Limited blood sampling for pharmacokinetic dose tailoring of FVIII in the prophylactic treatment of haemophilia A

Effectiveness of PK-Guided Personalized Recombinant FVIII Treatment in Patients with Hemophilia A: Clinical Case Experiences Based on an Observational Study

Purpose

Prophylaxis with recombinant factor VIII (rFVIII) products is the gold-standard treatment for hemophilia A. However, interindividual differences affect the half-life and clearance of rFVIII products. The myPKFiT is a web-based medical-device software program for population pharmacokinetic (PK) simulation of FVIII products to guide accurate FVIII doses and dosing intervals. In this Japanese multicenter observational study, the efficacy of regimen adjustment using myPKFiT was examined.

Patients and Methods

Male patients with hemophilia A undergoing personalized treatment with myPKFiT using either octocog alfa or rurioctocog alfa pegol were included. Patients were aged <18 years. Primary endpoint was annualized bleeding rate (ABR). Secondary endpoints were ABR by type of bleeding, rFVIII product consumption, physical activity level, quality of life, and frequency of rFVIII administrations. Results are presented descriptively; however, for exploratory analysis, data before and after regimen adjustment were compared using the Wilcoxon signed-rank test.

Results

Seven patients aged 3-17 years (median age 13 years) participated in the study. Mean ABR for all bleeds decreased by 0.86 after PK-guided regimen adjustment. Four patients showed zero ABR before and after regimen adjustment using myPKFiT. No significant differences were noted in the consumption of rFVIII products. However, mean rFVIII consumption decreased in two patients after PK-guided regimen adjustment. Three patients increased physical activity and, according to the treatment based on the PK-guided regimen adjustment, this resulted in no increased bleeding.

Conclusion

The results from this study in a small number of patients suggest that PK-guided regimen adjustment with myPKFiT may support optimization of the individual prophylactic administration of the FVIII products octocog alfa and rurioctocog alfa pegol.

Study Registration

UMIN000044800.

How much prophylaxis is enough in haemophilia?

INTRODUCTION

Prophylaxis has become standard of care for all persons with haemophilia (PWH) with a severe phenotype. However, 'standard prophylaxis' with either factor or non-factor therapies (currently only emicizumab available) is prohibitively expensive for much of the world. We sought to address the question of 'How much prophylaxis is enough?' and 'Can it be individualized?' and specifically 'Can emicizumab be individualized?'.

METHODS

We reviewed the literature on prophylaxis in haemophilia since its inception in the 1950s to the present, the development of more and less intense factor prophylaxis regimens and their outcomes and additionally the published outcomes of prophylaxis with low dose emicizumab.

RESULTS

What these experiences collectively show is that low dose emicizumab does result in significant benefits to patients whilst being much less expensive than a "one size fits all" emicizumab prophylaxis approach. We also took note that some non-factor therapies still in development are individualized given that high doses of these can potentially put patients at risk.

CONCLUSIONS

Prophylaxis is now clearly accepted as standard of care for PWH with a severe phenotype but now in a very short time a large assortment of different treatment options for prophylaxis have become/are becoming available and the haemophilia community will need to determine how to best use these recognizing that no 'one treatment fits all'.

Predictive performance of pharmacokinetic-guided prophylactic dosing of factor concentrates in hemophilia A and B

Background

Pharmacokinetic (PK)-guided dosing is used to individualize factor (F)VIII and FIX replacement therapy.

Objectives

This study investigates the reliability and feasibility of PK-guided prophylactic dosing of factor concentrates in hemophilia A and B.

Methods

In this multicenter, prospective cohort study, people of all ages with hemophilia received prophylactic treatment with factor concentrates based on individual PK parameters. During follow-up, at least 4 measured FVIII/FIX levels per patient were compared with corresponding predicted levels obtained by Bayesian forecasting. Predictive performance was defined as adequate when ≥80% of measured FVIII/FIX levels were within ±25% of prediction (relative error). Additionally, mean absolute error and mean error were calculated. In post hoc analyses, predictive performance was assessed allowing maximum absolute errors of 1 (trough), 5 (mid), and 15 (peak) IU/dL. Five-point scale questionnaires addressed feasibility of PK guidance.

Results

We included 50 patients (median age, 19 years; range: 2-72 years). Median follow-up was 36 weeks. Seventy-one percent of levels (58% trough, 83% mid, and 80% peak) were within ±25% of prediction. Mean absolute errors were 0.8 (trough), 2.0 (mid), and 8.6 (peak) IU/dL. In post hoc analyses, 81% (trough), 96% (mid), and 82% (peak) of levels were within set limits. Patients reported low burden and high satisfaction.

Conclusion

PK-guided dosing was reliable according to post hoc analyses, based on low absolute errors that were regarded as clinically irrelevant in most cases. The predefined predictive performance was achieved in mid and peak factor levels but not in trough factor levels due to measurement inaccuracy. PK guidance also seemed feasible.

Development and internal validation of a clinical prediction model for individualized dosing of BAY 81-8973, A full-length recombinant factor VIII, in pediatric patients with haemophilia A

BACKGROUND

As the most commonly used coagulation factor VIII (FVIII) concentrate in China, the individualized dosing prediction model of Kovaltry (BAY81-8973) is not fully investigated in pediatric patients. The prophylaxis tailored by population pharmacokinetic (PopPK) model can optimize dosing regimens.

OBJECTIVES

This study aimed to develop PopPK models of BAY 81-8973 in pediatric patients, identify quantitative relationships of blood type (as a substitution for von Willebrand factor) on FVIII clearance and provide model-informed precision dosing (MIPD) procedures.

METHODS

Pediatric patients with severe hemophilia A were enrolled and PK tests were conducted. The blood samples were collected at six time point. One-stage-based activated partial thromboplastin time was used for FVIII activity. Basic demographics and key covariates (blood type and von Willebrand factor antigen) were collected. A nonlinear mixed-effect modeling (NONMEM) approach was employed to establish PopPK model. Simulations were performed to evaluate current dosing regimens and present MIPD strategies.

RESULTS

A total of 30 pediatric patients were included in the analysis. In the final model, Fat-free mass calculated from weight, age, and height was included as a size descriptor which affect FVIII apparent volume of distribution and clearance. Both von Willebrand factor antigen (VWF:Ag) and blood type accounted for the interindividual variability of FVIII clearance, but only one can retain in the final model. Therefore, two PopPK models based on VWF:Ag or blood type were developed. When the VWF:Ag value is doubled, the FVIII clearance is reduced by 35 %. Compared with blood type non-O, the clearance in pediatric patients with blood type O increased by 25.9 %. Weight-based dosing without regard to age and blood type resulted in large differences in FVIII trough activity. Patient demographics, dosing information, sparse blood samples and PopPK model together with Bayesian estimate constituted the MIPD workflow. Using it, the individual parameters and optimized dosing regimen could be achieved.

CONCLUSION

This is the first predictive model designed to predict individualized dosing of BAY 81-8973 in pediatric patients with Hemophilia A. These results are useful in the PK-guided prophylaxis among pediatric patients and hold great potential to improve their long-term clinical outcomes.

Effects of PK-guided prophylaxis on clinical outcomes and FVIII consumption for patients with moderate to severe Haemophilia A

INTRODUCTION

In recent years, there has been increased focus on individualizing treatment for persons with hemophilia including pharmacokinetic-guided (PK) dosing.

AIMS

In this retrospective study clinical outcomes before and after PK-guided prophylaxis were examined.

MATERIALS AND METHODS

Eight Haemophilia Treatment Centres from the United States participated in the study and included 132 patients classified into two cohorts: those undergoing a PK-assessment for product switch (switchers) or to optimize treatment (non-switchers). Subset analyses for the two most common products and patients with dosing per prescription label were included for annual bleeding rates (ABR), mean weekly consumption outcomes, and annualized cost of prophylaxis.

RESULTS

The most common products before and after index date were octocog alfa, rurioctocog alfa pegol, and efmoroctocog alfa. Seventy-four (56%) patients were identified as switchers and 58 (44%) patients were classified as non-switchers. The majority of patients (78.0%) experienced either a decrease in ABR post-index or maintained 0 ABR during pre- and post-index time periods, with similar proportions identified in both switchers (77.0%) and non-switchers (79.3%) populations. Non-switchers were identified as having no significant change in cost of therapy, while switchers experienced increased cost of therapy driven by higher price of extended half-life products. Within subset analyses, patients receiving rurioctocog alfa pegol and efmoroctocog alfa had mean ABR under 1 after index date.

CONCLUSION

PK-guided prophylaxis has the potential to improve clinical outcomes without increase in cost of therapy for patients maintaining product and can aid in maintaining effective protection against bleeds in those switching product.

A personalized limited sampling approach to better estimate terminal half-life of FVIII concentrates

INTRODUCTION

Hemophilia A is a bleeding disorder characterized by a deficiency of a coagulation factor VIII and optimally treated using pharmacokinetics (PK)-guided prophylactic replacement therapy. To decrease patient burden, PK can be estimated from sparse sampling leveraging population PK modeling. However, recommendations for sampling times meant for patients with hemophilia A as a group may not be optimal at the individual level.

OBJECTIVE

To evaluate a personalized limited sampling approach (Personalized LSA) that suggests a next sampling time point that would provide a more accurate estimation of terminal half-life of FVIII concentrates when using a population PK approach.

METHODS

331 PK studies with rich sampling were extracted from the WAPPS-Hemo database. Two sampling approaches were evaluated and compared: 974 PK studies consisting of two samples were built from the rich sampling data including one sample selected using the personalized LSA prediction; 974 PK studies consisting of two samples were built from the rich sampling data including one sample selected randomly. Half-life values were estimated on the sparse data and compared within patients to the estimates obtained on the rich data for assessing the error on half-life values.

RESULTS

Relative errors between estimates from sparse sampling data using personalized LSA and from rich sampling data were always lower than 20% and significantly lower than the comparative approach that used random sampling (median-95th percentile were 3.8%-13.1% vs. 7.0%-23.5%, respectively, p-value < 10-10 ). Moreover, less than 4% of the samples suggested by the personalized LSA were below the limit of quantification.

CONCLUSIONS

Identifying the most informative sampling points for PK assessment using a Personalized LSA approach that accounts for individual differences in PK improves the precision of FVIII terminal half-life estimates in sparse sampling.

Pharmacokinetic profile of children with haemophilia A receiving low-dose FVIII prophylaxis in Indonesia: A single centre experience

BACKGROUND

Pharmacokinetic (PK) studies of low-dose prophylaxis (LDP) of coagulation factor VIII (FVIII) in children with severe haemophilia A (SHA) are scarce.

OBJECTIVE

This study aims to investigate the PK profile of children with SHA receiving LDP of FVIII.

METHODS

Paediatric patients receiving FVIII infusions (10 IU/kg twice weekly) were included. PK profiles were estimated using the Web Accessible Population Pharmacokinetic Service for Haemophilia (WAPPS-Haemo). The primary outcomes were the terminal half-life (t_1/2 ), concentration-time profile, and time to reach an FVIII level of < 1%. The secondary outcome was the suggested dosing interval of FVIII prophylaxis based on the individual PK profile.

RESULTS

Twenty-five patients were recruited; their mean age was 12.3 ± 3.0 years. The t_1/2 differed among patients receiving LDP of FVIII twice weekly, with a median of t_1/2 was 14.8 h (IQR 12.6-16). The median time to reach an FVIII level of < 1% was 73.8 h (IQR 58.8-80.3). Most patients could maintain a trough level of FVIII > 1% longer than 48 h. At 72-96 h, patients needed a second dose of FVIII infusion because the FVIII level was < 1%. The suggested dosing interval of FVIII prophylaxis ranged from daily to every 96 h, depending on the individual PK profile.

CONCLUSION

Our study identified inter-individual differences in the PK parameters using LDP of FVIII twice weekly. The inter-individual results in different dosing intervals advise the timing of LDP. Estimating individual PK parameters enables the identification of the optimal prophylaxis frequency to prevent bleedings.

External qualification of the Web-Accessible Population Pharmacokinetic Service-Hemophilia (WAPPS-Hemo) models for octocog alfa using real patient data

BACKGROUND

Existing adult patient pharmacokinetic (PK) data from the published Advate vs Kovaltry PK crossover study were used for this validation study. This data set is appropriate for qualification, given that it has not been previously submitted to Web-Accessible Population Pharmacokinetic Service-Hemophilia (WAPPS-Hemo) and will not have impacted the WAPPS-Hemo models for Kovaltry.

OBJECTIVE

To compare the population PK parameters for Kovaltry (BAY 81-8973) derived from the WAPPS-Hemo models with PK parameters derived from noncompartmental analysis (NCA), using a validation PK dataset.

METHODS

The qualification data set included Kovaltry factor activity (10 samples per infusion) and anthropometric data for 18 patients. Two analyses were performed comparison of Bayesian forecasting from the WAPPS-Hemo models versus NCA using the full 10-sample data set; and comparison of Bayesian forecasting using the full versus reduced 4- and 3-sample data sets. Agreement between outcomes was assessed by quantifying the variability and bias of the error.

RESULTS

Comparison of WAPPS-Hemo models versus NCA led to well-correlated outcomes despite a systematic overprediction of clearance. Population PK models demonstrated greater consistency with NCA on one-stage data, compared with chromogenic data. WAPPS-Hemo model results were consistent in reduced sampling compared to full sampling. Inclusion of a 48-hour time point in the reduced sampling greatly improved the consistency with full sampling.

DISCUSSION

Qualification of population PK models and their use for Bayesian forecasting in full and reduced sampling is an essential step toward their validation. The evaluations performed in this study support the confidence of PK parameter estimates provided by the models.

Favorable Pharmacokinetic Characteristics of Extended-Half-Life Recombinant Factor VIII BAY 94-9027 Enable Robust Individual Profiling Using a Population Pharmacokinetic Approach

Background

Prophylaxis with factor VIII (FVIII) should be individualized based on patient characteristics, including FVIII pharmacokinetics. Population pharmacokinetic (popPK) modeling simplifies pharmacokinetic studies by obviating the need for multiple samples.

Objective

The objective of this study was to characterize the pharmacokinetics and inter-individual variability (IIV) of BAY 94-9027 in relation to patient characteristics in support of a popPK-tailored approach, including identifying the optimal number and timing of pharmacokinetic samples.

Methods

Pharmacokinetic samples from 198 males (aged 2‒62 years) with severe hemophilia A, enrolled in BAY 94-9027 clinical trials, were analyzed. Baseline age, height, weight, body mass index, lean body weight (LBW), von Willebrand factor (VWF) level, and race were evaluated. A popPK model was developed and used to simulate pharmacokinetic endpoints difficult to observe from measured FVIII levels, including time to maintain FVIII levels above 1, 3, and 5 IU/dL after different BAY 94-9027 doses.

Results

A one-compartment model adequately described BAY 94-9027 pharmacokinetics. Clearance and central volume of distribution were significantly associated with LBW; clearance was inversely correlated with VWF. Due to the monophasic pharmacokinetics and well-understood IIV sources, identification of patient pharmacokinetics was achievable with sparse blood sampling. Median predicted time to maintain FVIII levels > 1 IU/dL in patients aged ≥ 12 years ranged from 120.1 to 127.2 h after single BAY 94-9027 doses of 45‒60 IU/kg.

Conclusions

This analysis evaluated the pharmacokinetics of BAY 94-9027 and its sources of IIV. Using the model, determination of individual patient pharmacokinetics was possible with few FVIII samples, and a sparse sampling design to support pharmacokinetic-guided dosing was identified.

Pharmacokinetics of perioperative FVIII in adult patients with haemophilia A: An external validation and development of an alternative population pharmacokinetic model

INTRODUCTION

Haemophilia A patients require perioperative clotting factor replacement to limit excessive bleeding. Weight-based dosing of Factor VIII (FVIII) does not account for inter-individual pharmacokinetic (PK) variability, and may lead to suboptimal FVIII exposure.

AIM

To perform an external validation of a previously developed population PK (popPK) model of perioperative FVIII in haemophilia A patients.

METHODS

A retrospective chart review identified perioperative haemophilia A patients at the University of North Carolina (UNC) between April 2014 and November 2019. Patient data was used to externally validate a previously published popPK model proposed by Hazendonk. Based on these validation results, a modified popPK model was developed to characterize FVIII PK in our patients. Dosing simulations were performed using this model to compare FVIII target attainment between intermittent bolus (IB) and continuous infusion (CI) administration methods.

RESULTS

A total of 521 FVIII concentrations, drawn from 34 patients, were analysed. Validation analyses revealed that the Hazendonk model did not fully capture FVIII PK in the UNC cohort. Therefore, a modified one-compartment model, with weight and age as covariates on clearance (CL), was developed. Dosing simulations revealed that CI resulted in improved target attainment by 16%, with reduced overall FVIII usage by 58 IU/kg, compared to IB.

CONCLUSION

External validation revealed a previously published popPK model of FVIII did not adequately characterize UNC patients, likely due to differences in patient populations. Future prospective studies are needed to evaluate our model prior to implementation into clinical practice.

Terminal half-life of FVIII and FIX according to age, blood group and concentrate type: Data from the WAPPS database

BACKGROUND

Real-life data on pharmacokinetics of factor (F) VIII/IX concentrates, especially extended half-life (EHL), concentrates in large cohorts of persons with hemophilia are currently lacking.

OBJECTIVES

This cross-sectional study aimed to establish reference values for terminal half-life (THL) for FVIII/IX concentrates according to concentrate type, age, blood group and inhibitor history.

PATIENTS/METHODS

Data were extracted from the Web-Accessible Population Pharmacokinetics Service database. Groups were compared by nonparametric tests. THL was modelled according to patient characteristics and concentrate type.

RESULTS

Infusion data (n = 8022) were collected from 4832 subjects (including 2222 children) with severe hemophilia (age: 1 month-85 years; 89% hemophilia A; 34% using EHL concentrates, 9.8% with history of inhibitors). THL of FVIII-EHL was longer than of FVIII standard half-life (SHL; median 15.1 vs. 11.1 h). FVIII-THL was dependent on age, concentrate type, blood group, and inhibitor history. THL of FIX-EHL was longer than of FIX-SHL (median 106.9 vs. 36.5 h). FIX-THL increased with age until 30 years and remained stable thereafter. FVIII-THL was shorter in subjects with blood group O. THL was decreased by 1.3 h for FVIII and 22 h for FIX in subjects with a positive inhibitor history.

CONCLUSIONS

We established reference values for FVIII/IX concentrates according to patient characteristics and concentrate type in a large database of hemophilia patients. These reference values may inform clinical practice (e.g., assessment of immune tolerance success), economic implications of procurement processes and value attribution of novel treatments (e.g., mimetics, gene therapy).

Pharmacokinetics and complementary evaluation system-based guidance on prophylaxis of paediatric patients with haemophilia A in China with Kovaltry: protocol of the LEAP study

INTRODUCTION

Haemophilia A is a rare inherited bleeding disease caused by the deficiency of coagulation factor VIII (FVIII). The main treatment protocol is to administer regular exogenous FVIII concentrate infusions. With the discovery of variability in individualised pharmacokinetics (PK) and bleeding phenotype, the previous weight-based approach needs to be replaced by more advanced PK-tailored prophylaxis with an accurate evaluation system. In this study, we combine individualised PK profiles and a complementary evaluation system to guide prophylaxis in paediatric patients with haemophilia A.

METHODS AND ANALYSIS

This is a single-centre, prospective single-arm study. The aim of this study is to assess the effectiveness of a new strategy combining PK and a complementary evaluation system to treat haemophilia A in Chinese paediatric patients. Sixty paediatric patients with haemophilia will be recruited. After PK testing, they will receive a PK-guided stepup prophylaxis in the next 2 years. The dosing regimen will be determined according to individualised PK profiles and complementary evaluation findings. Related indicators at the end of the study will be compared with the values at treatment initiation to examine the effectiveness of this new strategy. The demographic data of the investigated patients will be summarised by descriptive statistics. Quantitative data will be described by summary statistics, including arithmetic median, range, mean and arithmetic SD. Analyses will use t-test to compare indicators such as bleeding rate and imaging score at both ends of the study as well as during follow-up.

ETHICS AND DISSEMINATION

The study has been approved by the Ethics Committee of Beijing Children's Hospital (Number 2020-Z-095). The findings will be presented at international meetings such as World Federation of Hemophilia World Congress. Related manuscripts will be submitted to peer-review journals such as Blood and Hemophilia.

TRIAL REGISTRATION NUMBER

ChiCTR2000037821; Pre-results.

Low-dose immune tolerance induction alone or with immunosuppressants according to prognostic risk factors in Chinese children with hemophilia A inhibitors

BACKGROUND

In developing countries, children with hemophilia A (HA) with high-titer inhibitor and poor immune tolerance induction (ITI) prognostic risk(s) cannot afford the recommended high- or intermediate-dose ITI.

OBJECTIVES

To determine the efficacy of low-dose ITI (plasma-derived factor VIII [FVIII]/von Willebrand factor at 50 FVIII IU/kg every other day) by itself (ITI-alone) or combined with immunosuppressants rituximab and prednisone (ITI-IS) in children with HA with high-titer inhibitor.

METHODS

All enrolled patients had pre-ITI inhibitor ≥10 BU. We used ITI-alone if inhibitor titer was <40 BU pre-ITI and during ITI, and ITI-IS if titer was ≥100 BU (historic) or ≥40 BU (pre- or during ITI) or if the patient was nonresponsive on ITI-alone.

RESULTS

Fifty-six children were analyzable, with median historic peak inhibitor titer 48.0 BU and followed for median 31.4 months. Overall, 35 (62.5%) achieved phase 2 success with negative inhibitor and normal FVIII recovery. The phase 2 success rate was 95% for the 20 patients receiving ITI-alone. For the 36 patients receiving ITI-IS, the phase 2 success rate was 44.4%, but would increase to 63.6% if the 14 patients with historic peak inhibitor titer ≥100 BU (and having phase 2 success rate of only 14.3%) were excluded. One patient developed repeated infection after IS treatment. Relapse occurred in 11.4% (4/35) patients with phase 2 success associated with rapid ITI dose reduction or irregular post-ITI FVIII prophylaxis. Our strategy reduced the cost from high-dose ITI by 74% to 90%.

CONCLUSION

The use of low-dose ITI with or without immunosuppressants according to ITI prognostic risk(s) is a clinically and economically feasible strategy for eradicating inhibitors in children with HA, particularly for those with historic peak inhibitor titer <100 BU.

Haemophilia

Haemophilia A and B are rare congenital, recessive X-linked disorders caused by lack or deficiency of clotting factor VIII (FVIII) or IX (FIX), respectively. The severity of the disease depends on the reduction of levels of FVIII or FIX, which are determined by the type of the causative mutation in the genes encoding the factors (F8 and F9, respectively). The hallmark clinical characteristic, especially in untreated severe forms, is bleeding (spontaneous or after trauma) into major joints such as ankles, knees and elbows, which can result in the development of arthropathy. Intracranial bleeds and bleeds into internal organs may be life-threatening. The median life expectancy was ~30 years until the 1960s, but improved understanding of the disorder and development of efficacious therapy based on prophylactic replacement of the missing factor has caused a paradigm shift, and today individuals with haemophilia can look forward to a virtually normal life expectancy and quality of life. Nevertheless, the potential development of inhibitory antibodies to infused factor is still a major hurdle to overcome in a substantial proportion of patients. Finally, gene therapy for both types of haemophilia has progressed remarkably and could soon become a reality.

Development and Validation of a Population-Pharmacokinetic Model for Rurioctacog Alfa Pegol (Adynovate®): A Report on Behalf of the WAPPS-Hemo Investigators Ad Hoc Subgroup

BACKGROUND AND OBJECTIVE

Rurioctacog alfa pegol (Adynovate) is a modified recombinant factor VIII concentrate used for treating hemophilia A. Aiming to improve treatment tailoring on the Web-Accessible Population Pharmacokinetic Service-Hemophilia (WAPPS-Hemo) platform for patients of all ages treated with Adynovate, we have developed and evaluated a population pharmacokinetic (PopPK) model. On the platform, PopPK models are used as priors for Bayesian forecasting that derive individual PK of hemophilia patients and are subsequently used for personalized dose regimen design.

METHODS

Factor activity measurements and demographic covariate data from patients infused with Adynovate were extracted from the WAPPS-Hemo database. Evaluations testing the appropriateness of Bayesian forecasting included 10-fold cross validation, a limited sampling analysis (LSA), and an external evaluation using additional independent data extracted from the WAPPS-Hemo database at a later date.

RESULTS

The model was constructed using 650 plasma factor activity observations (555 one stage assay and 95 chromogenic assay - 4.6% below limit of quantification) measured in 154 patients from 36 hemophilia centres. A two-compartment model including between subject variability on clearance and central volume was selected as the base model. Covariates were fat free mass on clearance and central volume, age on clearance and assay type on activity. The final model was well-suited to predict PK parameters of new individuals (n = 26) from sparse observations.

CONCLUSIONS

The development of a PopPK model for Adynovate using real-world data increases the covariate space (e.g. age) beyond what is possible from clinical trial data. This model is available on the WAPPS-Hemo platform for tailoring treatment in hemophilia A patients.

Limited sampling strategies for accurate determination of extended half-life factor VIII pharmacokinetics in severe haemophilia A patients

BACKGROUND

Extended half-life (EHL) factor VIII (FVIII) products may decrease the burden of prophylactic treatment in haemophilia A by reducing infusion frequency. However, these products still exhibit wide inter-patient variability and benefit from pharmacokinetic (PK) tailoring.

OBJECTIVE

Identify limited sampling strategies for rFVIIIFc, an EHL FVIII product, that produce accurate estimates of PK parameters and relevant troughs.

METHODS

We performed a limited sampling analysis on simulated populations of adults, adolescents, and children based on published population PK data. Sampling strategies were evaluated by comparing the error in estimates of half-life, clearance, and trough levels, to a full 6-sample design. Furthermore, we assessed the impact of incorporating knowledge about prior doses, and the day of the PK study within the regimen. We also evaluated the potential inappropriate dose adjustment rate (IDAR) among the modelled sampling strategies.

RESULTS

Many sampling strategies, including several 2-sample designs, accurately predicted the PK and exposure measures (median absolute error <10%). When samples are only collected during a single visit (i.e., predose + peak), inclusion of prior dose information reduces median half-life error from >20% to ~5% for adults/adolescents. In this same scenario, appropriate scheduling of the PK study decreases likelihood of unmeasurable predose samples, reducing median error on the 72-h trough from 25% to <12% in the youngest population.

CONCLUSIONS

The PK of rFVIIIFc can be accurately estimated using only peak and trough samples, provided that knowledge of prior doses is incorporated and the PK study is planned on an appropriate day within the dosing regimen.

Population Pharmacokinetic Analysis of Recombinant Factor VIII Fc Fusion Protein in Subjects With Severe Hemophilia A: Expanded to Include Pediatric Subjects

Recombinant factor VIII Fc fusion protein (rFVIIIFc) has been indicated for adults and children with hemophilia A. The objective of this article was to build a population pharmacokinetic (PK) model using adult and pediatric data sets and explore relevant dosing scenarios across all ages. The activity-time profiles of rFVIIIFc from 3 clinical studies (all trials registered at https://www.clinicaltrials.gov: NCT01027377, NCT01181128, and NCT01458106) were characterized, and covariates that determine variability of rFVIIIFc PK in children and adults were identified and implemented. Data sets were pooled to estimate population PK parameters. Simulations were conducted to generate activity-time profiles at steady state (SS). The proportion of subjects maintaining SS trough >1 and >3 IU/dL and time >10 IU/dL were estimated. The rFVIIIFc model was a two-compartment model that identified weight and von Willebrand factor as significant covariates. Model-predicted SS peaks and troughs of rFVIIIFc activity-time profiles confirmed the necessity of modifying dosing in pediatric subjects. The model also predicted that the average subject in the adult and adolescent group dosed with 40 IU/kg every 2 days maintained factor VIII activity >10 IU/dL for the entire duration. Children aged <6 years and aged 6 to <12 years receiving this dose maintained factor VIII activity of >10 IU/dL for nearly two-thirds and three-quarters of their time, respectively. In conclusion, these population PK analyses characterize activity-time profiles for rFVIIIFc among pediatric and adult subjects. The model was used for simulation of clinically relevant dosing scenarios, which can provide better protection and better clinical outcomes.

Impact of extreme weight loss on factor VIII concentrate pharmacokinetics in haemophilia

We explored the effects of extreme weight loss after gastric bypass surgery on factor VIII concentrate pharmacokinetic (PK) parameters in a patient with haemophilia A. We present a 32-year-old man with severe haemophilia A, with a body mass index (BMI) of 42.6 kg/m² who underwent laparoscopic sleeve gastrectomy. We showed that a population PK model with ideal body weight as morphometric variable instead of bodyweight led to an adequate description of the individual PKs in this patient with a variable BMI. Strikingly, no differences were observed in the individual PK parameters after extreme weight loss. Therefore, the resulting extreme weight loss after surgery did not lead to prophylactic dose changes in this patient with severe haemophilia. We carefully conclude that population PK-pharmacodynamic models are still obligatory to give more insight into functional effects of significant weight loss on the haemostatic balance.

A comparison of MyPKFiT and WAPPS-Hemo as dosing tools for optimizing prophylaxis in patients with severe haemophilia A treated with Octocog alfa

INTRODUCTION

MyPKFiT and the Web-Accessible Population Pharmacokinetic service-Hemophilia (WAPPS-Hemo) are web-based population-based applications developed for helping physicians individualize and optimize replacement therapy. Although MyPKFiT is intended for Octocog alfa and Rurioctocog alfa pegol use only, the WAPPS-Hemo is applicable to all factor VIII concentrates.

AIM

To compare MyPKFiT and WAPPS-Hemo as dosing tools for optimizing treatment of patients with severe haemophilia A on regular prophylaxis with Octocog alfa in a real-world setting.

METHODS

Fourteen patients with severe haemophilia A (median age 30.8 years; range 20-71) were enrolled. The FVIII activity was measured twice after a regular dose of Octocog alfa by the chromogenic and the one-stage assays. PK analyses were performed using each tool and dosing estimations to reach trough levels of 1%, 3% or 5% after 48 h. Findings were calculated and compared.

RESULTS

The two PK algorithms yielded similar t½ independent of the type of FVIII assay used. However, there were significant differences in the time to reach 1%, 3% and 5%. The WAPPS-Hemo generated 10-12 h longer time to a trough of 1% and up to 4 h for the troughs of 3% and 5%. Accordingly, the doses estimated by WAPPS-Hemo for a daily regimen were between 28% and 100% of those proposed by MyPKFiT.

CONCLUSIONS

MyPKFiT and WAPPS-Hemo provided similar half-life estimations for Octocog alfa independent of the FVIII assay used. The doses suggested by WAPPS-Hemo to reach specific troughs were overall lower, which may have implications for treatment optimization.

Extended half-life factor VIII concentrates in adults with hemophilia A: Comparative pharmacokinetics of two products

BACKGROUND

The use of pharmacokinetic (PK) studies to help design personalized prophylaxis regimens for factor VIII (FVIII) concentrate in individuals with hemophilia A has been recognized for many years but only became practical for routine clinical use with the availability of web-accessible population PK applications based on Bayesian analysis.

OBJECTIVE

To compare PK variables using population PK studies done on 2 extended half-life recombinant FVIII concentrates in 23 individuals with hemophilia A after switching from one product to the other.

METHODS

We retrospectively analyzed PK parameters derived from the Web-Accessible Population Pharmacokinetic Service-Hemophilia (WAPPS-HEMO) application on 23 individuals with severe or moderately severe hemophilia A who were required to switch from recombinant FVIII Fc (Eloctate; Biogen, Cambridge, MA, USA) to recombinant antihemophilic factor PEGylated (Adynovate; Takeda Pharmaceutical Company, Osaka, Japan) between 2016 and 2017.

RESULTS

There were minor PK differences between Eloctate and Adynovate, but some parameters did reach statistical significance, namely in vivo recovery (mean, 2.73 IU/dL per IU/kg vs 2.41 IU/dL per IU/kg), clearance (mean, 0.163 mL/h vs 0.194 mL/h), and volume of distribution at steady state (mean, 42.5 ml/kg vs 49.8 mL/kg). Smaller nonsignificant trends toward higher values for Adynovate were seen in terminal half-life, area under the curve, and predicted times to 5% and 1% residual FVIII after infusion.

CONCLUSION

Population PK analysis revealed differences between the two extended half-life FVIII concentrates, reaching significance for in vivo recovery, clearance, and volume of distribution.

Model-Based Evaluation of Linear Limited and Bayesian Sparse Sampling for Therapeutic Monitoring of Recombinant Coagulation Factor IX

Dosing of coagulation factor products is mainly determined based on a patient's body weight; however, several studies have reported high interindividual variability in their pharmacokinetics (PK). The objective of this study was to develop and evaluate 2 sparse sampling methods for the estimation of AUC of recombinant factor IX (BeneFIX) as proof of concept for dose individualization. A population pharmacokinetic model was used to generate the plasma factor IX activity-versus-time data. The linear limited sampling model (LLSM) was developed based on the correlation of factor IX activity versus AUC_0-72 hours following screening of several blood sampling times in adolescent and adult subjects (n = 90 subjects). Factor IX trough concentrations were predicted from a relationship established from AUC versus factor IX activity measured 72 hours postdosing. Using the best selected sampling time, the LLSM and Bayesian model were validated in separate data sets (n = 75 subjects). Using the LLSM and Bayesian analysis, a blood sample at 24 hours predicted AUC with bias and root mean square error < 5% and < 15%, respectively. The predicted trough concentrations were ≥1 IU/dL in 99% and 100% of subjects by the LLSM and Bayesian model, respectively. The average factor IX dose for a target AUC of 800 IU·h/dL was 61, 60, and 63 IU/kg using the extensive (reference), LLSM and Bayesian model, respectively. Overall, the AUC, trough concentrations and individualized dosing of recombinant factor IX could be reasonably predicted using the LLSM and Bayesian model.

Precision Dosing Priority Criteria: Drug, Disease, and Patient Population Variables

The administered dose of a drug modulates whether patients will experience optimal effectiveness, toxicity including death, or no effect at all. Dosing is particularly important for diseases and/or drugs where the drug can decrease severe morbidity or prolong life. Likewise, dosing is important where the drug can cause death or severe morbidity. Since we believe there are many examples where more precise dosing could benefit patients, it is worthwhile to consider how to prioritize drug-disease targets. One key consideration is the quality of information available from which more precise dosing recommendations can be constructed. When a new more precise dosing scheme is created and differs significantly from the approved label, it is important to consider the level of proof necessary to either change the label and/or change clinical practice. The cost and effort needed to provide this proof should also be considered in prioritizing drug-disease precision dosing targets. Although precision dosing is being promoted and has great promise, it is underutilized in many drugs and disease states. Therefore, we believe it is important to consider how more precise dosing is going to be delivered to high priority patients in a timely manner. If better dosing schemes do not change clinical practice resulting in better patient outcomes, then what is the use? This review paper discusses variables to consider when prioritizing precision dosing candidates while highlighting key examples of precision dosing that have been successfully used to improve patient care.

Clinical application of Web Accessible Population Pharmacokinetic Service-Hemophilia (WAPPS-Hemo): Patterns of blood sampling and patient characteristics among clinician users

BACKGROUND

Use of population pharmacokinetics (PopPK) to facilitate PK-informed prophylaxis in clinical practice has gained momentum among haemophilia providers due to the accessibility of tools such as the Web Accessible Population Pharmacokinetic Service-Hemophilia (WAPPS-Hemo) and availability of extended half-life (EHL) factor concentrates. It is unknown how clinicians implement PopPK.

AIM

To investigate the evolution of PopPK use in clinical practice by comparing blood sampling strategies, patient features, and factor group between initial and recent periods of WAPPS-Hemo availability.

METHODS

PK data for haemophilia A and haemophilia B patients from two time periods were extracted from the WAPPS-Hemo database: early availability (10/2015-09/2016) and recent use (10/2017-09/2018). We compared patient characteristics (age, body weight, haemophilia type), product type and dose, and blood sampling times between the time frames.

RESULTS

Over 1900 eligible infusions were submitted to WAPPS-Hemo during the periods studied, with 85% representing FVIII concentrates. In the recent cohort, PK profiles were requested for younger patients (median age 18 vs 26 years), with increased proportional EHL FVIII use (29% vs 14% of infusions). High-use centres generally submitted fewer blood samples per infusion than non-high-use centres, although the number of samples collected by non-high-use centres decreased significantly over time. During both periods, blood sample timing was generally consistent with ISTH recommended windows.

CONCLUSION

The use of WAPPS-Hemo by haemophilia providers grew by over threefold between the time periods investigated. While sampling times have included key time points proposed first by Björkman since early WAPPS-Hemo usage, a trend towards minimizing sampling was observed.

Routine clinical care data for population pharmacokinetic modeling: the case for Fanhdi/Alphanate in hemophilia A patients

Fanhdi/Alphanate is a plasma derived factor VIII concentrate used for treating hemophilia A, for which there has not been any dedicated model describing its pharmacokinetics (PK). A population PK model was developed using data extracted from the Web-Accessible Population Pharmacokinetic Service-Hemophilia (WAPPS-Hemo) project. WAPPS-Hemo provided individual PK profiles for hemophilia patients using sparse observations as provided in routine clinical care by hemophilia centers. Plasma factor activity measurements and covariate data from hemophilia A patients on Fanhdi/Alphanate were extracted from the WAPPS-Hemo database. A population PK model was developed using NONMEM and evaluated for suitability for Bayesian forecasting using prediction-corrected visual predictive check (pcVPC), cross validation, limited sampling analysis and external evaluation against a population PK model developed on rich sampling data. Plasma factor activity measurements from 92 patients from 12 centers were used to derive the model. The PK was best described by a 2-compartment model including between subject variability on clearance and central volume, fat free mass as a covariate on clearance, central and peripheral volumes, and age as covariate on clearance. Evaluations showed that the developed population PK model could predict the PK parameters of new individuals based on limited sampling analysis and cross and external evaluations with acceptable precision and bias. This study shows the feasibility of using real-world data for the development of a population PK model. Evaluation and comparison of the model for Bayesian forecasting resulted in similar results as a model developed using rich sampling data.

Handling interoccasion variability in model-based dose individualization using therapeutic drug monitoring data

AIMS

This study aims to assess approaches to handle interoccasion variability (IOV) in a model-based therapeutic drug monitoring (TDM) context, using a population pharmacokinetic model of coagulation factor VIII as example.

METHODS

We assessed 5 model-based TDM approaches: empirical Bayes estimates (EBEs) from a model including IOV, with individualized doses calculated based on individual parameters either (i) including or (ii) excluding variability related to IOV; and EBEs from a model excluding IOV by (iii) setting IOV to zero, (iv) summing variances of interindividual variability (IIV) and IOV into a single IIV term, or (v) re-estimating the model without IOV. The impact of varying IOV magnitudes (0-50%) and number of occasions/observations was explored. The approaches were compared with conventional weight-based dosing. Predictive performance was assessed with the prediction error percentiles.

RESULTS

When IOV was lower than IIV, the accuracy was good for all approaches (50^th percentile of the prediction error [P50] <7.4%), but the precision varied substantially between IOV magnitudes (P97.5 61-528%). Approach (ii) was the most precise forecasting method across a wide range of scenarios, particularly in case of sparse sampling or high magnitudes of IOV. Weight-based dosing led to less precise predictions than the model-based TDM approaches in most scenarios.

CONCLUSIONS

Based on the studied scenarios and theoretical expectations, the best approach to handle IOV in model-based dose individualization is to include IOV in the generation of the EBEs but exclude the portion of unexplained variability related to IOV in the individual parameters used to calculate the future dose.

Desmopressin treatment combined with clotting factor VIII concentrates in patients with non-severe haemophilia A: protocol for a multicentre single-armed trial, the DAVID study

INTRODUCTION

Haemophilia A is an inherited bleeding disorder characterised by factor VIII (FVIII) deficiency. In patients with non-severe haemophilia A, surgery and bleeding are the main indications for treatment with FVIII concentrate. A recent study reported that standard dosing frequently results in FVIII levels (FVIII:C) below or above FVIII target ranges, leading to respectively a bleeding risk or excessive costs. In addition, FVIII concentrate treatment carries a risk of development of neutralising antibodies. An alternative is desmopressin, which releases endogenous FVIII and von Willebrand factor. In most patients with non-severe haemophilia A, desmopressin alone is not enough to achieve FVIII target levels during surgery or bleeding. We hypothesise that combined pharmacokinetic (PK)-guided administration of desmopressin and FVIII concentrate may improve dosing accuracy and reduces FVIII concentrate consumption.

METHODS AND ANALYSIS

In the DAVID study, 50 patients with non-severe haemophilia A (FVIII:C ≥0.01 IU/mL) with a bleeding episode or undergoing surgery will receive desmopressin and FVIII concentrate combination treatment. The necessary dose of FVIII concentrate to reach FVIII target levels after desmopressin administration will be calculated with a population PK model. The primary endpoint is the proportion of patients reaching FVIII target levels during the first 72 hours after start of the combination treatment. This approach was successfully tested in one pilot patient who received perioperative combination treatment.

ETHICS AND DISSEMINATION

The DAVID study was approved by the medical ethics committee of the Erasmus MC. Results of the study will be communicated trough publication in international scientific journals and presentation at (inter)national conferences.

TRIAL REGISTRATION NUMBER

NTR5383; Pre-results.

Dose tailoring of human cell line-derived recombinant factor VIII simoctocog alfa: Using a limited sampling strategy in patients with severe haemophilia A

AIMS

The use of factor VIII (FVIII) prophylaxis in haemophilia A is considered the standard of care, particularly in children. Despite adjustment of doses for body weight and/or age, a large pharmacokinetic (PK) variability between patients has been observed. PK-tailored prophylaxis may help clinicians adjust coagulation factor FVIII activity (FVIII:C) to the desired level, which may differ in individual patients. The objective was to develop a population PK model for simoctocog alfa based on pooled clinical trial data and to develop a Bayesian estimator to allow PK parameters in individual patients to be estimated using a reduced number of blood samples.

METHODS

PK data from 86 adults and 29 children/adolescents with severe haemophilia A were analysed. The FVIII data measured using 2 different assays (chromogenic and the 1-stage clotting assay) were fit to separate develop population PK models using nonlinear mixed-effect models. A Bayesian estimator was then developed to estimate the time above the threshold of 1%.

RESULTS

The PK data for chromogenic and the 1-stage clotting assays were both best described by a 2-compartment models. Simulations demonstrated good predictive capacity. The limited sampling strategy using blood sample at 3 and 24 hours allowed an accurate estimation of the time above the threshold of 1% FVIII:C (mean bias 0.01 and 0.11, mean precision 0.18 and 0.45 for 2 assay methods).

CONCLUSION

In this study, we demonstrated that a Bayesian approach can help to reduce the number of samples required to estimate the time above the threshold of 1% FVIII:C with good accuracy.

Pharmacokinetic Studies of Factor VIII in Chinese Boys with Severe Hemophilia A: A Single-Center Study

Background:

Although much attention has been paid to the pharmacokinetics (PKs) of different factor VIII (FVIII) concentrates in persons with hemophilia A (HA), limited information is available in young boys with severe HA. In this study, we aimed to assess the PK parameters of FVIII products in boys with severe HA in China.

Methods:

A total of 36 boys (plasma-derived [pd]-FVIII, n = 15; recombinant [r] FVIII, n = 21) were enrolled between January 2015 and May 2016 in Beijing Children's Hospital. PK characteristics of FVIII products were studied according to a reduced 4-sampling time point design (1 h, 9 h, 24 h, and 48 h postinfusion).

Results:

The mean FVIII half-life (t_1/2) was 10.99 ± 3.45 h (range 5.52–20.02 h), the mean in vivo recovery (IVR) was 2.01 ± 0.42 IU/dl per IU/kg (range 1.24–3.02 IU/dl per IU/kg) and mean clearance (CL) of FVIII is 4.34 ± 1.58 ml·kg⁻¹·h⁻¹ (range 2.29–7.90 ml·kg⁻¹·h⁻¹). We also analyzed the influence of several parameters that potentially modulate FVIII PK. The age was closely associated with FVIII half-life (R²= 0.32, P < 0.01). The t_1/2 of FVIII increased by 0.59 h per year. Besides age, von Willebrand factor antigen (VWF:Ag) also was associated with FVIII half-life (R²= 0.52, P < 0.01). Patients with blood Group O had a shorter FVIII half-life than patients with non-O blood group (9.40 ± 0.68 h vs. 12.3 ± 0.79 h, t = 2.70, P = 0.01). The FVIII IVR correlated with age (R²= 0.21, P < 0.01) and VWF:Ag level (R²= 0.28, P < 0.01). CL rates were faster in young patients and in those with low-VWF:Ag levels. CL rates of FVIII are higher in blood Group O versus non-blood Group O persons (5.02 ± 0.38 vs. 4.00 ± 0.32 ml·kg⁻¹·h⁻¹, t = 2.53, P = 0.02).

Conclusions:

Chinese boys with severe HA have similar PK values to other ethnic groups and large differences in FVIII PK between individual patients. Age, blood group, and VWF:Ag levels are important determining factors for FVIII CL.

The role of emicizumab, a bispecific factor IXa- and factor X-directed antibody, for the prevention of bleeding episodes in patients with hemophilia A

Hemophilia A, characterized by impaired or absent expression of factor VIII, has long been managed via direct factor replacement. Functionally, factor VIII acts as a cofactor for factor IXa and allows activation of factor X, which, in combination with factor V, generates thrombin. Bispecific antibodies such as emicizumab are recombinant, monoclonal antibodies capable of recognizing and binding to two distinct antigenic targets simultaneously; emicizumab binds factors IXa and X, resulting in spatial approximation and activation of factor X, thereby mimicking the actions of factor VIII. Critically, the presence of antifactor VIII antibodies, for example, inhibitors, impacts neither the mechanism nor the efficacy by which emicizumab functions. The results and interim analyses of the emicizumab clinical trials, HAVEN 1, 2, 3, and 4, are additionally reviewed and discussed.

Focusing in on use of pharmacokinetic profiles in routine hemophilia care

BACKGROUND

Emergence of population pharmacokinetic models for prediction of individual pharmacokinetic (PK) profiles facilitates individualization of prescribed prophylactic therapy for patients with hemophilia A and B and may have a favorable impact on clinical outcomes and annual factor utilization. How providers approach the integration and application of these data into routine clinical practice is not clear.

OBJECTIVE

To explore the potential application of and barriers to incorporating PK profiles into current hemophilia prophylaxis decision making.

METHODS

A facilitated group discussion of hematologists practicing within the federally-supported United States Hemophilia Treatment Center Network was conducted. Separately, a group of parents of patients with severe hemophilia less than 18 years of age participated in a focus group on individualizing prophylactic factor regimens with the use of PK data.

RESULTS

Physician participants constructed a conceptual model for factors that determined their selection of hemophilia prophylaxis. These factors clustered in five groupings. When charged with creating a prophylaxis regimen for a specific clinical case including PK data, eight of nine providers generated a unique regimen. Parent focus group supported PK data use as they preferred data driven treatment decisions.

CONCLUSIONS

Clinician application of PK data for prophylaxis decision making is heterogeneous. Prospective evaluation of the use of PK-tailored prophylaxis in routine care and its impact on patient outcomes is needed. Parents perceived that, while obtaining blood draws could be challenging, images of factor activity decay informed their decisions about physical activity timing and provided an opportunity for partnership and shared decision making with their provider.

Data Analysis Protocol for the Development and Evaluation of Population Pharmacokinetic Models for Incorporation Into the Web-Accessible Population Pharmacokinetic Service - Hemophilia (WAPPS-Hemo)

BACKGROUND

Hemophilia is an inherited bleeding disorder caused by a deficiency in a specific clotting factor. This results in spontaneous bleeding episodes and eventual arthropathy. The mainstay of hemophilia treatment is prophylactic replacement of the missing factor, but an optimal regimen remains to be determined. Rather, individualized prophylaxis has been suggested to improve both patient safety and resource utilization. However, uptake of this approach has been hampered by the demanding sampling schedules and complex calculations required to obtain individual estimates of pharmacokinetic (PK) parameters. The use of population pharmacokinetics (PopPK) can alleviate this burden by reducing the number of plasma samples required for accurate estimation, but few tools incorporating this approach are readily available to clinicians.

OBJECTIVE

The Web-accessible Population Pharmacokinetic Service - Hemophilia (WAPPS-Hemo) project aims to bridge this gap by providing a Web-accessible service for the reliable estimation of individual PK parameters from only a few patient samples. This service is predicated on the development of validated brand-specific PopPK models.

METHODS

We describe the data analysis plan for the development and evaluation of each PopPK model to be incorporated into the WAPPS-Hemo platform. The data sources and structure of the dataset are discussed first, followed by the procedures for handling both data below limit of quantification (BLQ) and absence of such BLQ data. Next, we outline the strategies for building the appropriate structural and covariate models, including the possible need for a process algorithm when PK behavior varies between subjects or significant covariates are not provided. Prior to use in a prospective manner, the models will undergo extensive evaluation using a variety of techniques such as diagnostic plots, bootstrap analysis and cross-validation. Finally, we describe the incorporation of a validated PopPK model into the Bayesian post hoc model to produce individualized estimates of PK parameters.

RESULTS

Dense PK data has been collected for more than 20 brands of factor concentrate from both industry-sponsored and investigator-driven studies. The model development process is underway for the majority of molecules, with refinement and validation to be completed in 2017. Further, the WAPPS-Hemo co-investigator network has contributed more than 300 PK assessments for use in model development and evaluation. This constitutes the largest repository of this type of PK data globally.

CONCLUSIONS

The WAPPS-Hemo service aims to eliminate barriers to the uptake of individualized PK-tailored hemophilia treatment. By incorporating this tool into routine practice, clinicians can implement a personalized dosing strategy without performing rigorous sampling or complex calculations. This service is centred on validated models developed according to the robust approach to PopPK modeling described herein.

CLINICALTRIAL

ClinicalTrials.gov NCT02061072; https://clinicaltrials.gov/ct2/show/NCT02061072 (Archived by WebCite at http://www.webcitation.org/6mRIXJh55).

Advancing personalized care in hemophilia A: ten years' experience with an advanced category antihemophilic factor prepared using a plasma/albumin-free method

Detailed analysis of data from studies of recombinant antihemophilic factor produced using a plasma/albumin-free method (rAHF-PFM) in previously treated patients showed a substantial level of interpatient variation in pharmacokinetics (PKs), factor VIII dosing, and annualized bleed rate (ABR), suggesting that individual patient characteristics contributed to outcome. For example, plasma half-life (t_1/2), recovery, and clearance appeared to differ between patients aged <6 years and 10–65 years. Prophylaxis resulted in lower ABRs than episodic treatment in both age groups; better adherence to the prophylactic regimen resulted in a lower ABR in patients aged 10–65 years. The weekly frequency of dosing and adherence to dosing were both significantly and inversely related to the rate of bleeding (young children, P<0.0001 for both all bleeds and joint bleeds; older patients, P<0.0001 for all bleeds and P<0.05 for joint bleeds), as was adherence to dosing frequency (P<0.0001 for all comparisons). A post-marketing randomized study of prophylaxis demonstrated that a PK-guided dosing regimen, based on an individual patient’s rAHF-PFM PK (infusion interval, estimated t_1/2, and recovery), was as effective as standard prophylaxis and that both prophylactic regimens were superior to episodic treatment with respect to ABR and quality of life measures. Thus, compared with standard prophylaxis, the PK-guided regimen achieved comparable efficacy with fewer weekly infusions. A two-compartment population PK model describes the PK data across the entire age range and forms the basis for future PK-guided therapy with rAHF-PFM. The model confirmed a shorter t_1/2 and faster clearance of rAHF-PFM in children <6 years of age versus patients ≥10 years and predicted similar PK parameters with either a full or reduced blood sampling schedule, offering the potential for the use of PK-guided, individualized treatment in the routine clinical care setting.

Population pharmacokinetics of plasma-derived factor IX in adult patients with haemophilia B: implications for dosing in prophylaxis

PURPOSE

Knowledge of the pharmacokinetics (PK) of plasma-derived factor IX (FIX) is still inadequate, with conflicting findings on its elimination half-life and as yet no analysis of the variance in PK between and within individuals. The aim of the study was thus to characterize the PK of plasma-derived FIX, including estimates of variance between and within patients, in adult patients and to predict the variation between individuals in dose requirement to produce a target trough level during regular prophylaxis.

METHODS

Plasma FIX versus time data were compiled from four published and one unpublished PK study involving a total of 26 adult patients with severe haemophilia B. The number of PK assessments per patient varied between one and eight, yielding in total 893 measured FIX levels from 80 study occasions. A population PK model was developed to describe the whole dataset. Parameter values from the model were used to calculate the dose requirement to maintain a trough level of 1% of normal FIX activity in each patient.

RESULTS

The disposition of FIX was well described by a three-compartment PK model. The median elimination half-life was 31 h, and the variation between individuals was modest both in PK and in dose requirement during twice-weekly prophylaxis.

CONCLUSION

With twice weekly dosing, the need for PK-based dose tailoring of FIX in adult patients appears to be limited. However, monitoring FIX levels should be considered in children, in patients who do not respond satisfactorily to standard dosing, and if treatment is switched from plasma-derived to recombinant FIX.