The effect of unmeasurable endogenous plasma factor activity levels on factor VIII dosing in patients with severe hemophilia A

Estimated prophylactic dose required to achieve 3% trough as a function of age and concentrate class in multi-country severe WAPPS-Hemo haemophilia patients

INTRODUCTION

Web-Accessible Population-Pharmacokinetic Service-Haemophilia (WAPPS-Hemo) data are available to study factor-concentrate usage, defined as the required weekly dose to achieve a 3% trough (WD3T), across standard and extended half-life (SHL/EHL) products.

AIM

To provide baseline usage data including (i) differences across plasma-derived (pdSHL) versus recombinant (rSHL) products, (ii) SHL versus EHL, and (iii) effect of age and positive inhibitor history.

METHODS

PK profiles (n = 14,416 patients, 0.3-85.2 years) and linear mixed effects models were used to estimate usage versus age, controlling for significant factors, using 95% confidence intervals to perform comparisons across all ages and posthoc tests to assess the differences.

RESULTS

Average usage was significantly higher for pdSHL versus rSHL in patients with a positive inhibitor history (PIH; 1.9-2.5 times higher), for SHL versus EHL (4-10 times), and was significantly associated with age.

CONCLUSION

Baseline usage patterns from 2017 to early 2023 provide a benchmark for assessing the impact of emerging technologies in haemophilia.

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.

Comparison of single subject and population-based pharmacokinetics for optimizing prophylaxis with simoctocog alfa in patients with haemophilia A

INTRODUCTION

The use of pharmacokinetic assessment for optimal prophylactic dosing of factor concentrates in haemophilia has gained increasing enthusiasm over the last decade. However, blood sampling on several occasions is burdensome and limited sampling using population-based PK is appealing.

AIM

To compare the pharmacokinetics and dosing recommendations for prophylaxis using six-point single subject versus population-based method (WAPPS-Hemo) for simoctocog alfa (Nuwiq^® ).

METHODS

Twelve adult patients with severe haemophilia A received a factor VIII (FVIII) dose of ≈50 IU/kg, and the activity was measured pre-infusion and at 30 min, 6, 9, 24 and 48 h post-infusion. Half-life (t¹ /₂ ), weight-normalized AUC and time to troughs of 5%, 3% and 1% were calculated. The correlation between the PK algorithms was assessed using intraclass correlations (ICC) and dosing estimations were provided.

RESULTS

WAPPS-Hemo yielded a slightly longer mean t¹ /₂ , but the overall correlation between the methods was good (ICC ≥0.79) The time to troughs of 5%, 3% and 1% showed ICCs ≥0.86. For all variables, the most converging limited time point was 6+48 h. Additional time points did not improve the correlation. Despite similar pharmacokinetics, the mean estimated dose for a specific trough level varied from 60% less to 20% more using the population-based approach. The time to 1% and the corresponding dose was sensitive to the baseline assumption.

CONCLUSION

Our data support the use of population-based PK for patients on simoctocog alfa prophylaxis but also indicates differences, stressing the importance of the sampling scheme and monitoring actual FVIII levels achieved.

A novel, point-of-care, whole-blood assay utilizing dielectric spectroscopy is sensitive to coagulation factor replacement therapy in haemophilia A patients

BACKGROUND

Reliable monitoring of coagulation factor replacement therapy in patients with severe haemophilia, especially those with inhibitors, is an unmet clinical need. While useful, global assays, eg thromboelastography (TEG), rotational thromboelastometry (ROTEM) and thrombin generation assay (TGA), are cumbersome to use and not widely available.

OBJECTIVE

To assess the utility of a novel, point-of-care, dielectric microsensor - ClotChip - to monitor coagulation factor replacement therapy in patients with haemophilia A, with and without inhibitors.

METHODS

The ClotChip T_peak parameter was assessed using whole-blood samples from children with severe haemophilia A, with (n = 6) and without (n = 12) inhibitors, collected pre- and postcoagulation factor replacement therapy. ROTEM, TGA and chromogenic FVIII assays were also performed. Healthy children (n = 50) served as controls.

RESULTS

ClotChip T_peak values exhibited a significant decrease for samples collected postcoagulation factor replacement therapy as compared to baseline (pretherapy) samples in patients with and without inhibitors. A difference in T_peak values was also noted at baseline among severe haemophilia A patients with inhibitors as compared to those without inhibitors. ClotChip T_peak parameter exhibited a very strong correlation with clotting time (CT) of ROTEM, endogenous thrombin potential (ETP) and peak thrombin of TGA, and FVIII clotting activity.

CONCLUSIONS

ClotChip is sensitive to coagulation factor replacement therapy in patients with severe haemophilia A, with and without inhibitors. ClotChip T_peak values correlate very well with ROTEM, TGA and FVIII assays, opening up possibilities for its use in personalized coagulation factor replacement therapy in haemophilia.