A cross-over pharmacokinetic and thrombogenicity study of a prothrombin complex concentrate and a purified factor IX concentrate

Using pharmacokinetics for tailoring prophylaxis in people with hemophilia switching between clotting factor products: A scoping review

The objective of this scoping review is to summarize the current use of pharmacokinetics for tailoring prophylaxis in hemophilia patients switching between clotting factor products. Patients with hemophilia may require switching of clotting factor concentrates due to a variety of factors, but there have been perceived risks associated with switching, such as inhibitor development or suboptimal protection due to inadequate dosing while titrating treatment. Studies that look at patients switching from one clotting factor concentrate to another are categorized in terms of their primary and/or secondary objectives, notably biosimilarity and comparative pharmacokinetic studies and inhibitor development studies. Research on how best to switch concentrates with respect to dosing regimen are lacking, and currently a trial-and-error approach is used for dosing the new factor concentrate. In the future, studies looking at the predictability of pharmacokinetics (PK) of a new factor concentrate based on individual PK knowledge of the original factor concentrate may offer clinical benefit by providing a safer switching approach and protocol.

Performing and interpreting individual pharmacokinetic profiles in patients with Hemophilia A or B: Rationale and general considerations

OBJECTIVES

In a separate document, we have provided specific guidance on performing individual pharmacokinetic (PK) studies using limited samples in persons with hemophilia with the goal to optimize prophylaxis with clotting factor concentrates. This paper, intended for clinicians, aims to describe how to interpret and apply PK properties obtained in persons with hemophilia.

METHODS

The members of the Working Party on population PK (PopPK) of the ISTH SSC Subcommittee on Factor VIII and IX and rare bleeding disorders, together with additional hemophilia and PK experts, completed a survey and ranking exercise whereby key areas of interest in the field were identified. The group had regular web conferences to refine the manuscript's scope and structure, taking into account comments from the external feedback to the earlier document.

RESULTS

Many clinical decisions in hemophilia are based on some form of explicit or implicit PK assessment. Individual patient PK profiles can be analyzed through traditional or PopPK methods, with the latter providing the advantage of fewer samples needing to be collected on any prophylaxis regimen, and without the need the for a washout period. The most useful presentation of PK results for clinical decision making are a curve of the factor activity level over time, the time to achieve a certain activity level, or related parameters like half-life or exposure (AUC). Software platforms have been developed to deliver this information to clinicians at the point of care. Key characteristics of studies measuring average PK parameters were reviewed, outlining what makes a credible head-to-head comparison among different concentrates. Large data collections of PK and treatment outcomes currently ongoing will advance care in the future.

CONCLUSIONS

Traditionally used to compare different concentrates, PK can support tailoring of hemophilia treatment by individual profiling, which is greatly simplified by adopting a PopPK/Bayesian method and limited sampling protocol.

Tailoring treatment of haemophilia B: accounting for the distribution and clearance of standard and extended half-life FIX concentrates

The prophylactic administration of factor IX (FIX) is considered the most effective treatment for haemophilia B. The inter-individual variability and complexity of the pharmacokinetics (PK) of FIX, and the rarity of the disease have hampered identification of an optimal treatment regimens. The recent introduction of extended half-life recombinant FIX molecules (EHL-rFIX), has prompted a thorough reassessment of the clinical efficacy, PK and pharmacodynamics of plasma-derived and recombinant FIX. First, using longer sampling times and multi-compartmental PK models has led to more precise (and favourable) PK for FIX than was appreciated in the past. Second, investigating the distribution of FIX in the body beyond the vascular space (which is implied by its complex kinetics) has opened a new research field on the role for extravascular FIX. Third, measuring plasma levels of EHL-rFIX has shown that different aPTT reagents have different accuracy in measuring different FIX molecules. How will this new knowledge reflect on clinical practice? Clinical decision making in haemophilia B requires some caution and expertise. First, comparisons between different FIX molecules must be assessed taking into consideration the comparability of the populations studied and the PK models used. Second, individual PK estimates must rely on multi-compartmental models, and would benefit from adopting a population PK approach. Optimal sampling times need to be adapted to the prolonged half-life of the new EHL FIX products. Finally, costs considerations may apply, which is beyond the scope of this manuscript but might be deeply connected with the PK considerations discussed in this communication.

Clinical experience with a highly purified factor IX concentrate in patients undergoing surgical operations

The haemostatic efficacy of a new highly purified factor IX concentrate, prepared by metal chelate affinity chromatography, was assessed in 13 patients with haemophilia B undergoing a variety of surgical operations. Four of the patients had developed post-operative thromboembolic complications following previous operations, when treated with a prothrombin complex concentrate. None of the patients in the present series developed any evidence of post-operative thrombotic complications. Effective haemostasis was achieved in all patients, with the exception of a surgical bleed in one case, and late post-operative bleeding in a second patient when the factor IX activity fell below 20iu/dl. The product is treated with a solvent-detergent process that destroys lipid-enveloped viruses, while the affinity chromatography process during manufacture removes in excess of 4 log10 of a non-lipid-enveloped virus. In follow-up studies, none of the patients has shown evidence of fresh infection from the concentrate, when assessed by virological markers. It is concluded that this high-purity concentrate (tradenane 'Replenine') is effective for the treatment of patients with haemophilia B who undergo surgical operations.

Secondary prophylaxis with factor IX concentrates: continuous infusion

Haemophilia patients may require prolonged treatment during peri-operative period or life-threatening bleedings. Intermittent bolus infusions of factor concentrates have been used successfully for many years. However, pharmacokinetics may vary among products and patients, and the wide fluctuations in factor levels during therapy can make management inaccurate and unsafe. Specific protocols for continuous infusion have been developed, which may decrease factor utilization, facilitate laboratory monitoring of factor levels, and may decrease the overall cost of therapy. Continuous infusion of different clotting factor concentrates (factor VIII, factor IX, porcine factor VIII, rFVIIa, and activated prothrombin complex concentrates) has been associated with excellent haemostasis and safety: indeed, by continuous infusion unsafe low troughs or dangerous high concentrations can be avoided. In this review, the pharmacokinetic aspects of the continuous infusion of plasma-derived and recombinant factor IX concentrates are showed. Finally, the advantages and disadvantages of continuous infusion are discussed.

Haemophilia B: Christmas disease

Haemophilia B is an inherited bleeding disorder associated with a deficiency of coagulation factor IX. The hallmark of the severe phenotype is recurrent and spontaneous bleeding into joints, which can lead to joint deformity and arthritis at an early age. Recombinant factor IX is now increasingly regarded as the treatment of choice because it does not transmit human pathogens. All patients in the UK now receive this product exclusively. Conventional treatment now consists of the administration of recombinant factor IX concentrate on a prophylactic basis to prevent bleeds and, hence, minimise disability in the long term. Trials of gene therapy are also underway, but these are in the very early stages and will not be a realistic option for at least another 20 years.

Blood Products for Hemophilia

Hemophilia is an inherited bleeding disorder, which in its severe form is characterized by recurrent hemarthrosis and internal bleeding. In the absence of effective treatment the prognosis is poor, but the development of blood products in the last few decades has transformed the outlook, and patients can now live essentially normal lives. Treatment options vary around the world, with cryoprecipitate still the mainstay of therapy in many developing countries. Many patients were infected with hepatitis and/or HIV through the use of coagulation factor concentrates before the introduction of physical methods of viral inactivation in the mid-1980s. In more affluent countries, the debate in recent years has focused on the relative merits of plasma versus recombinant products. Coagulation factor concentrates are expensive, and cost-benefit and quality-of-life studies will assume an increasing importance in guiding the selection of products. Looking to the future, genetic engineering offers the potential to create coagulation factors with enhanced properties, such as reduced immunogenicity and prolonged half-life. Transgenic animals are a potential source of therapeutic materials. Several trials of gene therapy for hemophilia are already underway.

A retrospective survey on the safety of Replenine®, a high-purity factor IX concentrate

PURPOSE

To assess the safety of a plasma-derived highly purified factor IX concentrate (Replenine) in routine clinical use.

METHODS

Following guidelines entitled Safety Assessment of Marketed Medicines (SAMM), safety data were collected in the UK by retrospective review of the hospital notes of 114 patients who received an estimated 14.8 million IU of Replenine. Included were 40 patients undergoing 44 surgical procedures or dental extractions [corrected].

RESULTS

The study detected a total of nine adverse events (AEs), four of which were possibly product-related, four that were unrelated to the product and one whose causality was unknown. None of these cases had been notified to the manufacturer through conventional spontaneous reporting procedures. One patient was switched from Replenine because of infusion site irritation, but no unexpected adverse reactions were noted. There were no reports of virus transmission or new factor IX inhibitor development. The mean factor IX recovery value was 1.44 IU/dl per IU/kg (95%CI: 1.31-1.57 IU/dl per IU/kg).

CONCLUSIONS

The study was a practical application of the SAMM guidelines to the collection of pharmacovigilance data on patients with Haemophilia B. Replenine is well tolerated in routine clinical practice.

Guidelines on the selection and use of therapeutic products to treat haemophilia and other hereditary bleeding disorders

Evidence based guidelines are presented on the selection and use of therapeutic products to treat haemophilia. These guidelines offer advice based on the best published scientific and medical information. They will be reviewed regularly by UKHCDO Advisory Committee. Included are details of therapeutic products available in the UK to treat patients with haemophilia and other bleeding disorders and the background information on which the recommendations are based are presented.

MonoFIX-VF, a new mono-component factor IX concentrate: a single-centre continuous-infusion study

MonoFIX-VF, a monocomponent factor IX concentrate, has replaced the use of Prothrombinex-HT as the treatment of choice for patients with factor IX deficiency in Australia. The haemostatic effect of MonoFIX-VF, administered by continuous infusion, was assessed in four subjects being treated for 10 bleeding episodes including five surgical procedures. MonoFIX-VF was found to be a safe and effective treatment for patients with haemophilia B.

Concentrate safety and efficacy

Safety from transmission of infections through plasma-derived clotting factor concentrates is assured by improved donor screening, serological testing of individual donations and direct viral testing of small plasma pools. Modern viral-inactivation techniques are highly effective. Recombinant concentrates stabilized in human albumin are being superaeded by those with other stabilizers. Recently reported discrepancies between estimates of concentrate potency from in vitro assays versus in vivo recovery, depending upon type of assay and reference standard used, are not fully resolved.