Population Pharmacokinetics and Pharmacodynamic Implementation of Meropenem in Critically Ill Pediatric Patients

This study investigates the optimal meropenem (MEM) dosing regimen for critically ill pediatric patients, for which there is a lack of pharmacokinetic (PK) studies. We conducted a retrospective single-center PK and pharmacodynamic (PD) analysis of 34 pediatric intensive care unit patients who received MEM. Individual PK parameters were determined by a two-compartment analysis. The median (range) age and body weight were 1.4 (0.03–14.6) years old and 8.9 (2.7–40.9) kg, respectively, and eight (23.5%) patients received continuous renal replacement therapy (CRRT), of which three received extracorporeal membrane oxygenation. Renal function, systemic inflammatory response syndrome (SIRS) score, and the use of CRRT for central volumes of distribution (Vc) were identified as significant covariates. The mean clearance (CL), Vc, and peripheral volume of distribution (Vp) were 0.45 l/kg/h, 0.49 l/kg, and 0.34 l/kg, respectively. The mean population CL of MEM increased by 35% in patients with SIRS and Vc increased by 66% in patients on CRRT in the final model. Dosing simulations suggested that the standard dosing regimen provided insufficient PD exposures of 100% free time above the minimum inhibitory concentration, and higher doses (40–80 mg/kg/dose every 8 h) with a prolonged 3-h infusion were required to ensure the appropriate PD exposures for patients with SIRS. Our PK model indicated that critically ill pediatric patients are at risk of subtherapeutic exposure under the standard dosing regimen of MEM. A larger, prospective investigation confirming the safety and efficacy of higher concentrations and prolonged infusion of MEM is necessary.

Population Pharmacokinetic Analysis of Emapalumab, a Fully Human, Anti-Interferon Gamma Monoclonal Antibody, in Children with Primary Hemophagocytic Lymphohistiocytosis

Introduction: Primary hemophagocytic lymphohistiocytosis (HLH) is a rare syndrome characterized by pathologic immune activation and hyperinflammation. It typically manifests during infancy and is invariably fatal if untreated. Interferon gamma (IFNy) is considered a key contributor to the hyperinflammation of HLH. Thus, neutralization of IFNy could help control the disease until haematopoietic stem cell transplantation, the only curative treatment. Emapalumab, a fully human, anti-IFNy monoclonal antibody, binds to and neutralizes IFNy. Emapalumab is the first and only approved (FDA) treatment for primary HLH. It is indicated for the treatment of adult and pediatric patients with HLH with refractory, recurrent, or progressive disease, or intolerance to conventional HLH therapy. Objective: To develop a population pharmacokinetic (PK) model to describe the PK profile of emapalumab. Methods: PK data were obtained from patients with primary HLH administered emapalumab intravenously during an open-label, single-group, phase 2/3 clinical trial (NCT01818492) and as part of a compassionate use program. A population PK analysis was performed using nonlinear mixed effects modeling (NONMEM® version 7.3.0). Predictive performance of the model was assessed using a visual predictive check. Results: The PK of emapalumab was adequately described by a two-compartment model. All model parameters were estimated with good precision. Central and peripheral volumes of distribution were 0.059 and 0.079 L/kg, respectively. Exploratory graphical analysis showed that (i) IFNy production varied significantly between and within patients as a function of time; (ii) the higher the IFNy production, the faster the elimination of emapalumab due to target-mediated drug disposition; and (iii) the higher the IFNy production, the higher the dose of emapalumab required to reach the neutralizing concentration of IFNy (evidenced by a higher target-mediated clearance of emapalumab). Of the parameters examined, only body weight and total IFNy (free and bound) levels were found to significantly influence the PK of emapalumab. The allometric exponents of body weight for the volume of distribution and clearance were 1 (fixed) and 0.886 (95% confidence interval 0.68, 1.09), respectively. These values support the bodyweight-based dosing of emapalumab (i.e. mg/kg). At values of total IFNy from 103 to 106 pg/mL, the total clearance (linear + target mediated) of emapalumab ranged from 0.0012 to 0.0140 L/h for a bodyweight of 5 kg, with corresponding terminal half-lives from 17.5 to 2.3 days. This wide variance in clearances and half-lives partly explains the emapalumab dose adaptations that are required for treating primary HLH patients. Conclusion: The population PK model reliably predicted serum concentrations of emapalumab in patients with primary HLH. The central and peripheral volumes of distribution were low, clearance was slow, and the terminal half-life long. The expected dynamic of the biology of IFNy was confirmed and included in the population PK model. Simulations using this model supported the proposed dosing scheme of emapalumab in patients with primary HLH. Disclosures Laveille: Sobi: Consultancy. Jacqmin:Sobi: Consultancy. de Min:Sobi: Consultancy.

Pharmacologic Considerations for the Obese Patient

Obese patients gain lean and mass in different proportions to total body mass. This results in different volumes of distribution (Vd) for medications according to their lipid solubility compared to that of normal weight patients. High body mass index (BMI) patients are at increased risk of medical comorbidities that may affect drug metabolism and clearance. Anesthesiologists should factor in these differences in order to prevent erroneous medication dosing. This review contains 1 figure, 1 table, and 61 references. Keywords: obesity, induction agents, analgesics, inhaled anesthetics, neuromuscular blocking agents, reversal agents, local anesthetics, pharmacology, pharmacokinetics, pharmacodynamics

Comparable Bioavailability and Disposition of Pefloxacin in Patients with Cystic Fibrosis and Healthy Volunteers Assessed via Population Pharmacokinetics

Quinolone antibiotics present an attractive oral treatment option in patients with cystic fibrosis (CF). Prior studies have reported comparable clearances and volumes of distribution in patients with CF and healthy volunteers for primarily renally cleared quinolones. We aimed to provide the first pharmacokinetic comparison for pefloxacin as a predominantly nonrenally cleared quinolone and its two metabolites between both subject groups. Eight patients with CF (fat-free mass [FFM]: 36.3 ± 6.9 kg, average ± SD) and ten healthy volunteers (FFM: 51.7 ± 9.9 kg) received 400 mg pefloxacin as a 30 min intravenous infusion and orally in a randomized, two-way crossover study. All plasma and urine data were simultaneously modelled. Bioavailability was complete in both subject groups. Pefloxacin excretion into urine was approximately 74% higher in patients with CF compared to that in healthy volunteers, whereas the urinary excretion of metabolites was only slightly higher in patients with CF. After accounting for body size and composition via allometric scaling by FFM, pharmacokinetic parameter estimates in patients with CF divided by those in healthy volunteers were 0.912 for total clearance, 0.861 for nonrenal clearance, 1.53 for renal clearance, and 0.916 for volume of distribution. Nonrenal clearance accounted for approximately 90% of total pefloxacin clearance. Overall, bioavailability and disposition were comparable between both subject groups.

Clinical Pharmacology of Antibiotics

Antimicrobial pharmacology and its effect on prescribing is quite complex. Selecting an antibiotic that will optimally treat an infection while minimizing adverse effects and the development of resistance is only the first step, as one must also consider the patient’s individual pharmacokinetic alterations and the pharmacodynamic properties of the drug when prescribing it as well. Patients with CKD may have alterations in their protein binding, volumes of distribution, kidney clearance, and nonrenal clearance that necessitates antibiotic dose adjustments to prevent the development of toxicity. Knowledge of a drug’s pharmacodynamics, defined as the relationship between drug exposure and antibacterial efficacy, provides some guidance regarding the optimal way to make dose adjustments. Different pharmacodynamic goals, such as maximizing the time that free (unbound) drug concentrations spend above the minimum inhibitory concentration (MIC) for time dependent drugs (e.g., β-lactams) or maximizing the free peak-to-MIC ratio for concentration-dependent antibiotics (e.g., aminoglycosides), require different adjustment strategies; for instance, decreasing the dose while maintaining normal dosing frequency or giving normal (or even larger) doses less frequently, respectively. Patients receiving hemodialysis have other important prescribing considerations as well. The nephrologist or patient may prefer to receive antibiotics that can be administered intravenously toward the end of a dialysis session. Additionally, newer dialysis technologies and filters can increase drug removal more than originally reported. This review will discuss the place in therapy, mechanism of action, pharmacokinetic, pharmacodynamic, and other pharmacologic considerations encountered when prescribing commonly used antibiotics in patients with chronic kidney disease or ESKD.

Differential Molecular Modeling Predictions of Mid and Conventional Dialysate Flows

Background: High dialysate flow rates (QD) of 500–800 mL/min are used to maximize urea removal during conventional hemodialysis. There are few data describing hemodialysis with use of mid-rate QD (300 mL/min). Methods: We constructed uremic solute (urea, beta2-microglobulin and phosphate) kinetic models at varying volumes of distribution and blood flow rates to predict solute clearances at QD of 300 and 500 mL/min. Results: Across a range of volumes of distribution a QD of 300 mL/min generally yields a predicted urea spKt/V greater than 1.2 during typical treatment times with a small difference in urea spKt/V between a QD of 300 and 500 mL/min. A larger urea KoA dialyzer and 15 min of additional time narrows the urea spKt/V difference. No substantial differences were observed regarding the kinetics of beta2-microglobulin and phosphate for QD of 300 vs. 500 mL/min. Conclusion: A QD of 300 mL/min can achieve urea clearance targets. Hemodialysis systems using mid-rate QD can be expected to provide adequate hemodialysis, as currently defined.

Pharmacodynamics of Cefepime Combined with Tazobactam against Clinically Relevant Enterobacteriaceae in a Neutropenic Mouse Thigh Model

ABSTRACT The lack of new antibiotics has prompted investigation of the combination of two existing agents—cefepime, a broad-spectrum cephalosporin, and tazobactam—to broaden their efficacy against extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae. We determined the pharmacokinetic (PK) and pharmacodynamic (PD) properties of the combination in a murine neutropenic thigh model in order to establish its exposure-response relationships (ERRs). The PK of cefepime were determined for five doses; that of tazobactam was determined in earlier studies (Melchers et al., Antimicrob Agents Chemother 59:3373–3376, 2015, https://doi.org/10.1128/AAC.04402-14 ). The PK were linear for both compounds. The estimated mean (standard deviation [SD]) half-life of cefepime was 0.33 (0.12) h, and that of tazobactam was 0.176 (0.026) h; the volumes of distribution (V) were 0.73 liters/kg and 1.14 liters/kg, respectively. PD studies of cefepime administered every 2 h (q2h) with or without tazobactam, including dose fractionation studies of tazobactam, were performed against six ESBL-producing isolates. A sigmoidal maximum-effect (E max) model was fitted to the data. In the dose fractionation study, the q2h regimen was more efficacious than the q4h and q6h regimens, indicating time-dependent activity of tazobactam. The threshold concentration (CT ) best correlating with tazobactam efficacy was 0.25 mg/liter, as evidenced by the best fit of the percentage of time above the threshold concentration (%fT>CT ) and response. A mean %fT>CT of 24.6% (range, 11.4 to 36.3%) for a CT of 0.25 mg/liter was required to obtain a bacteriostatic effect. We conclude that tazobactam enhanced the effect of cefepime in otherwise resistant isolates of Enterobacteriaceae and that the %fT>CT of 0.25 mg/liter best correlated with efficacy. These studies provide the basis for the development of human dosing regimens for this combination.

Pharmacokinetics of Peramivir in an Adolescent Patient Receiving Continuous Venovenous Hemodiafiltration

Critically ill patients requiring renal replacement therapy commonly experience pharmacokinetic alterations. This case report describes the pharmacokinetics of peramivir (Rapivab, BioCryst Pharmaceuticals, Inc, Durham, NC), the first US Food and Drug Administration–approved intravenous neuraminidase inhibitor for the treatment of influenza, in an adolescent patient receiving continuous renal replacement therapy (CRRT). A 49.5-kg, 17-year-old Caucasian female presented with fever, cough, and persistent hypoxia. She quickly progressed to acute respiratory and renal failure in the setting of viral septic shock as a result of a severe influenza H1N1 infection. On hospital day 3, therapy was switched from oseltamivir (Tamiflu, Roche Laboratories Inc, Nutley, NJ) to peramivir owing to the concern for inadequate enteral absorption. On the third day of peramivir treatment, at a dose of 200 mg daily, peramivir serum concentrations revealed a smaller peak concentration, larger volumes of distribution, similar 24-hour area under the curve, and a shorter half-life as compared to adult patients with normal renal function. This illustrated the significant differences in pharmacokinetics when administered in the setting of CRRT. The patient had resolution of viral infection as evidenced by negative respiratory viral panel polymerase chain reaction at hospital day 14 and was eventually discharged at her baseline.