kidney replacement therapy.

OBJECTIVES: Cefepime is an antibiotic commonly used to treat sepsis and is cleared by renal excretion. Cefepime dosing requires adjustment in patients with decreased kidney function and in those receiving continuous kidney replacement therapy (CKRT). We aimed to characterize cefepime PK in a diverse cohort of critically ill paediatric patients on CKRT. METHODS: Patients were identified from an ongoing pharmacokinetic/pharmacodynamic (PK/PD) study of beta-lactam antibiotics, and were included if they had received at least two cefepime doses in the ICU and were on CKRT for at least 24 h. PK parameters were estimated using MwPharm++ with Bayesian estimation and a paediatric population PK model. Target attainment was assessed as time of free cefepime concentrations above minimum inhibitory concentration (fT > 1× or 4 × MIC). RESULTS: Seven patients were included in the study (ages 2 to 20 years). CKRT indications included liver failure (n = 1), renal failure (n = 4) and fluid overload (n = 2). Total effluent flow rates ranged from 1833 to 3115 (mean 2603) mL/1.73 m2/h, while clearance was 2.11-3.70 (mean 3.0) L/h/70 kg. Effluent flows were lower, but clearance and fT > MIC were similar to paediatric data published previously. Using Pseudomonas aeruginosa MIC breakpoints, all patients had 100% of dosing interval above MIC, but only one had 100% of dosing interval above 4× MIC. CONCLUSIONS: Since most patients failed to attain stringent targets of 100% fT > 4×  MIC, model-informed precision dosing may benefit such patients.

Evidence of a clinically significant drug-drug interaction between cannabidiol and tacrolimus.

Cannabidiol (CBD), a major purified nonpsychoactive component of cannabis with anticonvulsant properties, was approved by the U.S. Food and Drug Administration (FDA) in June 2018 as an adjuvant treatment for refractory epilepsy (Epidiolex; GW Pharmaceuticals). CBD is metabolized by cytochrome P450 (CYP)3A4 and CYP2C19 with a growing body of evidence suggesting it is also a potent inhibitor of these pathways. We report for the first time a significant drug-drug interaction between the purified CBD product and tacrolimus. A participant in a CBD clinical trial for epilepsy who was also receiving tacrolimus showed an approximately 3-fold increase in dose-normalized tacrolimus concentrations while receiving 2000-2900 mg/day of CBD. Our report delineates an important concern for the transplant community with the increasing legalization of cannabis and advent of an FDA-approved CBD product. Larger studies are needed to better understand the impact of this drug-drug interaction in solid organ transplant recipients.

Pharmacokinetics of glycerol phenylbutyrate in pediatric patients 2 months to 2 years of age with urea cycle disorders.

INTRODUCTION: Glycerol phenylbutyrate (GPB) is approved in the US and EU for the chronic management of patients ≥2 months of age with urea cycle disorders (UCDs) who cannot be managed by dietary protein restriction and/or amino acid supplementation alone. GPB is a pre-prodrug, hydrolyzed by lipases to phenylbutyric acid (PBA) that upon absorption is beta-oxidized to the active nitrogen scavenger phenylacetic acid (PAA), which is conjugated to glutamine (PAGN) and excreted as urinary PAGN (UPAGN). Pharmacokinetics (PK) of GPB were examined to see if hydrolysis is impaired in very young patients who may lack lipase activity. METHODS: Patients 2 months to <2 years of age with UCDs from two open label studies (n = 17, median age 10 months) predominantly on stable doses of nitrogen scavengers (n = 14) were switched to GPB. Primary assessments included traditional plasma PK analyses of PBA, PAA, and PAGN, using noncompartmental methods with WinNonlin™. UPAGN was collected periodically throughout the study up to 12 months. RESULTS: PBA, PAA and PAGN rapidly appeared in plasma after GPB dosing, demonstrating evidence of GPB cleavage with subsequent PBA absorption. Median concentrations of PBA, PAA and PAGN did not increase over time and were similar to or lower than the values observed in older UCD patients. The median PAA/PAGN ratio was well below one over time, demonstrating that conjugation of PAA with glutamine to form PAGN did not reach saturation. Covariate analyses indicated that age did not influence the PK parameters, with body surface area (BSA) being the most significant covariate, reinforcing current BSA based dosing recommendations as seen in older patients. CONCLUSION: These observations demonstrate that UCD patients aged 2 months to <2 years have sufficient lipase activity to adequately convert the pre-prodrug GPB to PBA. PBA is then converted to its active moiety (PAA) providing successful nitrogen scavenging even in very young children.

Pharmacokinetics of meropenem in children receiving continuous renal replacement therapy: Validation of clinical trial simulations.

Meropenem is frequently prescribed in critically ill children receiving continuous renal replacement therapy (CRRT). We previously used clinical trial simulations to evaluate dosing regimens of meropenem in this population and reported that a dose of 20 mg/kg every 12 hours optimizes target attainment. Meropenem pharmacokinetics were investigated in this prospective, open-label study to validate our previous in silico predictions. Seven patients received meropenem (13.8-22 mg/kg) administered intravenously every 12 hours as part of standard care. A mean dose of 18.6 mg/kg of meropenem was administered, resulting in a mean peak concentration of 80.1 µg/mL. Meropenem volume of distribution was 0.35 ± 0.085 L/kg. CRRT clearance was 40.2 ± 6.6 mL/(min · 1.73 m(2) ) and accounted for 63.4% of the total clearance of 74.8 ± 36.9 mL/(min · 1.73 m(2) ). Simulations demonstrated that a dose of 20 mg/kg every 12 hours resulted in a time above the minimum inhibitory concentration (%fT > MIC) of 100% in 5 out of 7 subjects, with a %fT > MIC of 93% and 43% in the remaining 2 subjects. We conclude that CRRT contributed significantly to the total clearance of meropenem. A dosing regimen of 20 mg/kg achieved good target attainment in critically ill children receiving CRRT, which is consistent with our previously published in silico predictions.

Safety and Dose Escalation Study of Intravenous Zinc Supplementation in Pediatric Critical Illness.

BACKGROUND: Critically ill children have low plasma zinc (pZn), correlating with organ failure. Since Zn influences inflammation, immune function, and glucose control, Zn supplementation is a plausible therapeutic modality. We sought to determine a safe dose of intravenous (IV) Zn to restore pZn in critically ill children. METHODS: Stepwise dose escalation study of IV Zn supplementation at a tertiary children's hospital. All children (<10 years) admitted to the pediatric intensive care unit with a Pediatric Risk of Mortality III score >5, or ≥1 new organ failure were eligible. After consent, patients were sequentially enrolled into 4 dosing groups: (1) no zinc, (2) Zn250: 250 mcg/kg/d ZnSO4, (3) Zn500: 500 mcg/kg/d ZnSO4, or (4) Zn750: 750 mcg/kg/d ZnSO4 ZnSO4 was administered 3 times daily for 7 days. pZn was measured at baseline, end of first ZnSO4 infusion, 1 hour postinfusion, and 7 hours postinfusion on day 1, then daily through days 2-7. Interleukin-6 (IL-6), C-reactive protein (CRP), and lymphocyte subsets were measured on days 1 and 3. Glucose was measured 3 times daily for 7 days. RESULTS: Twenty-four patients were enrolled. Baseline demographics were similar among groups. Baseline pZn was low in all patients (mean [SD], 41.8 [16.0] mcg/dL). pZn increased over the study period in supplemented groups; however, mean pZn in the Zn750 group exceeded the 50th percentile. pZn was not associated with IL-6, CRP, or lymphocyte subsets among groups. Degree of hyperglycemia did not differ among groups. No patient had a study-related adverse event. CONCLUSIONS: IV zinc supplementation at 500 mcg/kg/d restores pZn to near the 50th percentile and is well tolerated.

Meropenem in children receiving continuous renal replacement therapy: clinical trial simulations using realistic covariates.

Meropenem is frequently prescribed in children receiving continuous renal replacement therapy (CRRT). Fluid overload is often present in critically ill children and affects drug disposition. The purpose of this study was to develop a pharmacokinetic model to (1) evaluate target attainment of meropenem dosing regimens against P. aeruginosa in children receiving CRRT and (2) estimate the effect of fluid overload on target attainment. Clinical trial simulations were employed to evaluate target attainment of meropenem in various age groups and degrees of fluid overload in children receiving CRRT. Pharmacokinetic parameters were extracted from published literature, and 287 patients from the prospective pediatric CRRT registry database provided realistic clinical covariates including patient weight, fluid overload, and CRRT prescription characteristics. Target attainment at 40% and 75% time above the minimum inhibitory concentration was evaluated. Clinical trial simulations demonstrated that children greater than 5 years of age achieved acceptable target attainment with a dosing regimen of 20 mg/kg every 12 hours. In children less than 5, however, increased dosing of 20 mg/kg every 8 hours was needed to optimize target attainment. Fluid overload did not affect target attainment. These in silico model predictions will need to be verified in vivo in children receiving meropenem and CRRT.

Continuous infusion of beta-lactams.

PURPOSE OF REVIEW: Continuous infusion of beta-lactam antibiotics is becoming increasingly popular. The background and current clinical evidence are discussed. Tools to apply continuous infusion are analyzed. RECENT FINDINGS: One randomized controlled trial in an ICU setting and two nonrandomized controlled trials have shown continuous infusion to be more beneficial than intermittent infusion. One randomized controlled trial in chronic obstructive pulmonary disorder patients, however, showed no difference between the two treatments. The stability of most beta-lactams for use during continuous infusion has been documented. SUMMARY: Killing of bacteria by beta-lactam antibiotics is maximal at around four times the minimum inhibitory concentration in vitro. To ensure an optimal effect when treating severe infections, free unbound concentrations at or above four times the minimum inhibitory concentration should be maintained. Although continuous infusion has been demonstrated to be superior in animal studies, randomized clinical trials have failed to confirm this in humans, primarily because of suboptimal design. A better designed randomized clinical trial, set up as a pilot study, recently demonstrated a favorable outcome with continuous infusion. A major issue during continuous infusion is the stability of the antibiotic, which may limit its application. The calculation of the infusion rate necessary to obtain the desired free drug concentration is relatively straightforward.

A retrospective analysis using Monte Carlo simulation to evaluate recommended ceftazidime dosing regimens in healthy volunteers, patients with cystic fibrosis, and patients in the intensive care unit.

BACKGROUND: Over the past decades, the relationship between the pharmacokinetic (PK) properties of antibiotics, MICs, and clinical effects has been increasingly well understood. Interpatient variability in the PK profile, however, has only recently been recognized as a major factor in predicting the outcome in individual patients and establishing breakpoints for clinical susceptibility. Most predictions to date have used data from healthy volunteers. OBJECTIVE: The purpose of this study was to perform Monte Carlo simulations of the PK/pharmacodynamic relationships of ceftazidime to assess whether the probability of target attainment (PTA) differed significantly between 3 distinct populations. To that end, population PK models of ceftazidime were developed for the 3 populations. METHODS: Serum concentration-time data from earlier studies in healthy volunteers (n = 8), patients with cystic fibrosis (CF) (n = 17), and patients in the intensive care unit (ICU) (n = 6) were used to obtain population PK parameter estimates and covariance matrices using the nonparametric adaptive grid program. The PTA for each group was obtained using 10,000 patient simulations for dosing regimens of 1000 and 2000 mg q8h over a range of MICs and percentages of time that concentrations of unbound drug remained above the MIC (%T > MIC). RESULTS: The relationship between the MIC and the population mean %T > MIC, as well as the PTA profiles, differed markedly between the 3 groups as a result of both differences and variations in V(d) and Cl. Breakpoints based on a 100% PTA for a %T > MIC of 60% were < or = 4, 0.5, and 0.5 mg/L in healthy volunteers, patients with CF, and patients in the ICU, respectively. However, when PTA values between 90% and 100% were reevaluated and differences in clinical dosing regimens were accounted for, the resulting breakpoints were identical in the 3 groups. CONCLUSIONS: PK parameter estimates for ceftazidime based on data from a small group of healthy volunteers resulted in a clinical susceptibility breakpoint comparable to those for patients with CF and patients in the ICU. Based on the study findings, this breakpoint would be < or = 4 mg/L. Patients suspected of having unusually high rates of clearance should be monitored closely.