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

Kinetic Modeling for BT200 to Predict the Level of Plasma-Derived Coagulation Factor VIII in Humans

Lack of Factor VIII (FVIII) concentrates is one of limiting factors for Hemophilia A prophylaxis in resource-limited countries. Rondaptivon pegol (BT200) is a pegylated aptamer and has been shown to elevate the level of von Willebrand Factor (VWF) and FVIII in previous studies. A population pharmacokinetic model for BT200 was built and linked to the kinetic models of VWF and FVIII based on reasonable assumptions. The developed PK/PD model for BT200 described the observed kinetic of BT200, VWF, and FVIII in healthy volunteers and patients with mild-to-moderate hemophilia A from two clinical trials. The developed model was evaluated using an external dataset in patients with severe hemophilia A taking recombinant FVIII products. The developed and evaluated PK/PD model was able to describe and predict concentration-time profiles of BT200, VWF, and FVIII in healthy volunteers and patients with hemophilia A. Concentration-time profiles of FVIII were then predicted following coadministration of plasma-derived FVIII concentrate and BT200 under various dosing scenarios in virtual patients with severe hemophilia A. Plasma-derived products, that contain VWF, are more accessible in low-resource countries as compared to their recombinant counterparts. The predicted time above 1 and 3 IU/dL FVIII in one week was compared between scenarios in the absence and presence of BT200. A combination dose of 6 mg BT200 once weekly plus 10 IU/kg plasma-derived FVIII twice weekly maintained similar coverage to a 30 IU/kg FVIII thrice weekly dose in absence of BT200, representing only 22% of the FVIII dose per week.

Clinical benefits of a Bayesian model for plasma-derived factor VIII/VWF after one year of pharmacokinetic-guided prophylaxis in severe/moderate hemophilia A patients

INTRODUCTION

Individual pharmacokinetic (PK) profiling in hemophilia A (HA) helps to individualize prophylaxis using population PK models (popPK). A specific popPK model for plasma-derived factor VIII containing von-Willebrand Factor (pdFVIII/VWF) was developed.

AIM

To compare standard versus PK-driven prophylaxis, using a generic or a specific popPK model for pdFVIII/VWF.

MATERIALS AND METHODS

A prospective study conducted in HA patients in prophylaxis with pdFVIII/VWF (Fanhdi®) comparing three one-year study periods: (1) standard prophylaxis, (2) PK-guided prophylaxis using a generic pdFVIII popPK model which described FVIII activity irrespective of FVIII concentrate, and (3) PK-guided prophylaxis with specific pdFVIII/VWF popPK model. PK parameters analyzed were half-life, trough levels (TL) at 24, 48 and 72 h, and time to reach FVIII levels of 1, 2, 5% (T5%). Clinical outcomes were dose/kg, FVIII consumption, annualized bleeding rate (ABR), annualized joint bleeding rate (AJBR), spontaneous and traumatic bleeds.

RESULTS

Of the 30 analyzed patients, 28 had severe HA and the median age was 31.2. Fifteen patient's prophylaxis doses were PK-adjusted. After the generic PK-guided prophylaxis period, younger patients showed more joint bleeds, a shorter half-life, and lower TL48, TL72 and T5%. Using the specific pdFVIII/VWF popPK model compared with standard prophylaxis, a lower spontaneous AJBR was observed in the entire cohort and in patients aged >15 years. Additionally, lower spontaneous ABR was reported in patients aged ≤15 years comparing specific and generic models.

CONCLUSIONS

PK-guided prophylaxis with a specific pdFVIII/VWF popPK model allowed treatment individualization and improved bleeding control in routine clinical practice, especially in younger patients with short pdFVIII/VWF half-lives.

Status Toward the Implementation of Precision Dosing in Children

Precision dosing is progressing beyond the conceptual and proof-of-concept stages toward implementation. As the availability of dosing algorithms, tools, and platforms increases, so do the investment in technology services and actual implementation of clinical services offering these solutions to patients. Nowhere is this needed more than in pediatric populations, which are still reliant on adult drug development and bridging strategies to support dosing, often in the absence of actual dose-finding studies in the target pediatric population. Still, there is more work to be done to ensure that proper governance of these services is maintained, and that sustainability of these early implementations is guided by new science as it evolves and meaningful outcome data to confirm that such services deliver on both clinical and economic return on investment. In addition, the field should ensure that all approaches beyond a therapeutic drug monitoring-driven, pharmacokinetic-centric approach should be considered as the tools and services evolve, especially when pediatric-specific pharmacokinetic/pharmacodyamic and pharmacogenetic data are available and shown to be useful to guide dosing. This review evaluates current pediatric precision dosing efforts, highlighting their utility, longevity, and sustainability and assesses the current process for implementing such approaches examining current barriers that stand in the way of broader implementation and the stakeholders that must engage to ensure its ultimate success.

Pediatric Dose Selection for Therapeutic Proteins

In selecting optimal dosing regimens in support of the clinical use of monoclonal antibodies and other therapeutic proteins in pediatric indications, the unique pharmacokinetic properties of this class of biologics, as well as the underlying physiologic and pathophysiologic processes and their modulation by childhood growth and development, needs to be appreciated. During drug development, first-in-pediatric dose selection is a capstone event in the pediatric investigation plan that relies heavily on extrapolation of pharmacokinetic and pharmacodynamic data from adult to pediatric populations. It is facilitated by combinations of pharmacometric approaches, including allometry, physiologically based pharmacokinetic modeling, and population pharmacokinetic analyses, although data on reliability and qualification of some of these tools in the context of therapeutic proteins are still limited but emerging. Presented data suggest nonlinear relationships between body weight and both clearance and volume of distribution for therapeutic proteins in pediatric populations, with allometric exponents of 0.75 and 0.8, respectively. For newborns and infants (<1 year), even higher nonlinearity seems to occur. Translation of the quantitative characterization of the pediatric pharmacokinetics of therapeutic proteins into dosing regimens for the drug label requires compromising between precision dosing and clinical practicability, with tiered dosing algorithms based on size or age strata being the currently most frequently applied methodology.

Population Pharmacokinetics of Clotting Factor Concentrates and Desmopressin in Hemophilia

Hemophilia A and B are bleeding disorders caused by a deficiency of clotting factor VIII and IX, respectively. Patients with severe hemophilia (< 0.01 IU mL⁻¹) and some patients with moderate hemophilia (0.01–0.05 IU mL⁻¹) administer clotting factor concentrates prophylactically. Desmopressin (d-amino d-arginine vasopressin) can be applied in patients with non-severe hemophilia A. The aim of administration of factor concentrates or desmopressin is the prevention or cessation of bleeding. Despite weight-based dosing, it has been demonstrated that factor concentrates still exhibit considerable pharmacokinetic variability. Population pharmacokinetic analyses, in which this variability is quantified and explained, are increasingly performed in hemophilia research. These analyses can assist in the identification of important patient characteristics and can be applied to perform patient-tailored dosing. This review aims to present and discuss the population pharmacokinetic analyses that have been conducted to develop population pharmacokinetic models describing factor levels after administration of factor VIII or factor IX concentrates or d-amino d-arginine vasopressin. In total, 33 publications were retrieved from the literature. Two approaches were applied to perform population pharmacokinetic analyses, the standard two-stage approach and non-linear mixed-effect modeling. Using the standard two-stage approach, four population pharmacokinetic models were established describing factor VIII levels. In the remaining 29 analyses, the non-linear mixed-effect modeling approach was applied. NONMEM was the preferred software to establish population pharmacokinetic models. In total, 18 population pharmacokinetic analyses were conducted on the basis of data from a single product. From all available population pharmacokinetic analyses, 27 studies also included data from pediatric patients. In the majority of the population pharmacokinetic models, the population pharmacokinetic parameters were allometrically scaled using actual body weight. In this review, the available methods used for constructing the models, key features of these models, patient population characteristics, and established covariate relationships are described in detail.

Development and evaluation of the population pharmacokinetic models for FVIII and FIX concentrates of the WAPPS-Hemo project

BACKGROUND

The Web-Accessible Population Pharmacokinetic Service (WAPPS) project generates individually predicted pharmacokinetic (PK) profiles and tailored prophylactic treatment regimens for haemophilic patients, which rely on a set of population PK (PopPK) models providing concentrate-specific priors for the Bayesian forecasting methodology.

AIM

To describe the predictive performance of the WAPPS PopPK models in use on the WAPPS-Hemo platform.

METHODS

Data for modelling include dense PK data obtained from industry sponsored and independent PK studies, and dense and sparse data accumulated through WAPPS-Hemo. WAPPS PopPK models were developed via non-linear mixed-effect modelling taking into account the effects of covariates and between-individual-and sometimes between-occasion-variability. Model evaluation consisted of (a) prediction-corrected Visual Predictive Check (pcVPC), (b) Limited Sampling Analysis (LSA) and (c) repeated hold-out cross-validation.

RESULTS

Thirty-three WAPPS PopPK models built on data from 3188 patients (ages 1-78 years) under treatment by factor VIII or IX products (FVIII, FIX) were evaluated. Overall, models exhibit excellent performance characteristics. The pcVPC shows that the observed PK data fall within acceptable 90% interpercentile predictive bands. A slight overprediction beyond the expected half-life, an anticipated result of using sparse data, occurs for some models. The LSA results in lower than 3% of relative error for FVIII and FIX products and 16% for engineered FIX products. Cross-Validation analysis yields relative errors lower than 1.5% and 1.4% in estimates of half-life and time to 0.02 IU/mL, respectively.

CONCLUSION

The WAPPS-Hemo models consistently showed excellent performance characteristics for the intended use for Bayesian forecasting of individual PK profiles.