Break-through bleeding in relation to predicted factor VIII levels in patients receiving prophylactic treatment for severe hemophilia A

Analysis of low frequency bleeding data: the association of joint bleeds according to baseline FVIII activity levels

Many studies in the field of haemophilia and other coagulation deficiencies require analyses of bleeding frequencies. In haemophilia, the association of bleeding frequency with factor VIII (FVIII) activity levels is known from experience, but significant results are lacking. Bleeding frequencies in haemophilia are highly skewed count data, with large proportions of zeros. Both the skewness and the high amount of zeros pose a problem for standard (linear) modelling techniques. This study investigated the optimal analysing strategy for bleeding data by using the association of residual clotting factor level and number of joint bleeds in moderate and mild patients treated on demand as example. In total, 433 patients with moderate (27%) and mild (73%) haemophilia A treated on demand were included in this study. One year of self-reported data on joint bleed frequency and baseline clotting factor activity were analysed using Poisson, negative binomial, zero-inflated Poisson, and zero-inflated negative binomial distributions. Multivariate regression analysis using negative binomial distribution provided the optimum data analytical strategy. This model showed 18% reduction [Rate ratio (RR) 0.82; 95%confidence interval (CI) 0.77-0.86] of bleeding frequency with every IU dL(-1) increase in residual FVIII activity. The actual association is expected to be higher because of exclusion (30 out of 463 patients) of patients on prophylaxis (baseline FVIII levels 0.01-0.06 IU mL(-1)). The best way to analyse low frequency bleeding data is using a negative binomial distribution.

Enabling normal psychophysical development in children with hemophilia: the choice for prophylaxis

Hemophilia A and B, the congenital deficiencies of coagulation factors VIII and IX, are characterized by recurrent joint and muscle bleeding episodes and progressive musculoskeletal damage (hemophilic arthropathy). Primary prophylaxis – that is, the regular infusion of factor concentrates after the first hemarthrosis and/or before 2 years of age – is now recognized as the first-choice treatment for children with severe hemophilia. Preventing bleeding from an early age enables avoidance of the clinical impact of hemophilic arthropathy and the consequences regarding psychosocial development and quality of life for these children. Interestingly, recent data suggest a role for early prophylaxis in also preventing inhibitor development, the most serious complication of treatment in hemophilia. Secondary prophylaxis, initiated after 2 years of age or after two or more joint bleeds, aims to avoid (or delay) the progression of arthropathy. In addition, better outcomes and better quality of life have been reported with earlier treatment. This review summarizes the evidence, current clinical strategies and open issues regarding prophylxis in children with hemophilia.

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

BACKGROUND

Dose tailoring of coagulation factors requires reliably estimated and reproducible pharmacokinetics (PK) in the individual patient.

OBJECTIVES

To investigate the contribution of both biological and methodological factors to the observed variability of factor VIII (FVIII) PK, with the focus on differences between children and adults, and to examine the implications for dosing.

PATIENTS

Data from 52 1-6-year-old and 100 10-65-year-old patients with hemophilia A (FVIII < or = 2 IU dL(-1)) in three clinical studies were included.

RESULTS

In vivo recovery was lower, weight-adjusted clearance was higher and FVIII half-life was on average shorter in children than in adults. However, a reduced blood sampling schedule for children was estimated to account for up to one half of the total observed differences. Intrapatient variance in PK was smaller than interpatient variance in 10-65-year-olds. Age and ratio of actual to ideal weight only showed weak relationships with PK parameters. Variance in PK caused large variance in the calculated dose required to maintain a target FVIII trough level during prophylactic treatment.

CONCLUSION

Differences in blood sampling schedules should be taken into account when results from different PK studies are compared. However, even with this consideration, PK cannot be predicted from observable patient characteristics but must be determined for the individual. Because the influence of reducing the blood sampling was minor in comparison to the true variance between patients, a reduced blood sampling protocol can be used. Low intrapatient variability supports the use of PK measurements for dose tailoring of FVIII.

A United Kingdom Haemophilia Centre Doctors' Organization guideline approved by the British Committee for Standards in Haematology: guideline on the use of prophylactic factor VIII concentrate in children and adults with severe haemophilia A

Consensus-based guidelines supported by the literature are presented on the role of prophylactic administration of factor VIII concentrate in children and adults with severe haemophilia A. The timing of initiation of prophylaxis, the choice of prophylactic regimen, monitoring, management of breakthrough bleeding and education of the patient and family are discussed.

Review of antihemophilic factor injection for the routine prophylaxis of bleeding episodes and risk of joint damage in severe hemophilia A

Individuals with severe factor VIII deficiency experience recurrent hemorrhages and develop progressive joint damage. Large retrospective, nonrandomized studies of patient cohorts followed over decades show that factor prophylaxis initiated at an early age before the onset of recurrent bleeding reduces the incidence of hemophilic arthropathy. Two recent prospective, multicenter, randomized trials conducted in Europe (the ESPRIT study) and the USA (the Joint Outcome Study) confirm the efficacy of prophylaxis in the prevention of hemarthroses and arthropathy. Regular prophylaxis initiated in early childhood enhances the quality of life for patients with severe hemophilia and reduces the risk of inhibitor development. The substantial costs of such preventative therapy may be offset by the reduced expenditures that the care of degenerative joint disease in adult hemophilia patients would otherwise require.

Limited blood sampling for pharmacokinetic dose tailoring of FVIII in the prophylactic treatment of haemophilia A

The aim of this study was to evaluate the use of limited blood sampling and Bayesian analysis to estimate the pharmacokinetics (PK) and tailor the dose of factor VIII (FVIII) in an individual patient. In a Bayesian analysis, PK parameters are estimated from only a few plasma concentration measurements, using a previously established PK model. First the necessary model was created using intense blood sampling FVIII data from 10 patients. Then FVIII data from another 21 patients were used for 'clinical' evaluation. Three scenarios were created retrospectively by reduction of the original 7-sample data set; blood sampling at 4, 24 and 48 h, at 8 and 30 h and at 24 h after the infusion. PK parameters were estimated for each individual using Bayesian analysis and compared with those obtained using conventional methods from the full data. The accuracy of predictions of FVIII levels during prophylactic treatment 5-17 months later and implications for dose tailoring were also investigated. Blood sampling at 4, 24 and 48 h was found to give practically the same PK information as a full, conventional (7-10-sample) study. Even a single 24-h FVIII level provided adequate data for initial dose tailoring and gave predictions of FVIII levels 5-17 months later that were not appreciably worse than predictions based on the full PK analysis. By contrast, dose tailoring based on body weight failed completely. In conclusion, PK-based dose tailoring of FVIII can be performed using limited blood sampling during prophylactic treatment.

Factor VIII requirement to maintain a target plasma level in the prophylactic treatment of severe hemophilia A: influences of variance in pharmacokinetics and treatment regimens

BACKGROUND

Prophylactic factor (F)VIII has been shown to reduce bleeds and arthropathy in patients with severe hemophilia A.

OBJECTIVES

Assuming that the trough FVIII level is an important determinant of the efficacy of prophylaxis, this paper addresses the effect of the inter-patient variability in pharmacokinetics and different dosing regimens on trough levels.

METHODS

Simulations used FVIII half-lives and in vivo recoveries (IVR), observed during clinical trials with Advate [Antihemophilic Factor (Recombinant), Plasma/Albumin-Free Method], and commonly used prophylactic regimens to calculate their effect on FVIII levels during prophylaxis.

RESULTS AND CONCLUSIONS

Half-life and dose frequency had a larger effect on trough FVIII and time per week with FVIII<1 IU dL(-1) than IVR and infused dose per kg. The combined effect of these parameters resulted in substantial inter-patient variability in the amount of FVIII required to sustain a desired trough level. Prophylactic regimens based on Monday, Wednesday, Friday dosing were less cost effective in maintaining a desired trough level throughout the week. Dose escalation on Friday to cover the weekend would require potentially harmful doses of FVIII in many patients, especially in young children where more than 50% would require a Friday dose of over 100 IU kg(-1) and some would require more than 400 IU kg(-1). Knowledge of individual patients' half-lives and alteration of frequency of infusions may allow the more cost-effective use of FVIII and potentially expand access to prophylaxis to a greater number of patients, especially in regions where healthcare resources are scarce.

Efficacy and safety of secondary prophylactic vs. on-demand sucrose-formulated recombinant factor VIII treatment in adults with severe hemophilia A: results from a 13-month crossover study

BACKGROUND

Hemarthroses in severe hemophilia precipitate physical, psychosocial and financial difficulties.

OBJECTIVE

To compare the effects of secondary prophylaxis with on-demand sucrose-formulated recombinant factor VIII (rFVIII-FS) therapy in severe hemophilia A.

PATIENTS AND METHODS

This open-label study included patients aged 30-45 years with factor VIII (FVIII) coagulant activity < 1 IU dL(-1) who were using on-demand FVIII treatment. Patients were treated with rFVIII-FS on demand for 6 months, followed by 7 months prophylaxis (20-40 IU kg(-1), three times per week, with the first month considered a run-in). The primary endpoint was the number of hemarthroses.

RESULTS

Twenty patients were enrolled (n = 19 completed); the mean age was 36.4 years, and 16 had target joints. The median (25-75%) number of joint bleeds decreased significantly with prophylaxis [0 (0-3)] vs. on-demand [15 (11-26); P < 0.001] therapy. The number of all bleeds was 0 (0-3) vs. 20.5 (14-37; P < 0.001), respectively. Median (range) total Gilbert scores improved after prophylaxis [18 (3-39)] compared with on-demand [25 (4-46)] therapy, predominantly reflecting the improved bleeding score. Median time from last prophylactic infusion to bleed was 2 days; 82.5% of bleeds occurred 2-3 days after the last infusion. Median 48-h and 72-h FVIII trough levels measured during months 10 and 13 were consistently > 6 and > 4 IU dL(-1), respectively. Treatment was well tolerated, and no inhibitor formation was observed.

CONCLUSION

Secondary prophylaxis with rFVIII-FS significantly reduced the frequency of hemarthroses compared with on-demand therapy in adult patients with severe hemophilia A.

Comparison of kaolin and tissue factor activated thromboelastography in haemophilia

A limitation of bypassing agent therapy for haemophilia patients with inhibitors is the absence of a laboratory assay, which predicts the clinical response to treatment. Recent investigations have demonstrated the potential for thromboelastography to assess the effects of bypassing agent therapy in this patient population. While tissue factor activation has been used in several prior studies, a recent multicentre study failed to demonstrate an expected concentration-response effect of rFVIIa and called into question the tissue factor activation methods that have been employed. A comparison of kaolin to two concentrations of tissue factor as the activation method for thromboelastography was investigated in patients with haemophilia. We performed kaolin and tissue factor activated thromboelastography on blood from inhibitor and non-inhibitor patients with and without addition of rFVIIa and rFVIII. The results demonstrate that kaolin leads to a longer R, K and angle than the higher dilution of tissue factor (1:17 000) at baseline (no factor) and after addition of rFVIIa for both the inhibitor and non-inhibitor patients. Kaolin led to a longer R and K in comparison to a low dilution of tissue factor (1:42 000) following the addition of rFVIIa in the inhibitor patients. The longer R and K allows for better discrimination of the effects of rFVIIa thus making kaolin the most sensitive activation method in this setting. Thus kaolin activated thromboelastography should be considered an effective, perhaps the most effective, activator when utilizing thromboelastography to assess the effects of rFVIIa in haemophilia patients with inhibitors.

Models for prediction of factor VIII half-life in severe haemophiliacs: distinct approaches for blood group O and non-O patients

Background

Von Willebrand factor (VWF) is critical for the in vivo survival of factor VIII (FVIII). Since FVIII half-life correlates with VWF-antigen pre-infusion levels, we hypothesized that VWF levels are useful to predict FVIII half-life.

Methodology

Standardized half-life studies and analysis of pre-infusion VWF and VWF-propeptide levels were performed in a cohort of 38 patients with severe haemophilia A (FVIII <1 IU/ml), aged 15–44 years. Nineteen patients had blood-group O. Using multivariate linear regression-analysis (MVLR-analysis), the association of VWF-antigen, VWF-propeptide, age and body-weight with FVIII half-life was evaluated.

Principal Findings

FVIII half-life was shorter in blood-group O-patients compared to non-O-patients (11.5±2.6 h versus 14.3±3.0 h; p = 0.004). VWF-antigen levels correlated with FVIII half-life considerably better in patients with blood-group non-O than O (Pearson-rank = 0.70 and 0.47, respectively). Separate prediction models evolved from MVLR-analysis for blood-group O and non-O patients, based on VWF-antigen and VWF/propeptide ratio. Predicted half-lives deviated less than 3 h of observed half-life in 34/38 patients (89%) or less than 20% in 31/38 patients (82%).

Conclusion

Our approach may identify patients with shorter FVIII half-lives, and adapt treatment protocols when half-life studies are unavailable. In addition, our data indicate that survival of FVIII is determined by survival of endogenous VWF rather than VWF levels per se.

Recombinant factor VIII in the management of hemophilia A: current use and future promise

Hemophilia A is a rare inherited bleeding disorder due to mutation of the gene that encodes the coagulation protein factor VIII. Historically, prior to the availability of treatment with factor VIII preparations, most boys died from uncontrolled bleeding, either spontaneous bleeding or after injury, before reaching 20 years of age. One of the most impressive triumphs of modern medicine is that with current recombinant factor VIII replacement therapy, a boy born in the 21st century with severe hemophilia A can anticipate a normal life expectancy with essentially no permanent complications from bleeding. For severe hemophilia A, current optimal treatment should have two goals: first, to provide sufficient factor VIII to prevent spontaneous bleeding, and second, to provide sufficient factor VIII to have normal coagulation function after any trauma. However, the replacement therapy requires tremendous resources for effective use, and remains extraordinarily expensive. Thus there are opportunities for further advances in therapy for hemophilia A. Two major concerns continue to trouble current optimal treatment approaches: some patients will develop neutralizing antibodies during the first 50 infusions of therapeutic factor VIII, and second, to administer therapeutic factor VIII every other day in young boys often requires placement of a central venous access device, and such use carries the life-threatening risks of infection and thrombosis. Because of the effectiveness of current therapy, any new developments in treatment will require significant concerns for safety, both immediate and in the long term. A number of research groups seek to prolong the biological efficacy of infused recombinant factor VIII. Currently, one such promising development is in the advanced stages of clinical trial. The goals will be to improve further the quality of life of an individual with severe hemophilia A, and to reduce the burden of current treatment strategies on families and medical resources. Hopefully, the hemophilia community will continue to participate actively in the clinical trials needed to address these new challenges.