Development of a Web-Accessible Population Pharmacokinetic Service-Hemophilia (WAPPS-Hemo): Study Protocol

Bayesian Forecasting Utilizing Bleeding Information to Support Dose Individualization of Factor VIII

Bayesian forecasting for dose individualization of prophylactic factor VIII replacement therapy using pharmacokinetic samples is challenged by large interindividual variability in the bleeding risk. A pharmacokinetic‐repeated time‐to‐event model‐based forecasting approach was developed to contrast the ability to predict the future occurrence of bleeds based on individual (i) pharmacokinetic, (ii) bleeding, and (iii) pharmacokinetic, bleeding and covariate information using observed data from the Long‐Term Efficacy Open‐Label Program in Severe Hemophilia A Disease (LEOPOLD) clinical trials (172 severe hemophilia A patients taking prophylactic treatment). The predictive performance assessed by the area under receiver operating characteristic (ROC) curves was 0.67 (95% confidence interval (CI), 0.65–0.69), 0.78 (95% CI, 0.76–0.80), and 0.79 (95% CI, 0.77–0.81) for patients ≥ 12 years when using pharmacokinetics, bleeds, and all data, respectively, suggesting that individual bleed information adds value to the optimization of prophylactic dosing regimens in severe hemophilia A. Further steps to optimize the proposed tool for factor VIII dose adaptation in the clinic are required.

Factor VIII prophylaxis effects outweigh other hemostasis contributors in predicting severe haemophilia A joint outcomes

INTRODUCTION

The Joint Outcome Study (JOS) demonstrated that previously untreated children with severe haemophilia A treated with prophylactic factor VIII (FVIII) concentrate had superior joint outcomes at age 6 years compared to those children treated episodically for bleeding. However, variation in joint outcome within each treatment arm was not well explained.

AIM

In this study, we sought to better understand variation in joint outcomes at age 6 years in participants of the JOS.

METHODS

We evaluated the influence of FVIII half-life, treatment adherence, constitutional coagulant and anticoagulant proteins, and global assays on joint outcomes (number of joint bleeds, total number of bleeds, total MRI score and joint physical exam score). Logistic regression was used to evaluate the association of variables with joint failure status on MRI, defined as presence of subchondral cyst, surface erosion or joint-space narrowing. Each parameter was also correlated with each joint outcome using Spearman correlations.

RESULTS

Prophylaxis treatment arm and FVIII trough were each found to reduce risk of joint failure on univariate logistic regression analysis. When controlling for treatment arm, FVIII trough was no longer significant, likely because of the high level of covariation between these variables. We found no consistent correlation between any laboratory assay performed and any joint outcome parameter measured.

CONCLUSION

In the JOS, the effect of prescribed prophylactic FVIII infusions on joint outcome overshadowed the contribution of treatment adherence, FVIII half-life, global assays of coagulation and constitutional coagulation proteins. (ClinicalTrials.gov number, NCT00207597).

Comparative pharmacokinetics of two extended half-life FVIII concentrates (Eloctate and Adynovate) in adolescents with hemophilia A: Is there a difference?

Essentials The PK parameters of Eloctate vs Adynovate were compared using one-stage and chromogenic assays in 25 boys (12-18 years). The FVIII levels were taken at 3, 24, 48, and 72 hours following a dose of either FVIII; levels analyzed by WAPPS PK program. The PK profiles (half-life, clearance, and time to 5%, 3%, and 1%) were not statistically different for the two EHL FVIIIs. The significant interpatient variability in PK is mainly related to VWF levels (and blood group).

BACKGROUND

A head-to-head comparison of the pharmokinetcs (PK) of extended half-life (EHL) factor VIII (FVIII) concentrates in the same subjects has not been reported. Recently, boys (ages 12-18 years) with hemophilia A in Canada were required to switch from Eloctate to Adynovate.

OBJECTIVES

Compare the PK profiles of Eloctate vs Adynovate in the same boys.

METHODS

Boys switching from Eloctate to Adynovate prophylaxis had FVIII levels sampled at 3, 24, 48, and 72 hours following a regular prophylactic infusion of Eloctate and then 1-3 months later, of Adynovate. Testing was done by one-stage assay (OSA) and chromogenic assay (CA). The PK parameters were determined with the Web Accessible Population Pharmacokinetic Service (WAPPS)-Hemo PK tool.

RESULTS

Twenty-five boys (mean age 15.3 years; range: 12.1-18.4; 9 O blood group) underwent switching. Mean (range) terminal half-lives with the OSA were 16.1 hours (10.4 to 23.4; Eloctate) and 16.7 hours (11.0 to 23.6; Adynovate) (NS). With the CA, these were 18.0 hours (12.0 to 25.5; Eloctate) and 16.0 hours (10.3 to 22.9; Adynovate) (P = 0.001). There were no significant differences between the two EHL-FVIIIs in clearance, area under the concentration vs time curve (AUC), Vss, or time for FVIII levels to drop to 5%, 3%, and 1%. At the 72-h time point, mean observed FVIII levels following a mean dose of 39.3 IU/kg of Eloctate were 4.4% (OSA) and 4.4% (CA). For Adynovate, these were 5.1% (OSA) and 5.3% (CA) following similar doses. There was considerable interpatient variation in PK, mainly explained by differences in blood group/von Willebrand factor (VWF) levels.

CONCLUSIONS

Eloctate and Adynovate have almost identical PK parameters. When switching from one to another no prophylaxis regimen change is needed.

Efficacy and safety of simoctocog alfa (Nuwiq®) in patients with severe hemophilia A: a review of clinical trial data from the GENA program

Simoctocog alfa (human-cl rhFVIII, Nuwiq®) is a 4th generation recombinant FVIII (rFVIII), without chemical modification or fusion with any other protein/fragment. Nuwiq® is produced in a human embryonic kidney cell line (HEK293F), which ensures human-specific post-translational protein processing. Nuwiq® was evaluated in seven prospective clinical studies in 201 adult and pediatric previously treated patients (PTPs) with severe hemophilia A. The NuProtect study in 110 previously untreated patients (PUPs) is ongoing. The mean half-life of Nuwiq® was 15.1–17.1 h in PTP studies with adults and adolescents, and 12.5 h in children aged 2–12 years. Clinical trials in PTPs demonstrated the efficacy and safety of Nuwiq® in the prevention and treatment of bleeds and as surgical prophylaxis. In the NuPreviq study of pharmacokinetic (PK)-guided personalized prophylaxis in 66 adult PTPs, 83% of patients had no spontaneous bleeds during 6 months of personalized prophylaxis and 57% were treated ⩽2 per week. No FVIII inhibitors were detected in PTPs after treatment with 43,267 injections and >80 million IU of Nuwiq®. Interim data for 66 PUPs with ⩾20 exposure days to Nuwiq® in NuProtect demonstrated a low cumulative high-titer inhibitor rate of 12.8% [actual incidence 12.1% (8/66)] and convincing efficacy and safety.

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.

Using pharmacokinetics for tailoring prophylaxis in people with hemophilia switching between clotting factor products: A scoping review

The objective of this scoping review is to summarize the current use of pharmacokinetics for tailoring prophylaxis in hemophilia patients switching between clotting factor products. Patients with hemophilia may require switching of clotting factor concentrates due to a variety of factors, but there have been perceived risks associated with switching, such as inhibitor development or suboptimal protection due to inadequate dosing while titrating treatment. Studies that look at patients switching from one clotting factor concentrate to another are categorized in terms of their primary and/or secondary objectives, notably biosimilarity and comparative pharmacokinetic studies and inhibitor development studies. Research on how best to switch concentrates with respect to dosing regimen are lacking, and currently a trial‐and‐error approach is used for dosing the new factor concentrate. In the future, studies looking at the predictability of pharmacokinetics (PK) of a new factor concentrate based on individual PK knowledge of the original factor concentrate may offer clinical benefit by providing a safer switching approach and protocol.

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.

Upper-Body Exercises With External Resistance Are Well Tolerated and Enhance Muscle Activity in People With Hemophilia

BACKGROUND

Conventional nonresisted therapeutic exercises for people with hemophilia involve a careful, low-intensity approach to avoid injuries. Externally resisted exercise is highly efficient for increasing muscle strength in healthy adults but its feasibility for people with hemophilia remains unknown.

OBJECTIVE

The purpose of this study was to evaluate muscle activity during upper-body rehabilitation exercises with 2 types of external resistance and without external resistance (conventional) and to examine tolerability, kinesiophobia, and possible adverse effects derived from the session.

DESIGN

This was a cross-sectional study.

METHODS

Twelve people with hemophilia A/B (11 with severe hemophilia undergoing prophylactic treatment, 1 with mild hemophilia) participated. During the experimental session, participants completed the Tampa Scale of Kinesiophobia and performed 2 exercises-elbow flexion and shoulder abduction-with 3 conditions for each exercise: elastic resistance (externally resisted), free weights (externally resisted), and conventional nonresisted. Surface electromyography signals were recorded for the biceps brachii, triceps brachii, upper trapezius, and middle deltoid muscles. After the session, exercise tolerability and kinesiophobia were assessed. Adverse effects were evaluated 24 and 48 hours after the session.

RESULTS

Externally resisted exercises provided greater muscle activity than conventional nonresisted therapeutic exercises. The exercises were generally well tolerated and there was no change in kinesiophobia following the session. No adverse effects were observed in the following days.

LIMITATIONS

Small sample size was the main limitation.

CONCLUSIONS

In people with severe hemophilia undergoing prophylactic treatment, elbow flexion and shoulder abduction exercises with external resistance at moderate intensities are feasible and provide greater muscle activity than nonresisted conventional exercises.

Optimizing bleed prevention throughout the lifespan: Womb to Tomb

The focus of care providers, patients and families is the ability to tailor care for persons with haemophilia (PWH) across the lifespan. Care requires knowledge of the bleeding disorder and age-related complications, risk of therapeutic interventions, and evaluation of individual characteristics that contribute to outcomes. The ultimate goal is to live a normal life without the burden of bleeding, for PWH and carriers. A wide range of therapeutic options is required to achieve personalized care. Over the last decade, substantial therapeutic advantages have been achieved in the treatment of haemophilia that include the development of a robust array of factor concentrates, novel haemostatic agents, and increased knowledge and awareness of disease associated outcomes and risk factors. Significant strides on the road to accessible gene therapy have been realized. This increased range of therapeutic modalities provides options for development and implementation of care plans for each patient at each stage of life that are more flexible compared to prior care regimens. Paradigms for management of haemophilia are changing. As a community, we must work together to use these resources wisely, to learn from outcomes with new therapies and diagnostic tools, to assure all patients can achieve improved care and outcomes regardless of disease state or country of origin.

Common themes and challenges in hemophilia care: a multinational perspective

OBJECTIVE

To identify ways that provision of hemophilia care can be maximized at the local level, irrespective of available resources or cultural or geographic challenges.

METHODS

The SHIELD group used its multinational experience to share examples of local initiatives that have been employed to deliver optimal hemophilia care.

RESULTS

The examples were reviewed and categorized into four key themes: guidelines and algorithms for delivery of care; collaboration with patients and allied groups for care and education; registries for the monitoring of treatment and outcomes and health care planning and delivery; and opportunities for personalization of care. These themes were then incorporated into a road map for collaborative care in hemophilia that reflected the contribution of best practice.

DISCUSSION

Differing healthcare reimbursement systems, budgetary constraints, and geographical and cultural factors make it difficult for any country to fully deliver ideal care for people with hemophilia. The SHIELD approach for collaborative care provides illustrative examples of how four key themes can be used to optimize hemophilia care in any setting.

ABBREVIATIONS

AHCDC: Association of Hemophilia Clinic Directors of Canada; AICE: Italian Association of Hemophilia Centres; ATHN: American Thrombosis and Hemostasis Network; EAHAD: European Association for Haemophilia and Allied Disorders; EHC: European Hemophilia Consortium; FIX: Coagulation Factor IX; FVIII: Coagulation Factor VIII; HAL: Haemophilia Activity List; HJHS: Haemophilia Joint Health Score; HTC: Hemophilia Treatment Centre; HTCCNC: Hemophilia Treatment Centre Collaborative Network of China; MASAC: Medical and Scientific Advisory Council; MDT: Multidisciplinary team; NHD: National Haemophilia Database; NHF: National Hemophilia Foundation; PK: Pharmacokinetics; POCUS: Point of care ultrasound; PWH: People with haemophilia; SHIELD: Supporting Hemophilia through International Education, Learning and Development; WFH: World Federation of Hemophilia.

Performing and interpreting individual pharmacokinetic profiles in patients with Hemophilia A or B: Rationale and general considerations

OBJECTIVES

In a separate document, we have provided specific guidance on performing individual pharmacokinetic (PK) studies using limited samples in persons with hemophilia with the goal to optimize prophylaxis with clotting factor concentrates. This paper, intended for clinicians, aims to describe how to interpret and apply PK properties obtained in persons with hemophilia.

METHODS

The members of the Working Party on population PK (PopPK) of the ISTH SSC Subcommittee on Factor VIII and IX and rare bleeding disorders, together with additional hemophilia and PK experts, completed a survey and ranking exercise whereby key areas of interest in the field were identified. The group had regular web conferences to refine the manuscript's scope and structure, taking into account comments from the external feedback to the earlier document.

RESULTS

Many clinical decisions in hemophilia are based on some form of explicit or implicit PK assessment. Individual patient PK profiles can be analyzed through traditional or PopPK methods, with the latter providing the advantage of fewer samples needing to be collected on any prophylaxis regimen, and without the need the for a washout period. The most useful presentation of PK results for clinical decision making are a curve of the factor activity level over time, the time to achieve a certain activity level, or related parameters like half-life or exposure (AUC). Software platforms have been developed to deliver this information to clinicians at the point of care. Key characteristics of studies measuring average PK parameters were reviewed, outlining what makes a credible head-to-head comparison among different concentrates. Large data collections of PK and treatment outcomes currently ongoing will advance care in the future.

CONCLUSIONS

Traditionally used to compare different concentrates, PK can support tailoring of hemophilia treatment by individual profiling, which is greatly simplified by adopting a PopPK/Bayesian method and limited sampling protocol.

Pharmacokinetics and the transition to extended half-life factor concentrates: communication from the SSC of the ISTH

Extended half-life proteins (EHL) are increasingly used in clinical practice, but there is no standardized approach to sampling, interpretation and implementation of pharmacokinetics (PK) data to maximize treatment benefit. The goal of EHL treatment is to attain a trough level sufficient to protect against spontaneous bleeds and reduce infusion frequency and limitations on individual activity and lifestyle. Performing classical PK assessments requires multiple blood samples, which is burdensome for patients and providers. Herein we review a population pharmacokinetic (popPK) approach to estimate individual PK parameters to transition patients from standard half-life (SHL) to EHL concentrates. We propose that a minimum of two to four post-infusion samples is sufficient to estimate individual PK profiles, with sufficient certainty to maintain factor levels above 1% and achieve bleed-free lifestyles. We also survey current PK use in patients transitioning to EHL, review key PK parameters and popPK models, and recommend an approach to using PK in patients initiating or switching to EHL.

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.

Evolving Complexity in Hemophilia Management

Rapid expansion of therapeutic options have increased the complexity of hemophilia care. Previously, on-demand therapy aimed to reduce morbidity and early mortality; however, now aggressive prophylaxis, particularly in children, encourages an active lifestyle. Accurate diagnosis, recognition of early threats to musculoskeletal health, and optimization of therapy are critical for both males and females affected by hemophilia. The diversity of emerging hemophilia therapies, from modified factor protein concentrates, to gene therapy, to nonfactor hemostatic strategies, provide an exciting opportunity to target unmet needs in the bleeding disorder community.

Pharmacokinetic drug evaluation of recombinant factor VIII for the treatment of hemophilia A

INTRODUCTION

The prevention of bleeding by prophylactic factor replacement is the recommended approach for the treatment of severe hemophilia. Prophylaxis should be individualized to provide the best clinical benefit to each patient. Therefore, a pharmacokinetic approach is crucial. Areas covered: This review aims to concisely describe the basic principles of pharmacokinetics of FVIII, the role of population pharmacokinetic, the available different recombinant FVIII concentrates and the new extended half-life FVIII molecules with possible improvement in hemophilia A treatment. Expert opinion: Pharmacokinetic is a useful tool to predict the outcome of replacement therapy, even though a large inter-individual variability exists, becauseof several factors: age, weight, von Willebrand factor level, blood group, active bleed, presence of inhibitors to FVIII, FVIII concentrate. Among the different recombinant FVIII concentrates pharmacokinetic differences are minor and clinically not significant. The extended half-life FVIII products brings only moderate advances, as half life extension is limited to 1.5-1.8-fold in comparison to that of native FVIII. Thus, infusions could be done every fourth, rarely fifth day to ensure a safe through level and a significant benefit can be offered only to patients treated every other day or three times weekly.

Using pharmacokinetics to individualize hemophilia therapy

Prevention and treatment of bleeding in hemophilia requires that plasma clotting factor activity of the replaced factor exceeds a defined target level. Most clinical decisions in hemophilia are based on implicit or explicit application of pharmacokinetic measures. The large interindividual variability in pharmacokinetics of factor concentrates suggests that relying on the average pharmacokinetic characteristics of factor concentrates would not allow optimizing the treatment of individual patients; for example, adjusting the frequency of infusions and targeting a specific clotting factor activity level on a case-by-case basis. However, individual pharmacokinetic profiles are seldom assessed as part of routine clinical care. Population pharmacokinetics provide options for precise and convenient characterization of pharmacokinetics characteristics of factor concentrates, simplified individual pharmacokinetic profiling, and individualized dosing. Population pharmacokinetics allow for the incorporation of determinants of interpatient variability and reduces the need for extensive postinfusion plasma sampling. Barriers to the implementation of population pharmacokinetics are the need for concentrate-specific pharmacokinetic models, Bayesian calculation power, and specific expertise for production, validation, and appraisal of forecasted estimates. Population pharmacokinetics provide an important theoretical and practical contribution to tailoring the treatment of hemophilia. The need remains for prospective exploration of the clinical impact of tailoring hemophilia treatment based on individual pharmacokinetics, and for the systematic validation of existing software solutions and concentrate-specific models.

Modeling of Body Weight Metrics for Effective and Cost-Efficient Conventional Factor VIII Dosing in Hemophilia A Prophylaxis

The total body weight-based dosing strategy currently used in the prophylactic treatment of hemophilia A may not be appropriate for all populations. The assumptions that guide weight-based dosing are not valid in overweight and obese populations, resulting in overdosing and ineffective resource utilization. We explored different weight metrics including lean body weight, ideal body weight, and adjusted body weight to determine an alternative dosing strategy that is both safe and resource-efficient in normal and overweight/obese adult patients. Using a validated population pharmacokinetic model, we simulated a variety of dosing regimens using different doses, weight metrics, and frequencies; we also investigated the implications of assuming various levels of endogenous factor production. Ideal body weight performed the best across all of the regimens explored, maintaining safety while moderating resource consumption for overweight and obese patients.

Tailoring treatment of haemophilia B: accounting for the distribution and clearance of standard and extended half-life FIX concentrates

The prophylactic administration of factor IX (FIX) is considered the most effective treatment for haemophilia B. The inter-individual variability and complexity of the pharmacokinetics (PK) of FIX, and the rarity of the disease have hampered identification of an optimal treatment regimens. The recent introduction of extended half-life recombinant FIX molecules (EHL-rFIX), has prompted a thorough reassessment of the clinical efficacy, PK and pharmacodynamics of plasma-derived and recombinant FIX. First, using longer sampling times and multi-compartmental PK models has led to more precise (and favourable) PK for FIX than was appreciated in the past. Second, investigating the distribution of FIX in the body beyond the vascular space (which is implied by its complex kinetics) has opened a new research field on the role for extravascular FIX. Third, measuring plasma levels of EHL-rFIX has shown that different aPTT reagents have different accuracy in measuring different FIX molecules. How will this new knowledge reflect on clinical practice? Clinical decision making in haemophilia B requires some caution and expertise. First, comparisons between different FIX molecules must be assessed taking into consideration the comparability of the populations studied and the PK models used. Second, individual PK estimates must rely on multi-compartmental models, and would benefit from adopting a population PK approach. Optimal sampling times need to be adapted to the prolonged half-life of the new EHL FIX products. Finally, costs considerations may apply, which is beyond the scope of this manuscript but might be deeply connected with the PK considerations discussed in this communication.

The History of Clotting Factor Concentrates Pharmacokinetics

Clotting factor concentrates (CFCs) underwent tremendous modifications during the last forty years. Plasma-derived concentrates made the replacement therapy feasible not only in the hospital but also at patients’ home by on-demand or prophylactic regimen. Virucidal methods, implemented soon after hepatitis and AIDS outbreak, and purification by Mabs made the plasma-derived concentrates safer and purer. CFCs were considered equivalent to the other drugs and general rules and methods of pharmacokinetics (PK) were applied to their study. After the first attempts by graphical methods and calculation of In Vivo Recovery, compartment and non-compartment methods were applied also to the study of PK of CFCs. The bioequivalence of the new concentrates produced by means of recombinant DNA biotechnology was evaluated in head-to-head PK studies. Since the beginning, the large inter-patient variability of dose/response of replacement therapy was realized. PK allowed tailoring haemophilia therapy and PK driven prophylaxis resulted more cost effective. Unfortunately, the need of several blood samples and logistic difficulties made the PK studies very demanding. Recently, population PK (PopPK) has been applied to the prediction of CFCs dosing by Bayesian methodology. By PopPK also sparse data may allow evaluating the appropriateness of replacement therapy.

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).