Comparative pharmacokinetics of plasma- and albumin-free recombinant factor VIII in children and adults: the influence of blood sampling schedule on observed age-related differences and implications for dose tailoring

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.

Medical co-morbidities of patients with haemophilia: pain, obesity and hepatitis C

Clinical care of patients with haemophilia (PWH) has progressed rapidly over the past decade. Current therapy has allowed patients with haemophilia to live longer and many patients are now experiencing the co-morbidities of the general population. In this review article, we focus on three common diseases states that affect PWH: chronic pain, obesity and hepatitis C. Pain has been a co-morbidity for many years and PWH often have unusual needs for chronic pain relief compared to the general population. Obesity is not only increasing in the general population but also in patients with hereditary bleeding disorders. The co-morbidity of obesity not only causes increased pain progression and joint damage but also affects the dosing of factor concentrates. Finally, hepatitis C is known to have infected the majority of patients who received non-virally inactivated pooled factor concentrates in the past. New treatment regimens have been developed that allow the nearly uniform cure of chronic hepatitis C with a short course of oral medications.

Partnering to change the world for people with haemophilia: 6(th) Haemophilia Global Summit, Prague, Czech Republic, 24-26(th) September 2015

The 6(th) Haemophilia Global Summit was held in Prague, Czech Republic, in September 2015. The programme was designed by an independent Scientific Steering Committee of haemophilia experts and aimed to share optimal management strategies for haemophilia at all life stages, explore recent potential advances in the management of haemophilia A and B and discuss challenges in haemophilia care. In this supplement from the meeting, Dan Hart reviews the lessons that can be learnt from cost-constrained environments with regard to improving care for people with haemophilia globally. Sébastien Lobet discusses the importance of physical activity for optimising care and Roseline d'Oiron and Jan Blatný consider the role of real-world data in understanding the effect of treatment in a clinical setting over the long term and the true impact of treatment on the day-to-day life of the patient. Gili Kenet addresses the current challenges relating to the optimal management of prophylaxis, and Gerry Dolan and Cedric Hermans discuss the value of pharmacokinetic (PK) parameters in informing treatment decisions. Cedric Hermans and Valérie Libotte explore the importance of considering social and occupational development factors as an integral part of haemophilia care, and Jan Astermark reviews key strategies to predict and prevent inhibitor development.

The use of pharmacokinetics in dose individualization of factor VIII in the treatment of hemophilia A

INTRODUCTION

Hemophilia A is a bleeding disorder resulting from a lack of clotting factor VIII (FVIII), and treatment typically consists of prophylactic replacement of the deficient factor. However, high between subject variability precludes the development of a 'one size fits all' dosing strategy and necessitates an individualized approach. We sought to summarize the data on the pharmacokinetics of FVIII available as a basis for the development of population pharmacokinetic models to be used in dose tailoring. Areas covered: We reviewed the pharmacokinetics of FVIII as used for the treatment of hemophilia A, with a focus on the variability observed between patients and the application of pharmacokinetic methods to dose individualization. We also explored the covariates affecting pharmacokinetic parameters, the differences between plasma-derived and recombinant FVIII and the development of extended half-life products. Expert opinion: The pharmacokinetics of factor VIII in patients with hemophilia shows a high interpatient variability, and is affected by age, weight, level of von Willebrand factor, and blood group. A population approach to estimating individual pharmacokinetics is likely to provide the most successful strategy to tailor factor concentrate dosing to the individual needs and to ensure optimal patient outcomes, while also improving the cost-effectiveness of prophylactic replacement therapy.

Rationale for individualizing haemophilia care

Owing to the heterogeneity in the clinical phenotype of haemophilia A and B, it is now recognized that disease severity (based on factor VIII/IX activity) may no longer be the most appropriate guide for treatment and that a 'one-size-fits-all' approach is unlikely to achieve optimal therapy. Based on the present literature and consensus views of a group of experts in the field, this article highlights key gaps in the understanding of the diverse relationships between bleeding phenotype and factors such as joint health, genetic susceptibility, laboratory parameters, quality of life and management of pain. Early prophylaxis is a potential 'gold standard' therapy and issues surrounding inhibitor development, variations in its clinical use and long-term outcomes are discussed. Comprehensive treatment should be individualized for all patients (including those with mild or moderate haemophilia and carriers). Wherever possible all patients should be given prophylaxis. However, adult patients with a milder haemophilia phenotype may be candidates for ceasing prophylaxis and switching to on-demand treatment. Regardless, all treatment (on-demand and prophylaxis) should be tailored towards both the patient's personal needs and their clinical profile. In addition, as the associations between risk factors (psychosocial, condition-related and treatment-related) and clinical features are unique to each patient, an individualized approach is required to enable patients to alter their behaviour in response to them. The practical methodologies needed to reach this goal of individualized haemophilia care, and the health economic implications of this strategy, are ongoing topics for discussion.

An innovative outcome-based care and procurement model of hemophilia management

Hemophilia is a rare bleeding disorder associated with spontaneous and post-traumatic bleeding. Each hemophilia patient requires a personalized approach to episodic or prophylactic treatment, but self-management can be challenging for patients, and avoidable bleeding may occur. Patient-tailored care may provide more effective prevention of bleeding, which in turn, may decrease the likelihood of arthropathy and associated chronic pain, missed time from school or work, and progressive loss of mobility. A strategy is presented here aiming to reduce or eliminate bleeding altogether through a holistic approach based on individual patient characteristics. In an environment of budget constraints, this approach would link procurement to patient outcome, adding incentives for all stakeholders to strive for optimal care and, ultimately, a bleed-free world.

Comparison of platelet-derived and plasma factor VIII efficacy using a novel native whole blood thrombin generation assay

BACKGROUND

We have recently developed a successful gene therapy approach for hemophilia A in which factor VIII (FVIII) expression is targeted to platelets by the αIIb promoter. Levels of platelet-expressed FVIII (2bF8) achieved by gene therapy may vary between individuals due to differences in ex vivo transduction and gene expression efficiency. Accurate assays to evaluate 2bF8 efficacy are desirable.

OBJECTIVE

To compare the hemostatic efficacy of 2bF8 with replacement therapy over a wide therapeutic dose range.

METHODS

Efficacy of 2bF8 was assessed using a new transgenic mouse model expressing high 2bF8 levels (LV18(tg) ). Blood from LV18(tg) mice or FVIII(null) mice infused with recombinant FVIII was mixed with FVIII(null) blood at different ratios ex vivo to achieve several concentrations of 2bF8 or plasma FVIII. Samples were evaluated with a novel native whole blood thrombin generation assay that uses recalcified whole blood without the addition of tissue factor to initiate coagulation.

RESULTS

FVIII dose dependency was observed in all five thrombin generation parameters. While the total amount of thrombin generated was similar, 2bF8 significantly accelerated thrombin generation compared with plasma FVIII. Remarkably, a 10-fold lower dose of 2bF8 than plasma FVIII (0.2% vs. 2%) significantly shortened the onset and peak of thrombin generation compared with FVIII(null) blood.

CONCLUSION

Using a new transgenic mouse model, we showed that the novel native whole blood thrombin generation assay established here can be used to monitor platelet targeted FVIII gene therapy. The higher therapeutic efficacy of 2bF8 compared with factor replacement therapy seemed to be due to acceleration of thrombin generation.

Impact of being overweight on factor VIII dosing in children with haemophilia A

INTRODUCTION

Treatment of haemophilia A (HA) requires infusions of factor VIII (FVIII) concentrates. The number of FVIII units infused to obtain a specific circulating FVIII level is calculated with the formula: [body weight (BW) (kg) × desired FVIII increase (%)]/2, with the assumption that each unit of FVIII infused per kg of BW increases the circulating FVIII level by 2%.

AIM

The aim of this study was to evaluate the impact of several morphometric parameters (BW, body mass index (BMI)-for-age, height), age and type of FVIII concentrate on FVIII recovery in children with HA.

METHODS

A total of 66 children aged between 10 and 18 with severe HA selected from six pharmacokinetic (PK) clinical trials using two recombinant FVIII concentrates were included in the analysis. Regression tree (RT) was used to identify predictors of FVIII recovery.

RESULTS

The median age was 14.5 years with a median FVIII recovery of 2.09 for all children. The median FVIII recovery was not significantly different between age groups. Two groups were created by RT: children with a BMI-for-age percentile <P95 (Median FVIII recovery: 1.94) and obese children with a BMI-for-age percentile ≥P95 (Median FVIII recovery: 2.65). The FVIII recovery was significantly different between these two groups (P < 0.001).

CONCLUSION

These results are consistent with previous studies conducted in adults with HA and confirm that the long-held and current practice of applying an arbitrary and universal recovery of two to the calculations of FVIII dosage should be abolished in both children and adults.

Perioperative management of hemophilia patients receiving total hip and knee arthroplasty: a complication report of two cases

It has been recognized that perioperative hemostasis management after joint-replacement surgery for hemophilia patients is complicated and cumbersome, due to the necessity of rigorous monitoring for clotting-factor levels throughout the infusion. Between 2005 and 2014, we examined seven patients with hemophilia A (ten joints: six hips and four knees) receiving total hip or knee arthroplasty (THA or TKA) for hemophilic arthropathy. One male patient (31 years old) showed an intra-articular hematoma formation after THA (case 1). In another male patient (46 years old) receiving TKA, the postoperative trough factor VIII level became lower significantly than reference levels (80%–100% for the 5–10 postoperative days) recommended by the guidelines from the Japanese Society on Thrombosis and Hemostasis, despite sufficient coagulant based on the guidelines being administered (case 2). In the latter patient, deep infection and hematoma formation were observed postoperatively. In this article, we provide a detailed clinical report regarding these two complication cases at the early postoperative periods, and the management of bleeding control for hemophilia patients is discussed.

Managing Haemophilia for Life: 5th Haemophilia Global Summit

The 5th Haemophilia Global Summit was held in Barcelona, Spain, in September 2014. The programme was designed by an independent Scientific Steering Committee of haemophilia experts and explored issues relevant to the practical management of haemophilia, as well as key opportunities and challenges for care in the future. The topics outlined in this supplement were selected by the Scientific Steering Committee for their relevance to improving haemophilia care globally. In this supplement from the meeting, Gerry Dolan explores pharmacokinetics and dynamics in haemophilia, and Gerry Dolan and Ian Jennings jointly address the role of the laboratory in haemophilia care. The potential benefits of low-dose prophylaxis regimens for people with haemophilia in the developing world are reviewed by Jerzy Windyga, and the question of whether 'Future haemophilia research should be undertaken in the developing world' is debated by Jerzy Windyga and Cedric Hermans. Management strategies for ankle arthropathy are discussed by Sébastien Lobet and E. Carlos Rodríguez-Merchán, and the use of ultrasound for the early detection of haemophilic arthropathy is addressed by Matteo Nicola Dario Di Minno and Víctor Jiménez-Yuste. Finally, the role of patients in the future of haemophilia care is reviewed by Brian O'Mahony.

Personalized approaches to the treatment of hemophilia A and B

The recognition that individuals respond differently to the same medication is not new and dates almost to the founding of western medicine. In the last century it came to be recognized that genetic factors influence the heterogeneity of individual responses to medications with respect to both toxicity and effectiveness. Nonetheless, it has been challenging to integrate pharmacogenetic approaches in the routine practice of medicine as the identification of biomarkers is difficult due to the inherent complexity of biological systems. Here, we present potential applications of pharmacogenetics in managing hemophilia A and B. We discuss how predicting and circumventing immunogenicity, an important impediment to treating hemophilia patients, particularly lends itself to a pharmacogenetic approach. In addition, we discuss new trends toward personalizing the management of hemophilia in clinical settings.

Recombinant factor VIII Fc fusion protein for the prevention and treatment of bleeding in children with severe hemophilia A

BACKGROUND

Prophylactic factor replacement, which prevents hemarthroses and thereby reduces the musculoskeletal disease burden in children with hemophilia A, requires frequent intravenous infusions (three to four times weekly).

OBJECTIVE

Kids A-LONG was a phase 3 open-label study evaluating the safety, efficacy and pharmacokinetics of a longer-acting factor, recombinant factor VIII Fc fusion protein (rFVIIIFc), in previously treated children with severe hemophilia A (endogenous FVIII level of < 1 IU dL(-1) [< 1%]).

METHODS

The study enrolled 71 subjects. The starting rFVIIIFc regimen was twice-weekly prophylaxis (Day 1, 25 IU kg(-1) ; Day 4, 50 IU kg(-1) ); dose (≤ 80 IU kg(-1) ) and dosing interval (≥ 2 days) were adjusted as needed. A subset of subjects had sequential pharmacokinetic evaluations of FVIII and rFVIIIFc. The primary endpoint was development of inhibitors (neutralizing antibodies). Secondary endpoints included pharmacokinetics, annualized bleeding rate (ABR), and number of infusions required to control a bleed.

RESULTS

No subject developed an inhibitor to rFVIIIFc. Adverse events were typical of a pediatric hemophilic population. The rFVIIIFc half-life was prolonged relative to that of FVIII, consistent with observations in adults and adolescents. The median ABR was 1.96 overall, and 0.00 for spontaneous bleeds; 46.4% of subjects reported no bleeding episodes on study. Ninety-three per cent of bleeding episodes were controlled with one to two infusions. The median average weekly rFVIIIFc prophylactic dose was 88.11 IU kg(-1) . At study end, 62 of 69 subjects (90%) were infusing twice weekly. Among subjects who had been previously receiving FVIII prophylaxis, 74% reduced their dosing frequency with rFVIIIFc.

CONCLUSION

Twice-weekly infusions with rFVIIIFc were well tolerated and yielded low bleeding rates in children with severe hemophilia A.

Integrated analysis of safety data from 12 clinical interventional studies of plasma- and albumin-free recombinant factor VIII (rAHF-PFM) in haemophilia A

INTRODUCTION

Antihaemophilic factor (recombinant), plasma/albumin-free method (rAHF-PFM) is a human recombinant full-length factor VIII (FVIII) approved worldwide for the control and prevention of bleeding episodes, routine prophylaxis and perioperative management in adults and children with haemophilia A.

AIM

To evaluate rAHF-PFM safety [including adverse events (AEs) and inhibitor incidence] from 12 interventional studies spanning >10 years.

METHODS

The study population comprised 418 treated patients (median age = 18.7 years) with FVIII levels ≤2% of normal, including 55 previously untreated or minimally treated patients (PUPs/MTPs) from all rAHF-PFM phase I-IV studies, excluding observational safety studies.

RESULTS

Most AEs were non-serious; only 93 AEs in 45 patients (10.8%) were related to rAHF-PFM. A total of 106 serious AEs (SAEs) occurred in 69 patients (16.5%); the most common were FVIII inhibitors (4.1%), device-related infection (1.0%) and pyrexia (0.7%). The 17 SAEs considered related to treatment consisted of FVIII inhibitors in 1 previously treated patient (PTP) (≤5 Bethesda Units [BU]) and 16 PUPs/MTPs [7/55 high titre (>5 BU), 12.7%; 9/55 low titre (≤5 BU), 16.4%]. Overall, the incidence of FVIII inhibitors was 0.36% in PTPs and 29.1% in PUPs/MTPs. No deaths or cases of hypersensitivity related to rAHF-PFM occurred.

CONCLUSION

This integrated safety analysis evaluated the safety and tolerability of rAHF-PFM in children and adults with moderately severe or severe haemophilia A in all interventional studies completed to date. It was important to review consolidated evidence as some AEs are rare. There were no new safety signals in a wide variety of clinical settings.

Role of enhanced half-life factor VIII and IX in the treatment of haemophilia

Treatment of congenital haemophilia with factor VIII and IX concentrates often requires frequent infusions. This has obvious implications in establishing effective administration strategies and, in turn, adherence. To overcome these issues, three main technologies--polyethylene-glycol, Fc-neonatal IgG1 and albumin fusion products--have emerged into various stages of clinical development. Published data indicates an approximately 1·5- and fivefold increase in half-life of factor VIII and IX, respectively, compared to standard recombinant concentrates. Studies into efficacy and safety are starting to be published. Monitoring and optimal use of these new concentrates remains unknown. Weekly factor IX prophylaxis appears to be a feasible prophylactic regimen in haemophilia B patients. Weekly longer-acting FVIII is unlikely to provide adequate prophylaxis in most patients with haemophilia A but may reduce the frequency of infusions. Ongoing clinical trials and real life experience will help shape how these products can be used in practice and their cost effectiveness. The drive for convenience however should not overshadow the ultimate goal of prophylaxis, namely, preventing bleeding and arthropathy.

Considerations in individualizing prophylaxis in patients with haemophilia A

Prophylaxis is considered optimal care for children and adults with severe haemophilia A because of its proven ability to reduce joint and other bleeding episodes. However, a 'one size fits all' approach to prophylaxis is not ideal, potentially leading to over-treatment in some individuals and under-treatment in others. Moreover, a generic plan fails to take into account a patient's lifestyle and personal preferences. This article reviews the factors contributing to bleeding risk and joint damage and uses case studies to illustrate how these contributors can be weighed to individualize the prophylactic regimen, thereby increasing the likelihood of therapeutic success.

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.

Turning severe into moderate haemophilia by prophylaxis: are we reaching our goal?

BACKGROUND

Since the introduction of prophylaxis, physicians have tried to convert the clinical phenotype of severe haemophilia (SH) into that of moderate haemophilia (MH), but the outcome of patients with SH has never been compared to that of patients with MH.

MATERIAL AND METHODS

The outcome of 80 patients with SH on long-term, intermediate dose prophylaxis was compared to that of 40 patients with MH in a single-centre study. Data on treatment history, activities (assessed by the IPAQ and HAL), quality of life (assessed by the SF-36 and EQ5D), and 5-year bleeding and clotting factor consumption were collected for patients born between 1970-1995.

RESULTS

The median age of the patients was 24 years (IQR 18-30). All patients with SH received long-term prophylaxis, which was started at a median age of 4.8 years (IQR 3.2-6.2). Among the patients with MH, ten (25%) received prophylaxis, starting at a median age of 10.8 years (IQR 3.8-13.8). The annual number of bleeds, including joint bleeds, was significantly higher in patients with SH (median 2.0 joint bleeds/year, IQR =0.8-3.7) than in patients with MH (median 0.8 joint bleeds/year, IQR =0-1.2). Due to greater use of prophylaxis, the annual clotting factor consumption of SH patients (median 2,120 IU/kg; IQR 1,514-2,768), was higher than that of MH patients (median 133 IU/kg; IQR 49-468). Patients with SH showed slightly but significantly more loss of clinical function (assessed by the Haemophilia Joint Health Score): a median of 8 points (IQR 3-15) vs a median of 2 points, IQR 0-6). Quality of life, as measured by the SF-36, EQ5D and physical activity, was similar between patients with disease of different severity, as well as compared to that of the general population.

DISCUSSION

When comparing unselected cohorts, the bleeding pattern of patients with SH does not appear to be fully converted to that of the milder bleeding pattern of MH by long-term, intermediate-dose prophylaxis, although activities and quality of life were similar.

Third Åland islands conference on von Willebrand disease, 26-28 September 2012: meeting report

The first meeting of international specialists in the field of von Willebrand disease (VWD) was held in the Åland islands in 1998 where Erik von Willebrand had first observed a bleeding disorder in some members of a family from Föglö and a summary of the meeting was published in 1999. The second meeting was held in 2010 and a report of the meeting was published in 2012. Topics covered included progress in understanding of VWD over the last 50 years; multimers; classification of VWD; pharmacokinetics and laboratory assays; genetics; treating the paediatric patient; prophylaxis; geriatrics; gene therapy and treatment guidelines. This third meeting held over 3 days covered the structure and function of von Willebrand factor (VWF); type 1 VWD, the most common form of the disease; a lifespan of pharmacokinetics in VWD; detecting inhibitors in VWD patients; and special challenges in understanding and treating the female VWD patient.

Impact of being underweight or overweight on factor VIII dosing in hemophilia A patients

Since 1981, the number of factor VIII units to infuse into patients with hemophilia A in order to achieve adequate circulating factor VIII levels has been calculated using the formula: [body weight(kg)× desired factor VIII increase(%)]/2, assuming a factor VIII recovery value of 2 for all patients. This study's aim was to evaluate the impact of several morphometric parameters and various coagulation factor concentrates on factor VIII recovery.The analysis included 201 hemophilia A adults (>18 years of age) who were carefully selected from eight pharmacokinetic clinical trials using three recombinant factor VIII concentrates (Advate®, Kogenate® FS, or ReFactoAF®/Xyntha®). Regression tree analysis was used to identify factor VIII recovery predictors. The median factor VIII recovery was 2.16 for all patients. Using regression tree analysis, patients were separated into three groups on the basis of body mass index: below 20.3 kg/m(2), between 20.3 and 29.5 kg/m(2), and 29.6 kg/m(2) or more. Each group had a significantly different median factor VIII recovery (P<0.001): 1.60, 2.14, and 2.70, respectively. The type of coagulation factor concentrate had no influence on recovery in the regression tree. In conclusion, factor VIII dosing should be adapted to underweight and overweight patients, as a factor VIII recovery of 2 does not apply to these patients. Ideal body weight should be considered instead of actual body weight in the dose calculations.

Novel coagulation factor concentrates: issues relating to their clinical implementation and pharmacokinetic assessment for optimal prophylaxis in haemophilia patients

Prophylaxis is considered the optimal treatment regimen for patients with severe haemophilia, and may be especially important in the prevention of joint disease. Novel coagulation factor concentrates with prolonged half-lives promise to improve patient treatment by enabling prophylaxis with less frequent dosing. With the call to individualize therapy in haemophilia, there is growing awareness of the need to use pharmacokinetic (PK) assessments to tailor prophylaxis. However, for new factor concentrates, it is not yet known which PK values will be most informative for optimizing prophylaxis. This topic was explored at the Eighth Zurich Haemophilia Forum. On the basis of our clinical experience and a discussion of the literature, we report key issues relating to the PK assessment of new coagulation factors and include suggestions on the implementation of PK data to optimize therapy. As both inter- and intra-individual variability in factor half-life have been reported, we suggest that frequent PK assessments should be conducted. However, to diminish the burden of more frequent sampling, sparser sampling strategies and the use of population modelling should be considered. Guidelines on how to assay new factor concentrates, and which PK parameters should be measured, are needed. Concerns were raised regarding the possibility of breakthrough bleeding, and current thinking on how to prevent breakthrough bleeding may no longer be appropriate. Finally, as treatment adherence may be more important to ensure that a therapeutic level of a new coagulation factor concentrate is maintained, behavioural techniques could be implemented to help to improve treatment adherence.

Importance of pharmacokinetics in the management of hemophilia

Hemophilia A and hemophilia B are caused by congenital deficiency of factor VIII and factor IX, respectively, and may lead to recurrent, spontaneous bleeding into the muscles and joints resulting in disabling arthropathy. Effective management is available in the form of prophylactic infusions of clotting factor concentrates which have been demonstrated to prevent bleeding episodes and greatly improve the quality of life of these patients. Prophylaxis is, however, expensive. Usual dosing regimens rely on weight based calculations but dosing with an understanding of an individual's pharmacokinetic response has been demonstrated to be more effective in predicting clotting factor levels that protect against bleeding episodes. Standard pharmacokinetic studies require a prohibitive number of time sampling points but recent population or Bayesian pharmacokinetics can be used to provide an accurate estimation of an individual's pharmacokinetic response using a limited number of sampling time points. The use of population pharmacokinetics has the potential to greatly increase the use of pharmacokinetic dosing regimens and optimize the use of clotting factor concentrates in patients with hemophilia.

Use of pharmacokinetic modelling to individualize FFP dosing in factor V deficiency

Therapy with fresh frozen plasma (FFP) confers serious risks, such as contraction of blood-borne viruses, allergic reaction, volume overload and development of alloantibodies. The aim of this study was to apply principles of pharmacokinetic (PK) modelling to individual factor content of FFP to optimize individualized dosing, while minimizing potential risks of therapy. We used PK modelling to successfully target individual factor replacement in an 8-month-old patient receiving FFP for treatment of a severe congenital factor V (FV) deficiency. The model fit for the FV activity vs. time data was excellent (r = 0.98) and the model accurately predicted FV activity during the intraoperative and postoperative period. Accurate PK modelling of individual factor activity in FFP has the potential to provide better targeted therapy, enabling clinicians to more precisely dose patients requiring coagulation products, while avoiding wasteful and expensive product overtreatment, minimizing potentially life-threatening complications due to undertreatment and limiting harmful product-associated risks.

Personalized prophylaxis

Prophylaxis is the recommended treatment for people with severe haemophilia. It is unlikely that a single prophylactic regimen, for example based on weight, would be optimal for all patients and therefore each individual should have a personalized regimen, agreed between themselves and their haemophilia centre. This regimen should take into account the individual's bleeding pattern, the condition of their musculoskeletal system, level and timing of physical activity and measurement of coagulation factor in their blood. It is important to recognize that prophylactic regimens are likely to need to change with time as the circumstances of an individual change. For example, activity may change with age or with the season and an individual's factor VIII pharmacokinetics vary with age. Knowledge of a patient's pharmacokinetics is likely to help personalize prophylaxis when combined with other information. Factor VIII pharmacokinetics are simple to measure in routine clinical practice and can be adequately calculated from 2 to 3 blood samples combined with a simple to use computer program. Prophylaxis is expensive and, in countries with a limited health care budget, ways to improve its cost effectiveness need to be considered to allow increased access to this treatment. For example, increasing the frequency of prophylaxis can dramatically reduce the amount of treatment required to sustain measureable factor levels and hence reduce cost. The introduction of longer-acting coagulation factors may necessitate a change in concepts about prophylaxis because whilst these agents may sustain an apparently adequate trough level with fewer infusions, the length of time a person spends at a low level will be increased and this could increase the risk of bleeding, especially at the time of increased physical activity. There is convincing evidence that prophylaxis is the optimal therapy for severe haemophilia, optimizing treatment for each individual and increasing access to this treatment modality are important goals for the future.

Feasibility of short message service to document bleeding episodes in children with haemophilia

The increasing emphasis on home-based treatment for the management of children with haemophilia has meant that many of these children no longer regularly report to a medical facility. Consequently, it is difficult to monitor incidence of bleeding episodes. The aim of this study was to assess the feasibility of using a short message service (SMS) to monitor incidence of bleeding episodes in children with haemophilia. One hundred and four children with moderate and severe haemophilia A or B took part in a 1-year prospective study between 2008 and 2010. Children or their parents were asked to maintain a bleeds diary. They received a weekly SMS asking whether there had been a bleeding episode in the preceding week. Response rates were calculated. Children were followed for a total of 4839 person-weeks. SMS replies were received for 4201 weeks. Thus, the rate of follow-up was 86.8%. Median responses rates were 94.2% (IQR: 86.1-100%). Weekly SMS is a feasible reporting tool for documenting bleeding episodes in children with haemophilia. It is associated with high response rates and minimal expense and intrusion. The use of SMS could be extended to encourage compliance to prophylactic treatment, particularly in adolescents with haemophilia.

The hope and reality of long-acting hemophilia products

Recombinant DNA technology and protein engineering are creating hope that we can address ongoing challenges in hemophilia care such as reducing the costs of therapy, increasing the availability to the developing world, and improving the functional properties of these proteins. Technological advances to improve the half-life of recombinant clotting factors have brought long-acting clotting factors for hemophilia replacement therapy closer to reality. Preclinical and clinical trial results are reviewed as well as the potential benefits and risks of these novel therapies.

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.

Population pharmacokinetics of recombinant factor VIII: the relationships of pharmacokinetics to age and body weight

Comparison of the pharmacokinetics (PK) of a coagulation factor between groups of patients can be biased by differences in study protocols, in particular between blood sampling schedules. This could affect clinical dose tailoring, especially in children. The aim of this study was to describe the relationships of the PK of factor VIII (FVIII) with age and body weight by a population PK model. The potential to reduce blood sampling was also explored. A model was built for FVIII PK from 236 infusions of recombinant FVIII in 152 patients (1-65 years of age) with severe hemophilia A. The PK of FVIII over the entire age range was well described by a 2-compartment model and a previously reported problem, resulting from differences in blood sampling, to compare findings from children and adults was practically abolished. The decline in FVIII clearance and increase in half-life with age could be described as continuous functions. Retrospective reduction of blood sampling from 11 to 5 samples made no important difference to the estimates of PK parameters. The obtained findings can be used as a basis for PK-based dose tailoring of FVIII in clinical practice, in all age groups, with minimal blood sampling.

Overweight and obesity in hemophilia: a systematic review of the literature

CONTEXT

As life expectancy in individuals with congenital hemophilia approaches that of the general population, we hypothesize that public health risks, including overweight and obesity, also follow a similar trend.

EVIDENCE ACQUISITION

A search of the literature included terms relating to overweight, sequelae of being overweight, and hemophilia. Studies were included if they reported the frequency or clinical significance of known complications of overweight and obesity, including musculoskeletal disease, aerobic capacity, cardiovascular disease, diabetes, hyperlipidemia, decreased quality of life, and change in pharmacokinetics of infused clotting factor in hemophilia. Recommendations from medical organizations were searched for preventive and management strategies applicable to this population.

EVIDENCE SYNTHESIS

Overweight and obesity are now more prevalent in the hemophilia population than previous generations, with rates similar to and, in certain subsets even higher, than that of the general population. Increased BMI leads to limitations in joint range of motion in the general population and even more so in persons with hemophilia.

CONCLUSIONS

Overweight and obesity in hemophilia are an increasing problem. Simple steps can be taken to encourage patients to decrease caloric intake and increase physical activity. Prevention and management of overweight, obesity, and their sequelae must be addressed in clinical practice in order to maximize the overall health of the hemophilia population.

Body weight and fat mass index as strong predictors of factor VIII in vivo recovery in adults with hemophilia A

BACKGROUND

The treatment of hemophilia A requires infusions of factor VIII (FVIII) concentrates. The number of units to be given in order to obtain the target level is calculated using the formula: [body weight (BW) × desired FVIII increase]/2, which assumes that each unit infused per kg of BW increases the FVIII level by 2%.

OBJECTIVES

The present observational study evaluated the dependence of FVIII recovery on different morphometrical variables: BW, fat mass index (FMI), body mass index, and the difference between actual and ideal BW.

PATIENTS AND METHODS

FVIII recovery was measured in 46 non-actively bleeding hemophilia A patients, being treated with a recombinant FVIII concentrate. Regression trees were used to identify morphometrical predictors of recovery.

RESULTS

The median recovery was 2.08 for all patients, 2.63 for those with a BW ≥ 81.0 kg and 1.87 for others (P < 0.001). The recovery was significantly higher when FMI was ≥ 20% compared with FMI < 15% (median recovery: 2.35 vs. 1.74; P = 0.007). Using regression trees, three groups were created: BW < 80.5 kg and FMI < 22.3%, BW < 80.5 kg and FMI ≥ 22.3% and BW ≥ 80.5 kg. Median recovery in these groups was 1.80, 2.16 and 2.63, respectively (P < 0.001).

CONCLUSIONS

The dose calculation of FVIII should take into account both BW and FMI, and be adapted to underweight or overweight patients. Comparison of the average recovery after different FVIII concentrates should keep in mind morphometrical patient characteristics.