Pharmacokinetics, coagulation factor consumption and clinical efficacy in patients being switched from full-length FVIII treatment to B-domain-deleted r-FVIII and back to full-length FVIII.

Concerns have been raised regarding pharmacokinetic performance, efficacy and safety of B-domain-deleted recombinant FVIII (BDD rFVIII). The objective of this study was to perform a retrospective survey of half-life measurements, efficacy and safety in patients with severe haemophilia A, switching treatment from full-length factor VIII (FL FVIII) to BDD rFVIII and then back to FL FVIII. We hypothesized that half-life of FVIII would be equal regardless of product and that total factor consumption and bleeding frequency would be indistinguishable. We report on inhibitor development and outcome following surgery. Patients with severe haemophilia A, exposed to BDD rFVIII were identified from a database. A retrospective analysis of laboratory data and medical notes was undertaken. No significant difference was detected between the half-life measurements during the switch from FL FVIII (T/2 median 9.15 h, range 6.4-22) to BDD rFVIII (T/2 median 9.7, range 4.7-16.8) and back to FL FVIII (T/2 median 9.0, range 5.0-19.5). There was no significant difference in coagulation factor usage (BDD rFVIII median 4803 IU kg(-1) year(-1), range 659-11 304; FL FVIII median 5349, range 1691-10 146), nor bleeds. Eleven received BDD rFVIII to cover surgical procedures, with no reports of excess bleeding. Thirty-three patients received significant exposure to BDD rFVIII and one developed a low titre inhibitor. BDD rFVIII was found to be equivalent to other FVIII products in terms of pharmacokinetics, clinical efficacy and safety in this study group.

Clinical evaluation of moroctocog alfa (AF-CC), a new generation of B-domain deleted recombinant factor VIII (BDDrFVIII) for treatment of haemophilia A: demonstration of safety, efficacy, and pharmacokinetic equivalence to full-length recombinant factor VIII.

BDDrFVIII is a B-domain deleted recombinant factor VIII (rFVIII) product for haemophilia A. Manufacture uniquely includes purification chromatography by synthetic-affinity ligand rather than murine-based monoclonal antibody, as well as an albumin-free cell culture process. BDDrFVIII was studied in 204 patients, including 62 subjects <16 years old, in two studies. A double-blind, randomized, pharmacokinetic (PK) crossover study, utilizing a central laboratory assay (one-stage (OS)) for both drug potency assignment and plasma FVIII-activity measurements, demonstrated that BDDrFVIII was PK-equivalent to a full-length rFVIII. Favourable efficacy and safety were observed: during defined routine prophylaxis in a patient population significant for preexisting target joints, nearly half (45.7%) of patients had no bleeding, and a low-annualized bleed rate (ABR) was achieved (median 1.9); 92.5% of haemorrhages (n = 187) required < or =2 infusions. Three subjects (1.5%, across both studies) developed de novo inhibitors (low-titre, transient), and the primary safety endpoint, based on a prospective Bayesian analysis, demonstrated the absence of neoantigenicity for BDDrFVIII. The PK-equivalence, based on central testing to align test and reference articles, and the novel Bayesian analysis of inhibitor safety in these investigations reflect robust experimental designs with relevance to future studies. This extensive dataset demonstrates the safety and efficacy of BDDrFVIII for haemophilia A.

Performance of recalibrated ReFacto laboratory standard in the measurement of FVIII plasma concentration via the chromogenic and one-stage assays after infusion of recalibrated ReFacto (B-domain deleted recombinant factor VIII).

The use of ReFacto Laboratory Standard (RLS) in the one-stage clotting assay was proposed to reduce the underestimation of factor VIII (FVIII) plasma concentration after the infusion of 'ReFacto' (B-domain deleted recombinant FVIII) in haemophilia A patients. Both ReFacto and RLS were recently recalibrated, with the resulting materials containing approximately 20% more protein than the previous products. The aim of this study was to evaluate the performance of recalibrated RLS in the measurement of FVIII plasma concentration after the infusion of recalibrated ReFacto. In 13 severe haemophilia A patients, 25 IU kg(-1) of ReFacto were injected intravenously. Venous blood samples were collected at 0.25, 0.5, 1, 3, 6, 9, 24, 28 and 32 h after the end of the infusion. Pharmacokinetic parameters were measured for the chromogenic and one-stage assays using International Plasma Standard (IPS) and RLS for both assays and assuming a non-compartmental drug disposition. Comparisons among assays and standards were performed using anova. Pharmacokinetic estimates obtained with the chromogenic method were in agreement with those published in the literature. The one-stage method was confirmed to be more sensitive to lower plasma concentrations of FVIII. The measured maximum plasma concentration (C(max)) was slightly higher than theoretical values and independent of the assay used. C(max), area under the curve (AUC) and volume of distribution at steady state (V(ss)) presented non-significant differences among the methods and standards used. The clinical utility of RLS in the evaluation of FVIII concentration after the infusion of ReFacto seems to be reduced since recalibration of the product.

Factor VIII recovery after a single infusion of recalibrated ReFacto in 14 severe haemophilia A patients.

A recent multicentre collaborative study showed higher estimates of ReFacto potency when assayed with ReFacto Laboratory Standard(TM) (RLS) in comparison when standards consisting of full-length factor VIII (FVIII) were used. The RLS was hence recalibrated, leading to a 20% increase in the amount of ReFacto per vial without change in the labelled potency. The primary objective of this study was to determine the incremental and in vivo recovery of the recalibrated ReFacto in patients with severe haemophilia A. Fourteen male severe haemophilia A patients (FVIII < 1 IU dL(-1)) with a cumulative previous exposure days to any FVIII product >150 were administered an intravenous infusion 50 +/- 5 IU kg(-1) of ReFacto over a 5-min period. Blood samples were collected before infusion and after 15, 30 and 60 min. FVIII clotting activity (FVIII:C) was assessed in a central laboratory by the chromogenic substrate assay. After ReFacto infusion, peak FVIII:C was obtained within 15 min for 10 patients and within 30 min for the remaining four. Mean FVIII:C at peak was 117.7 +/- 17.3 IU dL(-1). Mean incremental recovery was 2.22 +/- 0.27 IU dL(-1) per IU kg(-1) while mean in vivo recovery was 105.9 +/- 14.6%. One patient reported three mild adverse events rated as 'unrelated' to the study drug. FVIII recovery after recalibrated ReFacto infusion falls within the expected range and is similar to the values reported for other FVIII concentrates.

Classification of the kinetics of factor VIII inhibitors in haemophilia A: plasma dilution studies are more discriminatory than time-course studies.

Factor VIII inhibitors have previously been classified as type I or type II using complex experiments that study the time course of inactivation of factor VIII and the effect of varying the antibody concentration. Classification may be important to better understand inhibitor behaviour in vivo. To determine the most reliable method of classifying the kinetics of factor VIII inactivation, we studied 11 patients with haemophilia A, comprising five severe, three mild and three acquired cases, and compared the classification obtained from plasma dilution studies and time-course studies. The plasma dilution studies showed two distinctly different patterns: a steep slope with complete FVIII:C inactivation at high antibody concentrations for type I inhibitors and a FVIII:C plateau with incomplete inactivation for type II inhibitors. Six type I (four severe, one mild and one acquired) and two type II (one mild and one acquired) inhibitors were classified using either plasma samples or purified and concentrated IgG, while the remaining were undetermined owing to insufficient available plasma. In contrast, the time-course studies could not discriminate between these groups. We recommend that plasma dilution studies be used for the classification of in vitro kinetics of factor VIII inhibitors.