Population Pharmacodynamic Model Research Articles

Nedosiran population pharmacokinetic and pharmacodynamic modelling and simulation to guide clinical development and dose selection in patients with primary hyperoxaluria type 1.

To characterize pharmacokinetic and pharmacodynamic profiles of nedosiran in patients with primary hyperoxaluria type 1 (PH1), identify influential covariates and confirm therapeutic doses. A population pharmacokinetic (PK)/pharmacodynamic (PD) (POP-PKPD) model was developed to characterize the concentration-time course of nedosiran and the corresponding effect on 24-h urinary oxalate (Uox). Simulations of dosing to achieve clinically meaningful reduction in Uox in children, adolescents and adults with PH1 were performed. Analyses included PK data from 143 healthy participants and PH1/PH2 patients, and PD data from 46 PH1 patients. Nedosiran PK was described by a two-compartment model with dual n-transit absorption and parallel linear and nonlinear elimination. The relationship between nedosiran exposure and Uox was described by an indirect response model. Body weight, estimated glomerular filtration rate (eGFR) and disease status were identified as influential covariates for the POP-PK model. The simulation results supported a weight-banded dosing regimen of nedosiran sodium in adolescents and adults (≥12 years) with PH1 of 170 mg (weight ≥50 kg) and 136 mg (weight <50 kg), in children (6-11 years) with PH1 of 3.5mg/kg, and no dose adjustments for PH1 patients with relatively preserved kidney function (eGFR ≥ 30 mL/min/1.73m2). Following the proposed dosing regimens, the simulated median fold-changes in PK AUC0-τ,ss were acceptable (≤1.51 fold-change) and ~71% of PH1 patients across all age groups achieved near-normal Uox (<0.6mmol) by week 52. The final POP-PKPD model characterizes observed nedosiran PK and Uox data. Simulations support nedosiran dosing regimens in PH1 patients aged ≥6years with relatively preserved kidney function.

Pharmacokinetic-pharmacodynamic modelling and simulation of methotrexate dosing in patients with rheumatoid arthritis.

To develop a non-linear mixed-effects population pharmacokinetic and pharmacodynamic (PK-PD) model describing the change in the concentration of methotrexate polyglutamates in erythrocytes (ery-MTX-PGn with "n" number of glutamate, representing PK component) and how this relates to modified 28-joint Disease Activity Score incorporating erythrocyte sedimentation rate (DAS-28-3) for rheumatoid arthritis (RA), representing PD component. An existing PK model was fitted to data from a study consisting of 117 RA patients. The estimation of population PK-PD parameters was performed using stochastic approximation expectation maximisation algorithm in Monolix 2021R2. The model was used to perform Monte Carlo simulations of a loading dose regimen (50mg subcutaneous methotrexate as loading doses, then 20mg weekly oral methotrexate) compared to a standard dosing regimen (10mg weekly oral methotrexate for 2 weeks, then 20mg weekly oral methotrexate). Every 40 nmol/L increase in ery-MTX-PG3-5 total concentration correlated with 1-unit reduction in DAS-28-3. Significant covariate effects on the therapeutic response of methotrexate included the use of prednisolone in the first 4 weeks (positive use correlated with 25% reduction in DAS-28-3 when other variables were constant) and patient age (every 10-year increase in age correlated with 3.4% increase in DAS-28-3 when other variables were constant). 4 methotrexate loading doses led to a higher percentage of patients achieving a good/moderate response compared to the standard regimen (Week 4: 87.6% vs. 39.8%; Week 10: 64.7% vs. 57.0%). A loading dose regimen was more likely to achieve higher ery-MTX-PG concentration and better therapeutic response after 4 weeks of methotrexate treatment.

Sample Size Determination and Study Design Impact on Dose-Scale Pharmacodynamic Bioequivalence: a Case Study Using Orlistat.

Dose-scale pharmacodynamic bioequivalence is recommended for evaluating the consistency of generic and innovator formulations of certain locally acting drugs, such as orlistat. This study aimed to investigate the standard methodology for sample size determination and the impact of study design on dose-scale pharmacodynamic bioequivalence using orlistat as the model drug. A population pharmacodynamic model of orlistat was developed using NONMEM 7.5.1 and utilized for subsequent simulations. Three different study designs were evaluated across various predefined relative bioavailability ratios of test/reference (T/R) formulations. These designs included Study Design 1 (2×1 crossover with T1 60 mg, R1 60 mg, and R2 120 mg), Study Design 2 (2×1 crossover with T2 120 mg, R1 60 mg, and R2 120 mg), and Study Design 3 (2×2 crossover with T1 60 mg, T2 120 mg, R1 60 mg, and R2 120 mg). Sample sizes were determined using a stochastic simulation and estimation approach. Under the same T/R ratio and power, Study Design 3 required the minimum sample size for bioequivalence, followed by Study Design 1, while Study Design 2 performed the worst. For Study Designs 1 and 3, a larger sample size was needed on the T/R ratio < 1.0 side for the same power compared to that on the T/R ratio > 1.0 side. The opposite asymmetry was observed for Study Design 2. We demonstrated that Study Design 3 is most effective for reducing the sample size for orlistat bioequivalence studies, and the impact of T/R ratio on sample size shows asymmetry.

Population pharmacokinetic, pharmacodynamic and efficacy modeling of SB12 (proposed eculizumab biosimilar) and reference eculizumab

PurposeTo describe, compare similarity of pharmacokinetic (PK), pharmacodynamic (PD) and efficacy of SB12 and reference eculizumab (ECU) and find clinically significant covariate relationships.MethodsThe PK, PD (terminal complement activity) and efficacy (LDH) data of SB12 and ECU were obtained from 289 subjects from phase I and phase III studies. One- and two-compartment PK models with first-order elimination were evaluated for SB12 and ECU. For PD and efficacy, both direct and indirect models were tested. The impact of covariates on PK, PD and efficacy parameters was assessed. Relationship between PK/PD and PD/efficacy was characterized. This modeling was performed using NONMEM version 7.4 (Icon Development Solutions, Ellicott City, MD, USA).ResultsThe two-compartment model adequately described the PK of SB12 and ECU, and the subject’s weight was chosen as a clinically significant covariate affecting drugs’ clearance and central volume of distribution. Treatment group was not a significant covariate affecting clearance. The direct response model using inhibitory sigmoid Emax and sigmoid Emax relationship well described the PK/PD relationship and PD/efficacy relationship of SB12 and ECU, respectively. Through this modeling, the relationships between PK, PD and efficacy were characterized. There were no differences in PK, PD and efficacy parameters between SB12 and ECU in pooled populations of healthy subjects and paroxysmal nocturnal haemoglobinuria (PNH) patients.ConclusionThe population modeling showed PK, PD and efficacy similarities between SB12 and ECU in pooled population of healthy subjects and PNH patients, supporting the totality of evidence on biosimilarity for SB12.

Dosing optimization of rituximab for primary membranous nephropathy by population pharmacokinetic and pharmacodynamic study.

Primary membranous nephropathy (PMN) is the most common cause for adult nephrotic syndrome. Rituximab has demonstrated promising clinical efficacy by random controlled trials and the off-label use is widely adopted in PMN. However, the standard dosage is borrowed from B cell lymphoma treatment with far more antigens and is oversaturated for PMN treatment, accompanied with additional safety risk and unnecessary medical cost. More than 15% serious adverse events were observed under standard dosage and low dose therapies were explored recently. Dose optimization by clinical trials is extremely time- and cost-consuming and can be significantly accelerated with the aid of model-informed drug development. Here, we aim to establish the first population pharmacokinetic and pharmacodynamic (PPK/PD) model for rituximab in PMN to guide its dosage optimization. Rituximab pharmacokinetic and pharmacodynamic data from 41 PMN patients in a retrospective study under a newly proposed monthly mini-dose were used to construct quantitative dose-exposure-response relationship via mechanistic target-mediated drug disposition (TMDD) model followed by regression between the reduction of anti-PLA2R titer and time after the treatment. The final model, validated by goodness-of-fit plots, visual predictive checks and bootstrap, was used to recommend the optimized dosing regimen by simulations. The model was well validated for PK/PD prediction. The systemic clearance and half-life are 0.54L/h and 14.7 days, respectively. Simulation of a novel regimen (6 monthly doses of 100mg) indicated the comparable ability and superior duration time of CD20+ B cell depletion compared with standard dosage, while the cumulative dosage and safety risk was significantly decreased. We established the first PPK/PD model and provide evidence to support the dosage optimization based on monthly mini-dose. Our study can also efficiently accelerate dosage optimization of novel anti-CD20 antibodies in PMN and other indications.

Population pharmacokinetics, enzyme occupancy, and pharmacodynamic modeling of soticlestat in patients with developmental and epileptic encephalopathies.

Soticlestat (TAK-935) is a first-in-class, selective inhibitor of cholesterol 24-hydroxylase (CH24H) under phase III development for the treatment of the developmental and epileptic encephalopathies (DEEs), Dravet syndrome (DS), and Lennox-Gastaut syndrome (LGS). A previous model characterized the pharmacokinetics (PKs), CH24H enzyme occupancy (EO), and pharmacodynamics (PDs) of soticlestat in healthy volunteers. The present study extended this original model for patients with DEEs and investigated sources of variability. Model-based simulations were carried out to optimize dosing strategies for use in clinical trials. Data from eight phase I and II trials of healthy volunteers or patients with DEEs receiving oral soticlestat 15-1350 mg were included, encompassing 218 individuals for population PK (PopPK) analyses and 306 individuals for PK/PD analyses. Dosing strategies were identified through model-based simulations. The final mixed-effect PopPK/EO/PD model consisted of a two-compartment PK model and an effect-site compartment in the PK/EO model; soticlestat concentrations at the effect site were linked to 24S-hydroxycholesterol plasma concentrations using a semimechanistic inhibitory indirect response model. Covariates were included to account for sources of variability. Pediatric dosing strategies were developed for four body weight bands (10 to <15, 15 to <30, 30 to <45, and 45-100 kg) to account for covariate effects by body weight. The final PopPK and PK/EO/PD models accurately described PK, EO, and PD profiles of soticlestat in healthy volunteers and patients with DEEs. Covariate analyses and model-based simulations facilitated optimization of phase III trial dosing strategies for patients with DS or LGS.

Population Pharmacodynamic Models of Risperidone on PANSS Total Scores and Prolactin Levels in Schizophrenia.

Currently, research predominantly focuses on evaluating clinical effects at specific time points while neglecting underlying patterns within the treatment process. This study aims to analyze the dynamic alterations in PANSS total scores and prolactin levels in patients with schizophrenia treated with risperidone, along with the influencing covariates. Using data from an 8-week randomized, double-blind, multicenter clinical trial, a population pharmacodynamic model was established for the PANSS total scores of and prolactin levels in patients treated with risperidone. The base model employed was the Emax model. Covariate selection was conducted using a stepwise forward inclusion and backward elimination approach. A total of 144 patients were included in this analysis, with 807 PANSS total scores and 531 prolactin concentration values. The PANSS total scores of the patients treated with risperidone decreased over time, fitting a proportionally parameterized sigmoid Emax model with covariates including baseline score, course of the disease, gender, plasma calcium ions, and lactate dehydrogenase levels. The increase in prolactin levels conformed to the ordinary Emax model, with covariates encompassing course of the disease, gender, weight, red blood cell count, and triglyceride levels. The impacts of the baseline scores and the course of the disease on the reduction of the PANSS scores, as well as the influence of gender on the elevation of prolactin levels, each exceeded 20%. This study provides valuable quantitative data regarding PANSS total scores and prolactin levels among patients undergoing risperidone treatment across various physiological conditions.

Population Pharmacokinetic and Pharmacodynamic Modeling of Romiplostim Biosimilar GP40141 and Reference Product in Healthy Volunteers to Evaluate Biosimilarity.

GP40141 is a romiplostim biosimilar. A Phase 1 clinical trial was previously conducted in healthy volunteers to evaluate the pharmacodynamics (PD), pharmacokinetics (PK), and safety of GP40141 compared to the reference romiplostim (NCT05652595). Using noncompartmental analysis, the biosimilarity of PD end points was determined according to the classical criterion (0.8-1.25). PK end points were also in good agreement between GP40141 and the reference romiplostim; however, the confidence interval for the area under concentration-time curve from time 0 to the time of last measurement was slightly out of the bioequivalence range (0.91-1.29). Population PK/PD was used in the present study to characterize the individual PK and PD data of 56 healthy subjects in 2 cross-over periods of the Phase 1 clinical trial. Body weight and neutralizing antibodies to romiplostim were found to be important predictors of apparent volume of distribution and linear elimination constant, respectively. Within the framework of the conducted modeling, population estimates of PK/PD parameters were obtained, which were in agreement with literature data for the reference romiplostim. Additionally, values of intersubject variability, previously unreported for romiplostim in a healthy subject population, were derived. Covariate analysis, conducted during model development, as well as visual diagnostics and model-based simulations, demonstrated the absence of significant differences in PK and PD between GP40141 and romiplostim-ref.

Population pharmacokinetic/pharmacodynamic modeling and exposure-response analysis of ciprofol in the induction and maintenance of general anesthesia in patients undergoing elective surgery: A prospective dose optimization study

AimThis study aimed to establish a population pharmacokinetic and pharmacodynamic (PK-PD) model to explore the optimal maintenance dose and appropriate starting time of maintenance dose after induction of ciprofol and investigate the efficacy and safety of ciprofol for general anesthesia induction and maintenance in patients undergoing elective surgery. MethodA total of 334 subjects with 3092 concentration measurements from nine clinical trials and 115 subjects with 5640 bispectral index (BIS) measurements from two clinical trials were used in the population PK-PD analysis. Exposure-response relationships for both efficacy endpoints (duration of anesthesia successful induction, time to recovery from anesthesia, time to respiratory recovery, and time from discontinuation to the 1st/3rd consecutive Aldrete score ≥ 9) and safety variables (hypotension, bradycardia, and injection site pain) were evaluated based on the data gathered from 115 subjects in two clinical trials. ResultCiprofol pharmacokinetics (PK) were adequately described by a three-compartment model with first-order elimination from the central compartment and redistribution from the deep and shallow peripheral compartments. An inhibitory sigmoidal Emax model best described the relationship between ciprofol effect-site concentrations and BIS measurements. Body weight, age, sex, blood sampling site, and study type (short-term infusion vs long-term infusion) were identified as statistically significant covariates on the PK of ciprofol. No covariates were found to have a significant effect on the pharmacodynamic (PD) parameters. The PK-PD simulation results showed that the optimal maintenance dose was 0.8 mg/kg/h and the appropriate time to start the maintenance dose was 4–5 mins after the induction dose of ciprofol. Within the exposure range of this study, no meaningful correlations between ciprofol exposures and efficacy or safety endpoints were observed. ConclusionA population PK-PD model was successfully developed to describe the ciprofol PK and BIS changes. Efficacy was consistent across the exposure range with a well-tolerated safety profile indicating no maintenance dose adjustment is required for patients undergoing elective surgery.

Abstract 12412: In Silico Evaluation of Dosing Regimens to Accommodate Coadministration of Mavacamten With Strong Inhibitors of Cytochrome P450 3A4 and Moderate Inhibitors of Cytochrome P450 2C19 in Patients With Obstructive Hypertrophic Cardiomyopathy

Background: Mavacamten is primarily metabolized by cytochrome P450 enzymes CYP2C19 and CYP3A4 and coadministration with strong CYP3A4 or moderate CYP2C19 inhibitors is contraindicated in patients with obstructive hypertrophic cardiomyopathy (HCM) in the US prescribing information (USPI). Aim: To assess the safety and efficacy of accommodating coadministration of mavacamten with strong CYP3A4 and moderate CYP2C19 inhibitors via simulations. Methods: Simulations of 5000 virtual patients with obstructive HCM uniformly distributed by CYP2C19 metabolizer phenotypes were performed using population pharmacokinetic and pharmacodynamic models. The USPI posology and variations were simulated to evaluate if short term (1 week) and long term (chronic) coadministration of CYP3A4 or CYP2C19 inhibitors could be accommodated. Analogous to USPI posology development, comparisons were made by evaluating proportions of patients with left ventricular ejection fraction [LVEF] &lt; 50% (safety) and Valsalva left ventricular outflow tract gradient [VLVOTg] &lt; 30 mmHg (efficacy). Results: When initiating mavacamten with a CYP3A4 inhibitor, a posology using 2.5 mg starting dose, with coadministration stopped if LVEF &lt; 50% at 2.5 mg, resulted in a similar peak proportion of CYP2C19 poor metabolizers with LVEF &lt; 50% (5.7%) and LVEF &lt; 40% (0.9%) compared to the USPI (2.7% and 0.3% respectively; Table ). When initiating mavacamten with a CYP2C19 inhibitor, a 2.5 mg starting dose resulted in a similar peak proportion of LVEF &lt; 50% in CYP2C19 ultrarapid metabolizers to USPI. Optimal efficacy was achieved; in some patients, this was delayed owing to dose reduction. Interruption of mavacamten during short term administration of inhibitors transiently increased VLVOTg for the duration of interruption, with no effect on LVEF. Conclusion: Coadministration of mavacamten with CYP3A4 or CYP2C19 inhibitors could be accommodated within the titration scheme with dose interruption or down titration.

Fitusiran Population Pharmacokinetic and Pharmacodynamic Modeling Utilizing Phase 3 Clinical Trial Data to Confirm Doses Tested in Phase 3 Trials to Support an Antithrombin-Based Dose Regimen

Background: Fitusiran is an investigational siRNA therapeutic designed to target antithrombin (AT) with the goal of rebalancing hemostasis in people with hemophilia (PwH) A or B, regardless of inhibitor status. A semi-mechanistic population pharmacokinetic/pharmacodynamic (PopPK/PD) model using Phase 1/2 data from 1000 virtual PwH was previously developed to inform dose selection for the Phase 3 program using a fitusiran AT-based dosing regimen. This indicated that a starting dose of 50 mg once every 2 months (Q2M) would maintain AT activity between 15-35% for a considerable number of PwH, and aim to mitigate the risk of thrombosis and preserve bleed control. This analysis presents an updated fitusiran PopPK/PD model using pooled Phase 1/2 and Phase 3 AT activity data to guide an AT-based dose regimen for Phase 3 trials in adults with hemophilia. Methods: Plasma AT activity data from Phase 1 (NCT02035605), Phase 1/2 (NCT02554773) and Phase 3 studies (NCT03417102, NCT03417245, NCT03549871) in PwH A/B, with or without inhibitors were pooled to update the PopPK/PD model. Pooled AT activity data generated a large dataset with diverse populations and allowed for the evaluation of potential effects of intrinsic and/or extrinsic factors as covariates on AT activity in the targeted hemophilia population. The final PopPK/PD model was used to simulate AT activity at various dosing regimens in 1500 virtual PwH to select the final AT-based dosing regimen. Results: ThePopPK/PD dataset included 44059 AT activity observations from 339 participants. An indirect response model (Figure 1) well described the dynamics of AT activity and intra-individual variability. The covariate effects identified in the PopPK/PD model were White race on Kout (increase in elimination rate of AT) and half maximal inhibitory concentration (IC50; increase in model derived potency estimate), bodyweight on Kout (increase with bodyweight), age with IC50 (increase with age). Simulations predict that with a starting dose of 50 mg Q2M, &amp;gt;58% of PwH would achieve AT activity &amp;gt;15% (10 th percentile trough-AT activity was 15.3%). Mean peak AT activity is projected to be 24.7 ± 10%. For PwH with &amp;gt;35% AT activity, a dose escalation to 50 mg every month (QM) would be required to achieve target AT activity &amp;lt;35%. It is predicted that 0.8% of PwH would then be escalated to 80mg QM in a stepwise manner. With the starting dose of 50 mg Q2M, 41.7% of PwH are predicted to have AT activity &amp;lt;15%; these PwH should be de-escalated to 20 mg Q2M. At a dose of 20 mg Q2M, 10.2% would have AT activity &amp;lt;15% (Figure 2). Conclusions: PopPK/PD model simulations confirm that the fitusiran AT-based dose regimen with a starting dose of 50 mg Q2M that can be escalated or de-escalated maintains the target AT range of 15-35% in the majority of PwH. It is predicted approximately 88% of PwH will require zero or one dose change. The efficacy and safety of the fitusiran AT-based dose regimen is being evaluated in ongoing clinical trials.

Population Pharmacodynamic Modelling of the CD19+ Suppression Effects of Rituximab in Paediatric Patients with Neurological and Autoimmune Diseases.

Limited pharmacotherapy and the failure of conventional treatments in complex pathologies in children lead to increased off-label use of rituximab. We aimed to characterize the time course of CD19+ B lymphocytes (CD19+) under treatment with intravenous rituximab in children with neurologic and autoimmune diseases and to evaluate the impact of covariates (i.e., demographics, diagnosis and substitution between innovator and biosimilar product) on rituximab pharmacodynamics and disease activity. Pre- and post-drug infusion CD19+ in peripheral blood were prospectively registered. A population pharmacodynamic model describing the time course of CD19+ was developed with NONMEM v7.4. Simulations of three different rituximab regimens were performed to assess the impact on CD19+. Logistic regression analysis was performed to identify predictors of clinical response recorded through disease activity scores. 281 measurements of CD19+ lymphocyte counts obtained from 63 children with neurologic (n = 36) and autoimmune (n = 27) diseases were available. The time course of CD19+ was described with a turn-over model in which the balance between synthesis and degradation rates is disrupted by rituximab, increasing the latter process. The model predicts half-lives (percent coefficient of variation, CV(%)) of rituximab and CD19+ of 11.6 days (17%) and 173.3 days (22%), respectively. No statistically significant effect was found between any of the studied covariates and model parameters (p > 0.05). Simulations of different regimens showed no clinically significant differences in terms of CD19+ repopulation times. A trend towards a lack of clinical response was observed in patients with lower CD19+ repopulation times and higher areas under the CD19+ versus time curve. Rituximab pharmacodynamics was described in a real-world setting in children suffering from autoimmune and neurologic diseases. Diagnosis, substitution between innovator rituximab and its biosimilars or type of regimen did not affect rituximab-induced depletion of CD19+ nor the clinical response in this cohort of patients. According to this study, rituximab frequency and dosage may be chosen based on clinical convenience or safety reasons without affecting CD19+ repopulation times. Further studies in larger populations are required to confirm these results.

Model-informed precision dosing in vancomycin treatment.

Introduction: While vancomycin remains a widely prescribed antibiotic, it can cause ototoxicity and nephrotoxicity, both of which are concentration-associated. Overtreatment can occur when the treatment lasts for an unnecessarily long time. Using a model-informed precision dosing scheme, this study aims to develop a population pharmacokinetic (PK) and pharmacodynamic (PD) model for vancomycin to determine the optimal dosage regimen and treatment duration in order to avoid drug-induced toxicity. Methods: The data were obtained from electronic medical records of 542 patients, including 40 children, and were analyzed using NONMEM software. For PK, vancomycin concentrations were described with a two-compartment model incorporating allometry scaling. Results and discussion: This revealed that systemic clearance decreased with creatinine and blood urea nitrogen levels, history of diabetes and renal diseases, and further decreased in women. On the other hand, the central volume of distribution increased with age. For PD, C-reactive protein (CRP) plasma concentrations were described by transit compartments and were found to decrease with the presence of pneumonia. Simulations demonstrated that, given the model informed optimal doses, peak and trough concentrations as well as the area under the concentration-time curve remained within the therapeutic range, even at doses smaller than routine doses, for most patients. Additionally, CRP levels decreased more rapidly with the higher dose starting from 10days after treatment initiation. The developed R Shiny application efficiently visualized the time courses of vancomycin and CRP concentrations, indicating its applicability in designing optimal treatment schemes simply based on visual inspection.

Anti-inflammatory effects of dexamethasone in COVID-19 patients: Translational population PK/PD modeling and simulation.

Dexamethasone (DEX) given at a dose of 6 mg once-daily for 10 days is a recommended dosing regimen in patients with coronavirus disease 2019 (COVID-19) requiring oxygen therapy. We developed a population pharmacokinetic and pharmacodynamic (PopPK/PD) model of DEX anti-inflammatory effects in COVID-19 and provide simulations comparing the expected efficacy of four dosing regimens of DEX. Nonlinear mixed-effects modeling and simulations were performed using Monolix Suite version 2021R1 (Lixoft, France). Published data for DEX PK in patients with COVID-19 exhibited moderate variability with a clearance of about half that in healthy adults. No accumulation of the drug was expected even with daily oral doses of 12 mg. Indirect effect models of DEX inhibition of TNFα, IL-6, and CRP plasma concentrations were enacted and simulations performed for DEX given at 1.5, 3, 6, and 12 mg daily for 10 days. The numbers of individuals that achieved specified reductions in inflammatory biomarkers were compared among the treatment groups. The simulations indicate the need for 6 or 12 mg daily doses of DEX for 10 days for simultaneous reductions in TNFα, IL-6, and CRP. Possibly beneficial is DEX given at a dose of 12 mg compared to 6 mg. The PopPK/PD model may be useful in the assessment of other anti-inflammatory compounds as well as drug combinations in the treatment of cytokine storms.

Population model-based analysis of the memory B-cell response following belimumab therapy in the treatment of systemic lupus erythematosus.

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by B-cell hyperactivity and breach of tolerance. Autoreactive memory B cells, which have a decreased activation threshold and the ability to survive in absence of antigen, are believed to contribute to chronicity in autoimmune diseases like SLE. Belimumab, the first approved biological treatment of active SLE and lupus nephritis, reduces B cells dependent on B-lymphocyte stimulator protein (BLyS) for survival, whereas memory B cells are spared; several studies reported circulating memory B-cell concentrations increase following BLyS neutralization. This analysis investigated the effect of dose, demographics, and disease status on memory B-cell response after starting belimumab treatment. Population pharmacodynamic models were fitted to a pooled dataset from seven belimumab SLE trials. The optimal model was selected using maximum likelihood methods and was then refit to the data using Bayesian analysis and used to simulate memory B-cell response by belimumab dose and covariate subgroups. At the belimumab approved doses (10mg/kg intravenously every 4 weeks, 200 mg subcutaneously every week), circulatory memory B cells increase in the first 4-8 weeks after belimumab initiation, typically returning to baseline levels over 76 weeks. The model analysis suggested belimumab stimulates memory B-cell transition from lymphoid and/or inflamed tissues into the circulation, rather than inhibiting trafficking in the reverse direction. Baseline BLyS and anti-double-stranded deoxyribonucleic acid antibody concentrations were statistically identifiable covariates of memory B-cell response, although their impact on predicting size and response duration was small.

Population pharmacokinetic and pharmacodynamic model of propofol externally validated in Korean elderly subjects.

The Eleveld propofol pharmacokinetic (PK) model, which was developed based on a broad range of populations, showed greater bias (- 27%) in elderly subjects in a previous validation study conducted by Vellinga and colleagues. We aimed to develop and externally validate a new PK-pharmacodynamic (PK-PD) model of propofol for elderly subjects. A population PK-PD model was constructed using propofol plasma concentrations and bispectral index (BIS) values that were obtained from 31 subjects aged 65years older in previously published phase I studies. The predictive performance of the newly-developed PK-PD model (Choi model) was assessed in a separate Korean elderly population and compared with that of the Eleveld model. A three-compartment mammillary model using an allometric expression and a sigmoid Emax model well-described the time courses of propofol concentrations and BIS values. The V1, V2, V3, Cl, Q1, Q2, E0, Emax, Ce50, γ, and ke0 of a 60-kg subject were 8.36, 58.0, 650 L, 1.26, 0.917, 0.669 L/min, 92.1, 18.7, 2.21μg/mL, 2.89, and 0.138 /min, respectively. In the Choi model and Eleveld model, pooled biases (95% CI) of the propofol concentration were 7.78 (3.09-12.49) and 16.70 (9.46-23.93) and pooled inaccuracies were 22.84 (18.87-26.81) and 24.85 (18.07-31.63), respectively. The Choi PK model was less biased than the Eleveld PK model in Korean elderly subjects (age range: 65.0-79.0yr; weight range: 45.0-75.3kg). Our results suggest that the Choi PK model, particularly, is applicable to target-controlled infusion in non-obese Korean elderly subjects.

Prospective Validation and Refinement of a Population Pharmacokinetic Model of Fludarabine in Children and Young Adults Undergoing Hematopoietic Cell Transplantation.

Fludarabine is a nucleoside analog with antileukemic and immunosuppressive activity commonly used in allogeneic hematopoietic cell transplantation (HCT). Several fludarabine population pharmacokinetic (popPK) and pharmacodynamic models have been published enabling the movement towards precision dosing of fludarabine in pediatric HCT; however, developed models have not been validated in a prospective cohort of patients. In this multicenter pharmacokinetic study, fludarabine plasma concentrations were collected via a sparse-sampling strategy. A fludarabine popPK model was evaluated and refined using standard nonlinear mixed effects modelling techniques. The previously described fludarabine popPK model well-predicted the prospective fludarabine plasma concentrations. Individuals who received model-based dosing (MBD) of fludarabine achieved significantly more precise overall exposure of fludarabine. The fludarabine popPK model was further improved by both the inclusion of fat-free mass instead of total body weight and a maturation function on fludarabine clearance. The refined popPK model is expected to improve dosing recommendations for children younger than 2 years and patients with higher body mass index. Given the consistency of fludarabine clearance and exposure across its multiple days of administration, therapeutic drug monitoring is not likely to improve targeted exposure attainment.

Population pharmacokinetic and pharmacodynamic modeling of evobrutinib in healthy adult participants.

Evobrutinib, a Bruton's tyrosine kinase (BTK) inhibitor, has shown therapeutic potential in relapsing multiple sclerosis. This analysis aimed to develop pharmacokinetic (PK) and pharmacodynamic (PD; BTK occupancy [BTKO]) models of evobrutinib and simulate PK and BTKO profiles under alternative dosing regimens. Data were obtained from two phase I evobrutinib studies in healthy adult participants (Japanese and non-Japanese). Overall, 2326 observations were available from 76 participants; n =42 from Study MS200527_0017 Part A received evobrutinib 25, 75, or 200 mg once-daily oral doses for 6 days while fasted; n = 18 from Study MS200527_0019 and n =16 from Study MS200527_0017 Part B received single evobrutinib 75 mg oral doses with food (low-fat meal) and while fasted. Population PK/PD modeling for evobrutinib concentrations and BTKO (fraction unbound) were performed using nonlinear mixed-effects modeling. The effect of once-daily/twice-daily regimens and doses of 10-200 mg on BTKO were simulated. A two-compartment model with sequential zero-first order absorption and first-order elimination adequately described the data. Bioavailability increased by 49% with food compared with when fasted. There was no difference in PK parameters between Japanese and non-Japanese participants. The BTKO profile of evobrutinib was described by the irreversible binding population model. The simulated percentage of participants with minimum BTKO increased in a dose-dependent manner across the BTKO thresholds of interest (70%, 80%, 90%, and 95% occupancy). Evobrutinib doses of 25 mg once-daily, 50 mg twice-daily, or 75 mg twice-daily while fasted are possible choices for further development, assuming BTKO ≥70% at trough is needed to achieve efficacy.

Relationship of tafamidis binding site occupancy, transthyretin stabilization, and disease modification in tafamidis treated transthyretin amyloid cardiomyopathy patients

Abstract Introduction Tafamidis inhibits progression of transthyretin (TTR) amyloid cardiomyopathy (ATTR-CM) by binding TTR tetramer and inhibiting its dissociation to monomers which can denature and result in amyloid fibril formation and deposition in cardiac tissue. Purpose While the phase 3 ATTR-ACT clinical data clearly demonstrated efficacy, quantification of TTR stabilization in patients and the degree to which the approved dose captures the full potential of the mechanism has yet to be assessed. Methods Isothermal titration calorimetry and subunit fraction exchange were used to determine affinities to the two binding sites on TTR. These values were used to develop a model of tafamidis binding to TTR in plasma that was applied to individual patient data to calculate TTR binding site occupancy and the change in total TTR levels induced by TTR stabilization. Population pharmacodynamic (PD) models were developed for three measures of disease progression, plasma NT-proBNP levels, Kansas City Cardiomyopathy Questionnaire – Overall Score (KCCQ-OS), and six-minute walk test (6MWT) distance, to evaluate patient response with the degree of TTR occupancy. Results In vitro binding data of wild-type TTR confirmed tafamidis binds two sites of TTR with negative cooperativity and provided precise estimates of the binding affinity to TTR and albumin. Modeling individual patient data of tafamidis exposure and increased TTR plasma levels using the in vitro derived binding affinity values confirms single site binding is consistent with complete tetramer stabilization. Patients given 80 mg tafamidis meglumine, the clinically approved dose for ATTR-CM, had a 92% reduction in unbound, unstabilized TTR, which correlated with a 53% decrease in NT-proBNP elevation, a 56% decrease in KCCQ-OS worsening and a 49% reduced decline in the 6MWT. For 100% receptor occupancy and stabilization, the expected effects on these measures are 58%, 61%, and 54% for NT-proBNP, KCCQ-OS, and 6MWT, respectively. Conclusions These results demonstrate a quantitative relationship between TTR stabilization, the mechanism of action of tafamidis, and accepted laboratory and patient-based outcomes in ATTR-CM. These results also support the value of TTR stabilization as a clinically beneficial treatment option which maintains the protein in its physiologically active form within the body. Funding Acknowledgement Type of funding sources: Private company. Main funding source(s): This study was sponsored by Pfizer.

Optimising the Nadroparin Dose for Thromboprophylaxis During Hemodialysis by Developing a Population Pharmacodynamic Model Using Anti-Xa Levels.

The optimal nadroparin dose in patients undergoing hemodialysis is difficult to determine in clinical practice. Anti-Xa levels ≥0.4 IU/mL and <2.0 IU/mL are suggested to prevent thrombus formation within the extracorporeal circuit whilst minimizing bleeding risk. We aimed to characterize the variability in the association between dose and anti-Xa levels, identify patient and dialysis characteristics that explained this variability, and optimize nadroparin dosing based on the identified characteristics. Anti-Xa samples were collected in patients who received intravenous nadroparin as thromboprophylaxis during routine dialysis sessions. A population pharmacodynamic model was developed using non-linear mixed-effects modelling. The percentage of patients ≥0.4 IU/mL (efficacy) and <2.0 IU/mL (safety) was simulated for different doses, patient and dialysis characteristics. Patients (n =137) were predominantly receiving standard hemodialysis (84.7% vs. hemodiafiltration 15.3%) and had a mean bodyweight of 76.3 kg (±16.9). Lean body mass (LBM), mode of dialysis, and dialyzer partially explained between-subject variability in anti-Xa levels. Patients on hemodiafiltration and those receiving hemodialysis with a high LBM (≥80 kg) had a low probability (<29%) of anti-Xa levels ≥0.4 IU/mL during the entire dialysis session. All patients, except hemodialysis patients with a low LBM (<50 kg), had a high probability (>70%) of peak anti-Xa levels <2.0 IU/mL. Mainly patients receiving hemodiafiltration and those receiving hemodialysis with a high LBM can benefit from a higher nadroparin dose than currently used in clinical practice, while having anti-Xa levels <2.0 IU/mL.