Significant Covariates For Clearance Research Articles

Population pharmacokinetics of voriconazole and the role of CYP2C19 genotype on treatment optimization in pediatric patients.

The aim of this study was to evaluate factors that impact on voriconazole (VRC) population pharmacokinetic (PPK) parameters and explore the optimal dosing regimen for different CYP2C19 genotypes in Chinese paediatric patients. PPK analysis was used to identify the factors contributing to the variability in VRC plasma trough concentrations. A total of 210 VRC trough concentrations from 91 paediatric patients were included in the study. The median VRC trough concentration was 1.23 mg/L (range, 0.02 to 8.58 mg/L). At the measurement of all the trough concentrations, the target range (1.0~5.5 mg/L) was achieved in 52.9% of the patients, while subtherapeutic and supratherapeutic concentrations were obtained in 40.9% and 6.2% of patients, respectively. VRC trough concentrations were adjusted for dose (Ctrough/D), with normal metabolizers (NMs) and intermediate metabolizers (IMs) having significantly lower levels than poor metabolizers (PMs) (PN-P < 0.001, PI-P = 0.039). A one-compartment model with first-order absorption and elimination was suitable to describe the VRC pharmacokinetic characteristics. The final model of VRC PPK analysis contained CYP2C19 phenotype as a significant covariate for clearance. Dose simulations suggested that a maintenance dose of 9 mg/kg orally or 8 mg/kg intravenously twice daily was appropriate for NMs to achieve the target concentration. A maintenance dose of 9 mg/kg orally or 5 mg/kg intravenously twice daily was appropriate for IMs. Meanwhile, PMs could use lower maintenance dose and an oral dose of 6 mg/kg twice daily or an intravenous dose of 5mg/kg twice daily was appropriate. To increase the probability of achieving the therapeutic range and improving efficacy, CYP2C19 phenotype can be used to predict VRC trough concentrations and guide dose adjustments in Chinese pediatric patients.

Development of a population pharmacokinetic model to characterize the pharmacokinetics of intrathecally administered tominersen in cerebrospinal fluid and plasma.

Tominersen is an intrathecally administered antisense oligonucleotide targeting huntingtin mRNA which leads to a dose-dependent, reversible lowering of cerebrospinal fluid (CSF) mutant huntingtin protein concentration in individuals with Huntington's disease. Nonlinear mixed-effect population pharmacokinetic (PopPK) modeling was conducted to characterize the CSF and plasma pharmacokinetics (PK) of tominersen, and to identify and quantify the covariates that affect tominersen PKs. A total of 750 participants from five clinical studies with a dose range from 10 to 120 mg contributed CSF (n = 6302) and plasma (n = 5454) PK samples. CSF PK was adequately described by a three-compartment model with first-order transfer from CSF to plasma. Plasma PK was adequately described by a three-compartment model with first-order elimination from plasma. Baseline total CSF protein, age, and antidrug antibodies (ADAs) were the significant covariates for CSF clearance. Body weight was a significant covariate for clearances and volumes in plasma. ADAs and sex were significant covariates for plasma clearance. The developed PopPK model was able to describe tominersen PK in plasma and CSF after intrathecal administration across a range of dose levels, and relevant covariate relationships were identified. This model has been applied to guide dose selection for future clinical trials of tominersen in patients with Huntington's disease.

Population Pharmacokinetic Analysis of Perampanel in Portuguese Patients Diagnosed with Refractory Epilepsy.

Perampanel is a promising antiepileptic drug (AED) for refractory epilepsy treatment due to its innovative mechanism of action. This study aimed to develop a population pharmacokinetic (PopPK) model to be further used in initial dose optimization of perampanel in patients diagnosed with refractory epilepsy. A total of seventy-two plasma concentrations of perampanel obtained from forty-four patients were analyzed through a population pharmacokinetic approach by means of nonlinear mixed effects modeling (NONMEM). A one-compartment model with first-order elimination best described the pharmacokinetic profiles of perampanel. Interpatient variability (IPV) was entered on clearance (CL), while the residual error (RE) was modeled as proportional. The presence of enzyme-inducing AEDs (EIAEDs) and body mass index (BMI) were found as significant covariates for CL and volume of distribution (V), respectively. The mean (relative standard error) estimates for CL and V of the final model were 0.419 L/h (5.56%) and 29.50 (6.41%), respectively. IPV was 30.84% and the proportional RE was 6.44%. Internal validation demonstrated an acceptable predictive performance of the final model. A reliable population pharmacokinetic model was successfully developed, and it is the first enrolling real-life adults diagnosed with refractory epilepsy.

Comparative pharmacokinetics of valproic acid among Pakistani and South Korean patients: A population pharmacokinetic study

PurposeThe pharmacokinetics of valproic acid have been evaluated in a variety of populations however, the comparison in two different populations was yet to be reported. This study is aimed to compare the pharmacokinetics of valproic acid in Pakistani and South Korean patients.MethodThe therapeutic drug monitoring (TDM) data of valproic acid from 92 Pakistani patients with 218 samples was combined with the data of 99 South Korean patients with 335 samples in order to form a pooled dataset of 191 patients with 553 samples. Population pharmacokinetic model was developed on NONMEM® software by using first order conditional estimation method for estimation of pharmacokinetic parameters. The influence of different covariates including ethnicity was evaluated the stepwise covariate modelling. The final model was evaluated for predictive performance and robustness by using goodness of fit plots and bootstrap analysis respectively.ResultsThe data was better described by one compartment model with first order elimination. The value for clearance (CL) of valproic in pooled data was 0.931 L/h with 43.4% interindividual variability (IIV) while volume of distribution (Vd) was 16.6 L with 22.3% IIV. In covariate analysis, ethnicity and body weight were significant covariates for CL while body weight was also significant for Vd.ConclusionA significant difference in CL of valproic acid among Pakistani and South Korean patients was observed. The model can be used for the dose tailoring of valproic acid based on ethnicity and body weight of Pakistani and South Korean patients.

Population pharmacokinetics of omeprazole in obese and normal-weight adults

ABSTRACT Background Obesity is related to many pathophysiological changes that may result in altered drug disposition. Omeprazole is the most common option utilized for acid-related disorders ; however, the pharmacokinetic (PK) and dosing recommendations for the obese patient population are lacking. Methods Data from 40 healthy subjects with normal weights and data from 61 obese subjects were included. The subjects all received a single dose of 20 mg of omeprazole. Nonlinear mixed effects modeling were performed to characterize the effect of obesity on omeprazole PK. Results A one-compartment model with twelve transit absorption compartments and linear elimination described the data best. A lower clearance was observed in the obese patient population than in the normal-weight subjects. Moreover, the CYP2C19 genotype was identified as a significant covariate for clearance. Conclusion Given the potential adverse events related to high exposure to proton pump inhibitors over time, obese patients may require a lower dose of omeprazole for long-term treatment. Further studies in obese individuals into other drugs metabolized by CYP2C19 are warranted, especially those with a narrow therapeutic window. Clinical Trial Registration www.chictr.org.cn identifier is ChiCTR2100046578; www.chinadrugtrials.org.cn identifier is CTR20190175.

Influence of blood group and von Willebrand factor on population pharmacokinetics and dose individualization of recombinant factor VIII in Taiwanese patients with haemophilia A.

The large interpatient variability in the pharmacokinetic (PK) parameters of recombinant Factor VIII (rFVIII) observed in haemophilia A hinders efficient and cost-beneficial prophylactic regimen initiation. Identification of factors influencing the PK of rFVIII may shed more light on personalised treatment. This study aimed to develop a population PK model in the Taiwanese haemophilia A and evaluate the current national health insurance (NHI) reimbursement guidelines of Taiwan for haemophilia treatment. A population PK analysis was established based on 69 Taiwanese with moderate or severe haemophilia A. A nonlinear mixed-effects modelling (NONMEM® ) was used to estimate PK parameters and their variabilities. A Monte Carlo simulation was performed to evaluate different prophylactic regimens. A two-compartment model with first-order elimination best described the rFVIII data. Weight-based allometric scaling was related to clearance and central volume of distribution. Blood type and baseline von Willebrand factor (VWF) were significant covariates for clearance. For single dose simulations, a time achieving target level (>1IU/dL) was associated with increasing rFVIII dose and VWF level. The multiple dose simulations showed that>96.4% of patients with high VWF level (>200%) had predicted trough level>1IU/dL for all dosing regimens (15-40IU/kg, two to three times weekly). However, for twice weekly dosing, lower percentage (47.62-62.20%) of patients with blood group O and low VWF level (<50%) achieved a predicted trough level>1IU/dL. The population PK of rFVIII was successfully developed. Dose adjustment based on blood type and VWF level should be considered.

Population pharmacokinetics of ciclosporin in allogeneic hematopoietic stem cell transplant recipients: C-reactive protein as a novel covariate for clearance.

Ciclosporin (CsA), a potent immunosuppressive agent used to prevent graft-versus-host disease in allogeneic hematopoietic stem cell transplant (allo-HSCT) recipients, is characterized by large inter-individual variability and a narrow therapeutic range. The aim of this study was to develop a population pharmacokinetic model for CsA in Chinese allo-HSCT recipients and to identify covariates influencing CsA pharmacokinetics. A total of 758 retrospective drug monitoring data points were collected after intravenous infusion or oral administration of CsA from 59 patients. Population pharmacokinetic analysis was performed using nonlinear mixed effects modelling expressed by differential equations. Monte Carlo simulation was applied to optimize dosage regimens. The final model was validated using bootstrap and normalized prediction distribution errors. The results showed that the daily CsA dose, haematocrit, total bile acid, C-reactive protein (CRP) and co-administration of triazole antifungal agent were identified as significant covariates for clearance (CL) of CsA. The typical value of CL was 19.8L/h with an inter-individual variability of 13.1%. The volume of distribution was 1340L. Bioavailability was 67.2% with an inter-individual variability of 8.5%. Dosing simulation based on the developed model indicated that patients with high CRP concentration required a higher daily dose to attain the therapeutic trough concentration. The influence of CRP ultimately on the therapy outcome of CsA is not clear, which needs further study. CRP concentration was identified as a novel marker associated with CsA pharmacokinetics, which should be considered when determining the appropriate dosage of CsA in allo-HSCT recipients.

Development of a new pharmacokinetic model for target-concentration controlled infusion of cefoxitin as a prophylactic antibiotic in colorectal surgical patients.

There are several limitations to the existing method of administering cefoxitin as a prophylactic antibiotic, and the limitations may be overcome by applying the target-concentration controlled infusion (TCI) method. Population pharmacokinetic parameters are required to administer cefoxitin by the TCI method. The aim of this study was to construct a new pharmacokinetic model of cefoxitin for the TCI method in colorectal surgical patients. In patients undergoing colorectal surgery, 2 g of cefoxitin was dissolved in 50 mL of saline and administered for 10 minutes prior to skin incision. Arterial blood samples were obtained at preset intervals to measure the total and free plasma concentrations of cefoxitin. Population pharmacokinetic analysis was performed using NONMEM software (ICON Development Solutions, Dublin, Ireland). Additionally, stochastic simulation was used to indirectly evaluate the effectiveness of the two administration methods (standard method vs TCI). In total, 297 plasma concentration measurements from 31 patients were used to characterize the pharmacokinetics of cefoxitin. A three-compartment mammillary model described the pharmacokinetics of cefoxitin. Body weight and creatinine clearance were significant covariates for clearance. The stochastic simulation showed that when compared with the standard method, the TCI method has a significantly higher fraction of time that the free concentration of cefoxitin is maintained above the minimum inhibitory concentration (P < .001). TCI has the potential to become a new infusion method for patient-tailored dosing in surgical patients. To administer cefoxitin via TCI in clinical practice, the newly constructed pharmacokinetic model should undergo proper external validation.

Population Pharmacokinetic Analysis of Amikacin for Optimal Pharmacotherapy in Korean Patients with Nontuberculous Mycobacterial Pulmonary Disease.

Amikacin is used as a therapy for patients with nontuberculous mycobacterial pulmonary disease (NTM-PD) who are resistant to macrolide antibiotics or have severe symptoms. This study aimed to characterize the pharmacokinetic properties of amikacin in patients with NTM-PD by developing a population pharmacokinetic model and to explore the optimal pharmacotherapy in patients with NTM-PD. For this study, all data were retrospectively collected. The amikacin pharmacokinetic properties were best described by a two-compartment model with first-order elimination. The estimated glomerular filtration rate and body weight were identified as significant covariates for clearance and the volume of distribution, respectively. A model-based simulation was conducted to explore the probability of reaching the target therapeutic range when various dose regimens were administered according to the body weight and renal function. The simulation results indicated that the amikacin dosage should be determined based on the body weight, and for patients who weigh over 70 kg, it is necessary to adjust the dose according to renal function. In conclusion, the optimal pharmacotherapy of amikacin for patients with NTM-PD was recommended based on the population pharmacokinetic model, which is expected to enable the personalization of drug therapy and improve the clinical outcomes of amikacin therapy.

CPX-351 Population Pharmacokinetics in Pediatric and Adult Patients with Acute Myeloid Leukemia (AML)

CPX-351 (Vyxeos®; daunorubicin and cytarabine liposome for injection), a dual-drug liposomal encapsulation of daunorubicin and cytarabine at a 1:5 synergistic ratio, is approved by the US FDA and EMA for the treatment of adults with newly diagnosed therapy-related AML or AML with myelodysplasia-related changes. Recently, CPX-351 was used in pediatric patients (pts) with relapsed AML (JCO 2020, ASH 2019, ASH 2018). A population pharmacokinetic (PK) analysis of plasma concentrations of cytarabine and daunorubicin following IV administration of CPX-351 was performed to assess sources of variability in PK and to determine if age-based dose adjustments may be warranted, particularly in pediatric pts. The PK population consisted of 250 pts with advanced hematologic malignancies from 7 studies and included 46 (18%) pediatric pts (1-17 y) and 204 (82%) adults (≥18 y). The population included 148 (59%) males, mainly of white origin (82%). Nonlinear mixed-effect modeling was performed using NONMEM®. Model evaluation and selection were assessed using a standard model discrimination process that included statistical criteria (eg, objective function value) and pertinent graphical representations of goodness-of-fit. Separate PK models were developed for cytarabine and daunorubicin; intrinsic and extrinsic factors were evaluated as covariates. The intrinsic factors included body weight, body mass index, age, sex, race, white blood cell count, and markers of renal function (creatinine clearance, serum creatinine) and hepatic function (bilirubin, aspartate and alanine aminotransferases, alkaline phosphatase). The extrinsic factors included study type (adult vs pediatric/young adult) and formulation (frozen vs lyophilized). Based on previous population PK models developed for adults, the PK models for cytarabine and daunorubicin used 2-compartment structural models, with drug input into the central compartment, first-order distribution between the central and peripheral compartments, and first-order elimination from the central compartment. Two-compartment structural models with body surface area (BSA) as an allometric scalar provided minimum bias in estimates of systemic clearance (CL) and volume of distribution for the central compartment (Vc). Based on the final population PK models, the estimates of CL and Vc in adults were 0.101 L/h and 4.76 L, respectively, for cytarabine and 0.140 L/h and 4.04 L for daunorubicin. The population estimates of CL and Vc for cytarabine in children, adolescents, and young adults (&amp;lt;22 y) were 0.073 L/h and 3.91 L, respectively, for cytarabine and 0.093 L/h and 3.28 L for daunorubicin. The population PK models included an allometric component that accounted for differences in BSA. The exponent for the effect of BSA on CL was 0.948 and 0.876 for cytarabine and daunorubicin, respectively, suggesting a faster clearance in pts with higher BSA. These differences in CL are expected to be offset by BSA-based dosing of CPX-351. Bilirubin and formulation (frozen) remained statistically significant covariates on the CL of daunorubicin. All tested covariates were eventually excluded from the population PK models, except BSA, bilirubin, study type, and formulation, which have a small effect on PK and are not expected to result in detectable changes in clinical safety or efficacy. Age was evaluated both as a continuous and categorical variable (1-5, 6-11, and 12-17 y) and was not a significant covariate for cytarabine and daunorubicin CL and Vc. Study type was identified as a significant covariate for CL and Vc for cytarabine and daunorubicin, which was possibly due to a change in analytical site for pediatric studies. Mean AUC0-48 values of cytarabine in pts aged 1-5, 6-11, and 12-17 y (135 U/m2) were similar (2767, 2783, and 2806 μg·h/mL, respectively) and approximately 40% higher than that observed in pts ≥18 y (100 U/m2, 1928 μg·h/mL), proportional to the 35% higher dose in pediatric pts. Mean AUC0-48 values of daunorubicin in pts aged 1-5, 6-11, and 12-17 y (135 U/m2) were similar (967, 896, and 982 μg·h/mL, respectively) and approximately 40% higher than that observed in pts ≥18 y (100 U/m2, 615 μg·h/mL), proportional to the 35% higher dose in pediatric pts. The results of this population PK analysis indicated exposures to CPX-351 in pediatric pts were not affected by age and were similar to those in adults when administered at the same BSA-normalized dose. Disclosures Wang: Jazz Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company. Cooper:Celgene: Other: Spouse was an employee of Celgene (through August 2019). Absalon:Jazz Pharmaceuticals: Research Funding. OffLabel Disclosure: Yes, in this study, CPX-351 was also evaluated in pediatric AML

Population Pharmacokinetic Model of Dexmedetomidine in a Heterogeneous Group of Patients.

Dexmedetomidine is a hepatically eliminated drug with sedative, anxiolytic, sympatholytic, and analgesic properties that has been increasingly used for various indications in the form of a short or continuous intravenous infusion. This study aimed to propose a population pharmacokinetic (PK) model of dexmedetomidine in a heterogeneous group of intensive care unit patients, incorporating 29 covariates potentially linked with dexmedetomidine PK. Data were collected from 70 patients aged between 0.25 and 88 years and treated with dexmedetomidine infusion for various durations at 1 of 4 medical centers. Statistical analysis was performed using a nonlinear mixed-effect model. Categorical and continuous covariates including demographic data, hemodynamic parameters, biochemical markers, and 11 single-nucleotide polymorphisms were tested. A 2-compartment model was used to describe dexmedetomidine PK. An allometric/isometric scaling was used to account for body weight difference in PK parameters, and the Hill equation was used to describe the maturation of clearance. Typical values of the central and peripheral volume of distribution and the systemic and distribution clearance for a theoretical adult patient were central volume of distribution = 22.50 L, peripheral volume of distribution = 86.1 L, systemic clearance = 34.7 L/h, and distribution clearance = 40.8 L/h. The CYP1A2 genetic polymorphism and noradrenaline administration were identified as significant covariates for clearance. A population PK model of dexmedetomidine was successfully developed. The proposed model is well calibrated to the observed data. The identified covariates account for <5% of interindividual variability and consequently are of low clinical significance for the purpose of dose adjustment.

Population Pharmacokinetic Analysis of Phenytoin After Intravenous Administration of Fosphenytoin in Adult and Elderly Epileptic Patients.

Fosphenytoin, the diphosphate ester salt of phenytoin, is widely used to treat status epilepticus. The aim of this study was to develop a population pharmacokinetic (PPK) model to describe serum phenytoin concentrations after the intravenous administration of fosphenytoin in adult and elderly epileptic patients. Patient backgrounds, laboratory tests, and prescribed drugs were retrospectively collected from electronic medical records. Patients who received fosphenytoin were enrolled. The PPK analysis was performed using NONMEM 7.3.0 with the first-order conditional estimation method with interaction. Age, sex, laboratory tests, and coadministered drugs were selected as candidates for covariates. Significance levels for forward inclusion and backward elimination were set at 0.05 and 0.01, respectively. The study protocol was approved by the Fukuoka Tokushukai Ethics Committee. A total of 340 serum phenytoin concentrations from 200 patients treated with fosphenytoin were available. The median age and body weight of the population were 71 years and 53.4 kg, respectively. A linear 1-compartment model with the conversion rate of fosphenytoin to phenytoin clearly described the pharmacokinetics of phenytoin after the intravenous administration of fosphenytoin. Age was detected as a covariate of clearance (CL): CL (L/h) = 1.99 × (body weight/53.4) × (age/71). Goodness-of-fit plots revealed the high-predictive performance of the final PPK model, and systematic deviations were not observed. The final model was validated by a prediction-corrected visual predictive check and bootstrap analysis. We herein developed a PPK model to describe phenytoin concentrations after the intravenous administration of fosphenytoin. Age was identified as a significant covariate for CL.

Population Pharmacokinetics of Intravenous Salbutamol in Children with Refractory Status Asthmaticus.

BackgroundIntravenous salbutamol is used to treat children with refractory status asthmaticus, however insufficient pharmacokinetic data are available to guide initial and subsequent dosing recommendations for its intravenous use. The pharmacologic activity of salbutamol resides predominantly in the (R)-enantiomer, with little or no activity and even concerns of adverse reactions attributed to the (S)-enantiomer.ObjectiveOur aim was to develop a population pharmacokinetic model to characterize the pharmacokinetic profile for intravenous salbutamol in children with status asthmaticus admitted to the pediatric intensive care unit (PICU), and to use this model to study the effect of different dosing schemes with and without a loading dose.MethodsFrom 19 children (median age 4.9 years [range 9 months–15.3 years], median weight 18 kg [range 7.8–70 kg]) treated with continuous intravenous salbutamol at the PICU, plasma samples for R- and S-salbutamol concentrations (111 samples), as well as asthma scores, were collected prospectively at the same time points. Possible adverse reactions and patients’ clinical data (age, sex, weight, drug doses, liver and kidney function) were recorded. With these data, a population pharmacokinetic model was developed using NONMEM 7.2. After validation, the model was used for simulations to evaluate the effect of different dosing regimens with or without a loading dose.ResultsA two-compartment model with separate clearance for R- and S-salbutamol (16.3 L/h and 8.8 L/h, respectively) best described the data. Weight was found to be a significant covariate for clearance and volume of distribution. No other covariates were identified. Simulations showed that a loading dose can result in higher R-salbutamol concentrations in the early phase after the start of infusion therapy, preventing accumulation of S-salbutamol.ConclusionsThe pharmacokinetic model of intravenous R- and S-salbutamol described the data well and showed that a loading dose should be considered in children. This model can be used to evaluate the pharmacokinetic–pharmacodynamic relationship of intravenous salbutamol in children, and, as a next step, the effectiveness and tolerability of intravenous salbutamol in children with severe asthma.Electronic supplementary materialThe online version of this article (10.1007/s40262-019-00811-y) contains supplementary material, which is available to authorized users.

Population pharmacokinetics of cyclosporine in Chinese children receiving hematopoietic stem cell transplantation.

Cyclosporine (CsA) is characterized by a narrow therapeutic window and high interindividual pharmacokinetic variability, particularly in juvenile patients. The aims of this study were to build a population pharmacokinetic model of CsA in Chinese children with hematopathy who received allogeneic hematopoietic stem cell transplantation (allo-HSCT) and to identify covariates affecting CsA pharmacokinetics. A total of 86 Chinese children aged 8.4 ± 3.8 years (range 1.1–16.8 years) who received allo-HSCT were enrolled. Whole blood samples were collected before allo-HSCT. Genotyping was performed using an Agena MassARRAY system. A total of 1010 trough plasma concentration values of CsA and clinical data were collected. The population pharmacokinetic model of CsA was constructed using nonlinear mixed-effects modeling (NONMEM) software. The stability and performance of the final model were validated using bootstrapping and normalized prediction distribution errors. We showed that a one-compartment model with first-order elimination adequately described the pharmacokinetics of CsA. The typical values for clearance (CL) and volume of distribution (V) were 42.3 L/h and 3100 L, respectively. Body weight, postoperative days, CYP3A4*1 G genotype, estimated glomerular filtration rate and coadministration of triazole antifungal drugs were identified as significant covariates for CL. Weight and postoperative days were significant covariates for the V of CsA. Our model can be adopted to optimize the CsA dosing regimen for Chinese children with hematopathy receiving allo-HSCT.

Population pharmacokinetic modeling to establish the role of P-glycoprotein on ciprofloxacin distribution to lung and prostate following intravenous and intratracheal administration to Wistar rats

Ciprofloxacin (CIP) is indicated for clinical treatment of urinary and respiratory tract infections. Poor infection site penetration and consequent insufficient exposure to the antimicrobial agent may be the reason for some therapeutic failures. Ciprofloxacin is reported as a substrate for efflux transporters, such as P-glycoprotein, which could be related to the presence of sub-therapeutic drug concentration at the infection site. In the present work we evaluated CIP pharmacokinetics (PK) in plasma and lung and prostate tissues of Wistar rats after intravenous (i.v.) and intratracheal (i.t.) dosing (7 mg/Kg) in the presence and absence of P-gp inhibitor tariquidar (TAR, 15 mg/Kg). Microdialysis was applied to determine free tissue concentration-time profiles and the obtained data were analyzed by non-compartmental and population PK (popPK) analysis. A sequential strategy was used to develop the popPK model: characterization of CIP PK in tissues (Tissue model) was performed subsequently to CIP PK modeling in plasma (Plasma model). Two and three compartmental models were used to simultaneously characterize plasma concentrations after i.t. and i.v. dosing; the distribution model was developed by separating the central compartment into venous and arterial compartment and by adding lung and prostate; TAR was identified as a significant covariate for clearance and volume of distribution of central compartment as well as for inter-compartmental clearance. Our results indicate an impact of P-gp on plasma PK, likely by acting on renal active secretion of CIP. Regarding CIP exposure in lung and prostate tissues, our results suggest a complex interplay between drug transporters; P-gp inhibition by TAR was likely counterbalanced by the activity of other efflux/influx transporters, which could not be fully characterized by our model.

Population Pharmacokinetics of Vancomycin in Pediatric Extracorporeal Membrane Oxygenation*

Describe the pharmacokinetics of vancomycin in pediatric patients undergoing extracorporeal membrane oxygenation and provide dosing recommendations to attain an area under the curve for 24 hours greater than 400 in this population. Retrospective, population pharmacokinetic analysis. PICU of a large tertiary care children's hospital. Population pharmacokinetic analysis and simulation were performed with NONMEM v7.3 (Icon, PLC, Dublin, Ireland). Patients less than 19 years old who received IV vancomycin and had serum vancomycin concentration monitoring while undergoing extracorporeal membrane oxygenation from January 1, 2011, to June 30, 2017. A total of 93 patients met study criteria (male 51%, median age 0.64 yr [interquartile range 0.07-6.7 yr]). Mean estimated creatinine clearance was 65 ± 47 mL/min/1.73 m. Patients received 1,116 vancomycin doses (14.6 ± 1.9 mg/kg/dose) and had 433 vancomycin serum concentrations (13.6 ± 6.9 mg/L) at 13.2 ± 10.7 hours after a dose. A two-compartment pharmacokinetic model with allometrically scaled weight on clearance (0.75) and volumes of distribution (1) was developed. Serum creatinine, postmenstrual age were significant covariates for clearance, patient age for central volume of distribution, and albumin for peripheral volume of distribution. Simulation identified a doses of 25-30 mg/kg/dose every 12-24 hours as having the highest percentage of patients with an area under the curve for 24 hours greater than 400 with the highest percentage trough concentrations in the less than 15 mg/L range. A vancomycin dose of 25-30 mg/kg/dose every 12-24 hours with serum concentration monitoring is a reasonable empiric dosing strategy to obtain an area under the curve for 24 hours greater than 400 in pediatric extracorporeal membrane oxygenation patients.

Population pharmacokinetics of serelaxin in patients with acute or chronic heart failure, hepatic or renal impairment, or portal hypertension and in healthy subjects.

Serelaxin is a recombinant human relaxin-2 peptide being developed for the treatment of acute heart failure (AHF). The present analyses aimed to evaluate serelaxin pharmacokinetics following intravenous administration and to identify covariates that may explain pharmacokinetic variability in healthy subjects and patients. Serum concentration-time data for 613 subjects from nine phase I and II studies were analysed using a nonlinear mixed-effects model to estimate population pharmacokinetics and identify significant covariates. A quantile regression analysis was also conducted to assess the relationship between clearance and covariates by including sparse data from a phase III study. A three-compartment disposition model was established to describe serelaxin pharmacokinetics. Three out of 23 covariates, including baseline body mass index (BMI) and estimated glomerular filtration rate (eGFR) and study A1201, were identified as significant covariates for clearance but with a moderate impact on steady-state concentration, reducing the intersubject variability from 44% in the base model to 41% in the final model with covariates. The steady-state volume of distribution (Vss) was higher in patients with AHF (544ml kg-1 ) or chronic heart failure (434ml kg-1 ), compared with typical nonheart failure subjects (347ml kg-1 ). Quantile regression analysis showed that a 20% increase in BMI or a 20% decrease in eGFR decreased serelaxin clearance by 9.2% or 5.2%, respectively. Patients with HF showed higher Vss but similar clearance (and therefore steady-state exposure) vs. non nonheart failure subjects. BMI and eGFR were identified as the main covariates explaining intersubject variability in clearance; however, the impact of these covariates on steady-state concentration was moderate and therefore unlikely to be clinically relevant.

Fixed dosing of intravenous tocilizumab in rheumatoid arthritis. Results from a population pharmacokinetic analysis.

Intravenous tocilizumab is currently dosed on body weight, although a weak correlation between body weight and clearance has been described. The aim of the study was to assess the current dosing strategy and provide a scientific rational for dosing using a modelling and simulation approach. Serum concentrations and covariates were obtained from intravenous tocilizumab treated subjects at a dose of 4, 6 or 8mg every 28days. A population pharmacokinetic analysis was performed using nonlinear mixed effects modelling. The final model was used to simulate tocilizumab exposure to assess a dosing strategy based on body weight or fixed dosing, using as target a cumulative area under the curve at 24weeks of treatment above 100 × 103 μghml-1 . A one-compartment disposition model with parallel linear and nonlinear elimination best described the concentration-time data. The typical population mean values for clearance, apparent volume of distribution, maximum elimination rate and Michaelis-Menten constant were 0.0104lh-1 , 4.83l, 0.239mgh-1 and 4.22μgml-1 , respectively. Interindividual variability was included for clearance (17.0%) and volume of distribution (30.8%). Significant covariates for clearance were patient body weight and C-reactive protein serum levels. An estimated exponent for body weight of 0.360 confirms the weak relationship with tocilizumab clearance. Simulations demonstrate that patients with lower weights are at risk of underdosing if the weight-based dosing approach is used. However, fixed-dosing provides a more consistent drug exposure regardless of weight category. Our study provides evidence to support fixed dosing of intravenous tocilizumab in rheumatoid arthritis patients since it reduces variability in tocilizumab exposure among weight categories compared to the current weight-based dosing approach.

Inflammation and Organ Failure Severely Affect Midazolam Clearance in Critically Ill Children.

Various in vitro, animal, and limited human adult studies suggest a profound inhibitory effect of inflammation and disease on cytochrome P-450 3A (CYP3A)-mediated drug metabolism. Studies showing this relationship in critically ill patients are lacking, whereas clearance of many CYP3A drug substrates may be decreased, potentially leading to toxicity. To prospectively study the relationship between inflammation, organ failure, and midazolam clearance as a validated marker of CYP3A-mediated drug metabolism in critically ill children. From 83 critically ill children (median age, 5.1 mo [range, 0.02-202 mo]), midazolam plasma (n = 532), cytokine (e.g., IL-6, tumor necrosis factor-α), and C-reactive protein (CRP) levels; organ dysfunction scores (Pediatric Risk of Mortality II, Pediatric Index of Mortality 2, Pediatric Logistic Organ Dysfunction); and number of failing organs were prospectively collected. A population pharmacokinetic model to study the impact of inflammation and organ failure on midazolam pharmacokinetics was developed using NONMEM 7.3. In a two-compartmental pharmacokinetic model, body weight was the most significant covariate for clearance and volume of distribution. CRP and organ failure were significantly associated with clearance (P < 0.01), explaining both interindividual and interoccasional variability. In simulations, a CRP of 300 mg/L was associated with a 65% lower clearance compared with 10 mg/L, and three failing organs were associated with a 35% lower clearance compared with one failing organ. Inflammation and organ failure strongly reduce midazolam clearance, a surrogate marker of CYP3A-mediated drug metabolism, in critically ill children. Hence, critically ill patients receiving CYP3A substrate drugs may be at risk of increased drug levels and associated toxicity.

Etrolizumab Population Pharmacokinetics (Pop PK) and Covariate Analysis in Patients With Moderately to Severely Active Ulcerative Colitis (UC)

Introduction: Etrolizumab is a humanized IgG1 monoclonal antibody that specifically binds the β7 subunit of α4β7 and αEβ7 integrins. Clinical activity of etrolizumab has been observed in patients with moderate-to-severe UC in a phase 2 trial. The objective of this Pop PK analysis was to characterize covariate effects on the PK profile of etrolizumab. Methods: This analysis included data from 145 etrolizumab-treated patients from 3 studies: a phase 1 dose-escalation study (single doses at 0.3, 1, 3 or 10 mg/kg intravenously [IV] or 3 mg/kg subcutaneously [SC] or 3 monthly doses at 0.5, 1.5 or 3 mg/kg SC or 4 mg/kg IV), a phase 2 efficacy and safety study (2 SC dose cohorts of 100 mg at weeks 0, 4 and 8 or 420 mg at week 0 followed by 300 mg at weeks 2, 4 and 8) and a phase 2 open-label extension study (300 mg SC monthly). A stepwise forward addition and backward elimination approach was used to evaluate the impact of the following baseline covariates on etrolizumab PK: age, sex, body weight (BW), Mayo Clinic score, albumin, C-reactive protein, fecal calprotectin, prior use and response to anti-tumor necrosis factor α biologics and concomitant treatment with steroids or immunosuppressants. The Pop PK analysis was performed using NONMEM 7.1.2. Results: A 2-compartmental model with first-order absorption and elimination kinetics described etrolizumab PK well. BW and baseline serum albumin were identified as significant covariates for clearance (CL) (p<0.001); each explained 16% and 30% of the interindividual variability (IIV) of CL, respectively. Simulation showed similar exposure variability for a BW-based-dose or a fixed-dose. No other covariates were found to have significant impact on etrolizumab PK. The final model estimated the typical population CL value and central volume of distribution to be 0.245 L/day and 3.2 L, respectively. The elimination half-life and SC bioavailability were estimated to be 11 days and 53%, respectively. The IIV of evaluated PK parameters ranged from 19% to 67%. Pop PK simulation estimated that 100 mg nominal dose (105 mg actual dose) every 4 weeks, the proposed phase 3 dose regimen, can maintain a steady-state trough concentration of >1.7 μg/mL in 85% of patients (1.7 μg/mL is the observed minimum drug level associated with full β7 receptor occupancy in peripheral blood and colonic tissue). Conclusion: Etrolizumab exhibited linear PK at the target therapeutic dose. Based on the available data, BW and baseline serum albumin were identified as statistically significant covariates for CL. However, given the favorable safety and efficacy profiles for etrolizumab, the impact of these covariates on the therapeutic outcome is expected to be minimal and not clinically relevant. Disclosure - Xiaohui (Tracey) Wei, Diana Luca, Yehong Wang, Sharon O’Byrne, Rich Erickson, John D. Davis and Meina T. Tang are employees of Genentech, Inc.