Kinetic evaluation of four Factor VIII concentrates by model-independent methods

Dosing for Personalized Prophylaxis in Hemophilia A Highly Varies on the Underlying Population Pharmacokinetic Models

BACKGROUND

Model-informed personalized prophylaxis with factor VIII (FVIII) replacement therapy aimed at higher trough levels is becoming indispensable for patients with severe hemophilia A. This study aimed to identify the most suitable population pharmacokinetic (PK) models for personalized prophylaxis using various FVIII products and 2 clinical assays and to implement the most suitable one in open-access software.

METHODS

Twelve published population PK models were systematically compared to predict the time above target (TaT) for a reference dosing occasion. External validation was performed using a 5-point PK data from 39 adult patients with hemophilia A with FVIII measured by chromogenic substrate (CSA) and 1-stage assays (OSAs) using NONMEM under 3 different conditions: a priori (with all FVIII samples blinded), a posteriori (with 1 trough sample), and general model fit (with all FVIII samples including the reference dosing occasion provided).

RESULTS

On average, the baseline covariate models overpredicted TaT (a priori; bias -3.8 hours to 49.6 hours). When additionally including 1 previous trough FVIII sample before the reference dosing occasion (a posteriori), only 50% of the models improved in bias (-1.0 hours to 36.5 hours) and imprecision (22.4 hours and 60.7 hours). Using all the time points (general model fit), the models accurately predicted (individual TaT less than ±12 hours compared with the reference) 62%-90% and 33%-74% of the patients using CSA and OSA data, respectively. Across all scenarios, predictions using CSA data were more accurate than those using the OSA data.

CONCLUSIONS

One model performed best across the population (bias: -3.8 hours a priori, -1.0 hours a posteriori , and 0.6 hours general model fit ) and acceptably predicted 44% (a priori) to 90% ( general model fit ) of the patients. To allow the community-based evaluation of patient-individual FVIII dosing, this model was implemented in the open-access model-informed precision dosing software "TDMx."

A Practical, One-Clinic Visit Protocol for Pharmacokinetic Profile Generation with the ADVATE myPKFiT Dosing Tool in Severe Hemophilia A Subjects

Standard pharmacokinetic (PK) assessments are demanding for persons with hemophilia A, requiring a 72-hour washout and 5 to 11 timed blood samples. A no-washout, single-clinic visit, sparse sampling population PK (PPK) protocol is an attractive alternative. Here, we compared PK parameters obtained with a traditional washout, 6-sampling time point PPK protocol with a no-washout, single-clinic visit, reverse 2-sampling time point PPK protocol in persons with severe hemophilia A (SHA) receiving ADVATE. A total of 39 inhibitor-negative males with SHA (factor VIII activity [FVIII:C] < 2%) were enrolled in a prospective sequential design PK study. Participants completed a washout, 6-sampling time point PPK protocol as well as a no-washout, reverse 2-sampling time point protocol, with samples taken during a single 3-hour clinic visit 24 hours post home infusion of FVIII and then 3 hours post infusion in clinic. FVIII:C levels were analyzed by one-stage and chromogenic assays; blood group and von Willebrand factor antigen (VWF:Ag) were determined; and PK parameters were analyzed using the ADVATE myPKFiT dosing tool. There was moderate to almost perfect agreement for the PK parameters obtained with the 2- and the 6- point PPK protocols using a one-stage FVIII:C assay and a substantial to almost perfect agreement using a chromogenic FVIII:C assay. Significant associations between specific PK parameters and blood group and VWF:Ag were observed. The no-washout, single-clinic visit, reverse 2-sampling time point PPK protocol can be used in the routine clinical setting since it demonstrates sufficient accuracy compared with the more demanding and less practical washout, 6-sampling time point PPK protocol in persons with SHA receiving ADVATE.

Analysis of Survival Curves: Statistical Methods Accounting for the Presence of Long-Term Survivors

Some anti-cancer treatments (e. g., immunotherapies) determine, on the long term, a durable survival in a small percentage of treated patients; in graphical terms, long-term survivors typically give rise to a plateau in the right tail of the survival curve. In analysing these datasets, medians are unable to recognize the presence of this plateau. To account for long-term survivors, both value-frameworks of ASCO and ESMO have incorporated post-hoc corrections that upgrade the framework scores when a survival plateau is present. However, the empiric nature of these post-hoc corrections is self-evident. To capture the presence of a survival plateau by quantitative methods, two approaches have thus far been proposed: the milestone method and the area-under-the-curve (AUC) method. The first approach identifies a long-term time-point in the follow-up (“milestone”) at which survival percentages are extracted. The second approach, which is based on the measurement of AUC of survival curves, essentially is the rearrangement of previous methods determining mean lifetime survival; similarly to the milestone method, the application of AUC can be “restricted” to a pre-specified time-point of the follow-up. This Mini-Review examines the literature published on this topic. The main characteristics of these two methods are highlighted along with their advantages and disadvantages. The conclusion is that both the milestone method and the AUC method are able to capture the presence of a survival plateau.

Setting the stage for individualized therapy in hemophilia: What role can pharmacokinetics play?

Replacement therapy with clotting factor concentrates (CFC) is the mainstay of treatment in hemophilia. Its widespread application has led to a dramatic decrease in morbidity and mortality in patients, with concomitant improvement of quality of life. However, dosing is challenging and costs are high. This review discusses benefits and limitations of pharmacokinetic (PK)-guided dosing of replacement therapy as an alternative for current dosing regimens. Dosing of CFC is now primarily based on body weight and based on its in vivo recovery (IVR). Benefits of PK-guided dosing include individualization of treatment with better targeting, more flexible blood sampling, increased insight into association of coagulation factor levels and bleeding, and potential overall lowering of overall costs. Limitations include a slight burden for the patient, and availability of closely collaborating, experienced clinical pharmacologists.

Break-through bleeding in relation to pharmacokinetics of Factor VIII in paediatric patients with severe haemophilia A

INTRODUCTION

As the pharmacokinetics (PK) of factor VIII (FVIII) is individualized in children with haemophilia A (HA), PK parameters may be indicators of patients' bleeding phenotype and instruction for their personalized replacement program.

AIM

The aim of this study was to investigate the possible relationship between PK/FVIII level and bleeding frequency in Chinese paediatric patients with severe (HA).

METHODS

A total of 24 patients were enrolled in Beijing Children's Hospital from February to October 2015, all of whom were given 50 IU/kg of FVIII concentrates after a 72-hours washout period. Samples' activities (FVIII:C) were tested at 5 time points, using WinNonlin software for PK testing, and then the individual half-life(t_1/2 ) and the time (h) of FVIII concentrations <1 IU/dL within a week during prophylaxis were calculated. Baseline and the annual bleeding rate (ABR), annual joint bleeding rate (AJBR) were recorded and analyzed.

RESULTS

The mean t_1/2 of FVIII was 10.20 ± 2.72 hours and the mean time of FVIII <1 IU/dL in 1 week was 44.7 hours (-38.56 to 102.33 hours). A significant relationship between t_1/2 of FVIII and ABR₀ /AJBR₀ (baseline bleeding) was found (R²  = 0.75 and 0.62, P < .001). Besides, baseline and the annual bleeding rate during prophylactic treatment of haemophilia had a positive correlation with the time (hours) of FVIII <1 IU/dL in 1 week (R²  = 0.67 and 0.52, P < .001).

CONCLUSION

t_1/2 was an important indicator to prevent bleeding in severe HA; the frequency of bleeding will be reduced with the increased of t_1/2 of FVIII. The data also demonstrates that increasing the time with a FVIII<1 IU/dL is associated with an increased rate of bleeding during prophylaxis.

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.

Allometry of factor VIII and informed scaling of next-generation therapeutic proteins

Allometric scaling has been applied to the pharmacokinetics (PK) of factor VIII (FVIII), but published relationships are based on relatively small subsets of available data. Numerous next-generation forms of FVIII are being developed (e.g., Fc fusion, PEGylated, and liposomal formulations) and traditional PK scaling of these products would not incorporate the wealth of existing knowledge for current FVIII therapy in humans. We conducted a meta-analysis and developed allometric relationships of FVIII from over 100 PK studies collected from literature. Normalized Wajima curves were used to relate mean FVIII profiles between species. An "informed scaling" approach was derived for predicting first-in-human PK parameters and demonstrated with a case study for an Fc fusion FVIII. NCA values for FVIII PK were well described by the allometric equations CL = 6.59 W(0.85) and V(ss) = 65.0 W(0.97). A subset of studies characterized by two-compartment modeling showed strong linearity in scaling of total clearance (CL) and central volume, but more variability in distributional CL and peripheral volume. Wajima curves for FVIII superimposed across species and the disposition of Fc fusion FVIII in humans was well predicted by "informed scaling." This approach might be generally applicable for predicting human PK of next-generational therapeutics.

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.

Pediatric Dosing and Body Size in Biotherapeutics

Although pediatric doses for biotherapeutics are often based on patients' body weight (mg/kg) or body surface area (mg/m²), linear body size dose adjustment is highly empirical. Growth and maturity are also important factors that affect the absorption, distribution, metabolism and excretion (ADME) of biologics in pediatrics. The complexity of the factors involved in pediatric pharmacokinetics lends to the reconsideration of body size based dose adjustment. A proper dosing adjustment for pediatrics should also provide less intersubject variability in the pharmacokinetics and/or pharmacodynamics of the product compared with no dose adjustment. Biological proteins and peptides generally share the same pharmacokinetic principle with small molecules, but the underlying mechanism can be very different. Here, pediatric and adult pharmacokinetic parameters are compared and summarized for selected biotherapeutics. The effect of body size on the pediatric pharmacokinetics for these biological products is discussed in the current review.

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.

Integrated analysis of safety and efficacy of a plasma- and albumin-free recombinant factor VIII (rAHF-PFM) from six clinical studies in patients with hemophilia A

BACKGROUND

Hemophilia A is an X-linked bleeding disorder that results from insufficient levels of factor VIII (FVIII) coagulant activity.

OBJECTIVE

To evaluate the efficacy and safety of ADVATE rAHF-PFM (Baxter Healthcare Corporation), a recombinant FVIII concentrate manufactured without human or bovine blood-derived additives, and to assess the effect of compliance with prophylactic use in preventing bleeding episodes (BEs).

METHODS

Clinical data were integrated from six prospective studies. Two hundred thirty-four hemophilia A subjects (FVIII levels < or = 2%) (median age 14.7 (range: 0.02 - 72.7) years) were included.

RESULTS

BEs were managed with one or two infusions and nearly all (1953/1956) responded to treatment. Compliance with a prophylactic treatment regimen significantly reduced the incidence of BEs (p = 0.0061) and prevented non-traumatic joint BEs (median annualized BE rate was 0). One previously treated subject developed an inhibitor; no other safety concerns were observed.

CONCLUSIONS

These results reinforce the efficacy and safety of rAHF-PFM and suggest that compliance is an essential contributor to the effectiveness of prophylaxis in the treatment of hemophilia A.

Plasma and albumin-free recombinant factor VIII: pharmacokinetics, efficacy and safety in previously treated pediatric patients

BACKGROUND

The pharmacokinetics of factor VIII replacement therapy in preschool previously treated patients (PTPs) with hemophilia A have not been well characterized.

OBJECTIVES

To assess the pharmacokinetics, efficacy and safety of a plasma-free recombinant FVIII concentrate, ADVATE [Antihemophilic Factor (Recombinant), Plasma/Albumin-Free Method, rAHF-PFM], in children < 6 years of age with severe hemophilia.

PATIENTS/METHODS

Fifty-two boys, one girl, mean (+/- SD) age 3.1 +/- 1.5 years and >or= 50 days of prior FVIII exposure, were enrolled in a prospective study of ADVATE rAHF-PFM at 23 centers.

RESULTS

The mean terminal phase half-life (t(1/2)) was 9.88 +/- 1.89 h, and the mean adjusted in vivo recovery (IVR) was 1.90 +/- 0.43 IU dL(-1) (IU kg(-1))(-1). Over the 1-6-year age range, t(1/2) of rAHF-PFM increased by 0.40 h year(-1). IVR increased by 0.095IU dL(-1)(IU kg(-1))(-1) (kg m(-2))(-1) in relation to body mass index (BMI). Patients primarily received prophylaxis. Median (range) annual joint bleeds were 0.0 (0.0-5.8), 0.0 (0.0-6.1) and 14.2 (0.0-34.5) for standard prophylaxis, modified prophylaxis and on-demand treatment, respectively. Bleeds were managed in 90% (319/354) of episodes with one or two rAHF-PFM infusions; response was rated excellent/good in 93.8% of episodes. Over a median 156 exposure days, no FVIII inhibitors were detected and no related severe adverse events or unusual non-serious adverse events were seen.

CONCLUSIONS

Children < 6 years of age appear to have shorter FVIII t(1/2) and lower IVR values than older subjects. However, these parameters increased with age (t(1/2)) and BMI (adjusted IVR), respectively. rAHF-PFM was clinically effective and well tolerated, with no signs of increased immunogenicity in previously treated young children with hemophilia A.

A Limited Sampling Strategy for Estimating Individual Pharmacokinetic Parameters of Coagulation Factor VIII in Patients With Hemophilia A

Therapeutic drug monitoring of factor VIII is well established in the treatment of patients with hemophilia attributable to important interindividual variability. The individual initial factor VIII dosage is usually calculated according to individual pharmacokinetic parameters obtained after a dose test administered before the surgery, using at least five-concentration data. The authors proposed a limited sampling strategy to estimate individual pharmacokinetic parameters from one- or two-concentration data in patients with hemophilia A before surgery. The mean population pharmacokinetic parameters and the interindividual variability (CV) were obtained from a group of 33 patients according to a two-compartment model using NONMEM. Eighteen additional patients were used to estimate the predictive performances of the population parameters and to evaluate the limited sampling strategies. Population parameters were clearance 2.6 mL/h per kilogram (CV 45.4%), initial volume of distribution 2.8 L (CV 21.1%). From two sampling times (0.5 and 6 hours or 0.5 and 8 hours after the end of infusion), the estimation of pharmacokinetic parameters was precise and not biased. Until now, in the hemophilic center of Lyon, the factor VIII dosage before surgery was based on the determination of the clearance, estimated from five- to nine-concentration data and on the target concentration (infusion rate = clearance x target). Ruffo et al proposed a limited sampling strategy (two-stage method) to estimate pharmacokinetic parameters from two concentration measurements drawn 3 and 9 hours after the dose. No information was given on the bias and precision of the estimation. This paper reports a one-stage method for a population pharmacokinetic study of factor VIII. The Bayesian estimation of individual pharmacokinetic parameters based on only two sampling times (0.5 and 6 hours or 0.5 and 8 hours after the end of infusion) is useful to define the best factor VIII dosage in hemophilic patients before surgery.

The pharmacokinetics of coagulation factors

In this article, we provide a summary of the generally accepted approaches to the design and analysis of studies examining the pharmacokinetic (PK) profile of an infused coagulation factor in patients with a deficiency of one or more of these factors. Furthermore, we briefly review the known PK results for various commercially available coagulation factor preparations under single and continuous infusion.

The pharmacokinetics of clotting factor therapy

Clotting factor preparations are expensive and not readily available in all parts of the world. We are still facing shortages due to limited production. Thus, it is obvious that clotting factor therapy should be optimised as far as possible. The judicious use of pharmacokinetic principles should be one of the fundaments of dosing. There are several pitfalls in studies of clotting factor pharmacokinetics, such as discrepancies between assays, inadequate blood sampling protocols, problems to define the administered dose, uncertainty in the estimation of plasma volume for in vivo recovery calculation, and post-infusion activation of the clotting factor. Thus, while the pharmacokinetics of factor VIII is well characterised there are some discrepancies in the literature on factor IX. Recombinant factor VIIa is useful to treat haemorrhages in haemophilia complicated by inhibitors. The pharmacokinetics of VIIa has been investigated, however, the relationship between plasma level of VIIa and effect needs further exploration. Important applications of clotting factor pharmacokinetics include optimising the treatment and improving its cost-effectiveness during long-term prophylaxis as well as during bleeding episodes and surgery.

Prophylactic dosing of factor VIII and factor IX from a clinical pharmacokinetic perspective

The high cost and limited availability of factor concentrates make dosing of factor VIII (FVIII) or factor IX (FIX) a crucial issue in the prophylactic treatment of haemophilia. It has often been recommended that this treatment should aim to maintain a minimum plasma level of 1% of normal coagulation factor activity (FVIII:C or FIX:C). The dosage needed is commonly given as 25-40 U kg(-1) three times weekly for FVIII or twice weekly for FIX. However, these guidelines are valid only with several qualifications. First, the actual trough levels required may vary considerably between patients. The clinical severity of haemophilia may depend on more factors than the endogenous level of FVIII:C or FIX:C. Secondly, interindividual variations in dose requirements are also due to variance in the pharmacokinetics of the coagulation factors. Pharmacokinetic calculations are useful to design optimal dosing schedules to achieve required trough levels of FVIII:C or FIX:C. Moreover, tailoring of the dosing of FVIII or FIX according to their disposition in the individual patient can markedly improve the cost-effectiveness of prophylactic treatment. However, the usefulness of in vivo recovery as a guide for prophylactic dosing seems questionable. It should be clearly understood that maintaining a certain trough level of FVIII:C or FIX:C is not an end in itself. Clinical outcome, not the achieved trough level, determines whether a dosage is adequate. Chiefly for economic reasons, the minimum effective dosage of coagulation factor should be determined and used in every patient. The dose requirement should also be re-evaluated at appropriate times.

Pharmacokinetics of factor VIII and factor IX

A survey of principal pharmacokinetic (PK) studies on factor VIII (FVIII) and factor IX (FIX) plasma- and rDNA-derived concentrates, analysed by means of the PKRD program, has been performed. Notwithstanding the accurate definition of the study design, released in 1991 by the Scientific and Standardization Committee of the International Society on Thrombosis and Haemostasis (SSC-ISTH), a large variability of PK parameters has been pointed out. In the majority of the PK studies, the size of the population is small. In this situation, a careful individualization of haemophilia therapy is strongly recommended. The tailored prediction of loading and maintenance dosages and the need for strict control of trough FVIII/IX levels are mandatory not only to decrease the risk of bleeds but also to spare financial resources. Recently, the old problem of FVIII assay standardization has again become a concern among physicians, especially after the introduction of B-domain deleted rFVIII concentrate. The discrepancies between the widely used one-stage clotting assay and the chromogenic substrate assay seem to be solved by the introduction of a product-specific laboratory standard.

Pharmacokinetic study of FFP photochemically treated with amotosalen (S-59) and UV light compared to FFP in healthy volunteers anticoagulated with warfarin

BACKGROUND

To date, no clinical trials have characterized FFP infusion efficacy, and infusion still carries infectious risk. This single-blinded crossover study compared postinfusion kinetics of FVII in photochemically treated FFP to standard FFP.

STUDY DESIGN AND METHODS

Subjects donated plasma by apheresis. Half of the collected plasma was treated with the psoralen amotosalen hydrochloride (S-59) and UVA light, and half were prepared as standard plasma. Subjects received warfarin over 4 days to lower FVII levels. On Day 4, subjects received 1 L of either treated or standard FFP. After 2 weeks, subjects underwent a regimen identical to that with the other type of FFP.

RESULTS

After warfarin ingestion, the mean FVII concentration was 0.33 IU per mL. Both types of FFP exhibited comparable FVII kinetics, with a mean peak increment of 0.10 to 0.12 IU per mL occurring at the end of infusion. The effect disappeared after 8 hours.

DISCUSSION

Study data of warfarin-treated healthy volunteers demonstrate that psoralen plus UV-treated FFP provides an equivalent in vivo coagulation response to control plasma. A 1-L dose of FFP in adults may provide an initial increment of 0.10 IU per mL of FVII. In the absence of bleeding, FVII levels return to baseline after 8 hours.

Efficacy and safety of a factor VIII-von Willebrand factor concentrate 8Y: stability, bacteriological safety, pharmacokinetic analysis and clinical experience

The present study was undertaken to evaluate stability, pharmacokinetic profile and efficacy of continuous infusion of 8Y in patients with different types of von Willebrand disease (vWD). Following reconstitution, 8Y levels of von Willebrand factor ristocetin cofactor (vWF:Rco), vWF antigen and factor VIII coagulant activity (FVIII:C) decreased to about 80% of the baseline levels; addition of low molecular weight heparin decreased the level of FVIII:C even further. Reconstituted 8Y was found to be sterile for up to 6 days postreconstitution. Ten vWD patients (four with type 2A, three with type 3, two with type 1 and one with 2N) underwent pharmacokinetic analysis. The recovery of vWF: RCo was significantly lower in patients with type 3 vWD (1.4 +/- 0.05% U(-1) kg(-1)) compared with that of the patients with types 1 (2.3 +/- 0.52% U(-1) kg(-1)) or 2A (2.0 +/- 0.06% U(-1) kg(-1)) vWD (P = 0.015). Type 3 vWD patients exhibited significantly higher vWF:RCo clearance (5.1 +/- 1.1 mL kg(-1) h(-1)) compared with that of patients with type 2A (2.8 +/- 0.7 mL kg(-1) h(-1)) and type 1 (2.6 +/- 1.0 mL kg(-1) h(-1)) vWD (P = 0.028). Accordingly, terminal half-life was lower in patients with type 3 vWD (8.0 +/- 0.6 h(-1)) compared with type 2A (12.7 +/- 5.9 h(-1)) or type 1 (14 +/- 1.2 h(-1)) vWD patients. Multimeric pattern of vWF from patients' plasma was similar to that of 8Y. In two patients treated with 8Y by continuous infusion for prevention or treatment of bleeding haemostasis was achieved. Thus, 8Y is suitable and haemostatically effective for continuous infusion treatment in patients with vWD.

Continuous factor VIII infusion therapy in patients with haemophilia A undergoing surgical procedures with plasma-derived or recombinant factor VIII concentrates

We describe the experience of a single medical centre with continuous factor VIII (FVIII) infusion therapy in a cohort of patients undergoing elective surgery. Twenty-eight patients had a total of 45 procedures. Intraoperative haemostasis was considered excellent in all 45 cases. FVIII levels were maintained between 46% and 191% of normal (median, 103%) for 2-7 days. Bleeding occurred after five procedures (11%) at times when factor VIII levels were within haemostatic range. No patient required reoperation to control bleeding. There were no cases of sepsis related to continuous infusion of factor VIII. We conclude that continuous infusion: (1) is a safe and effective means of replacement therapy in patients with haemophilia undergoing surgery; (2) provides easier monitoring and more constant coagulation factor levels; and (3) has the potential to decrease the cost of replacement therapy by reducing overall usage of product.

Pharmacokinetics of coagulation factors: clinical relevance for patients with haemophilia

Haemophilia is a recessively inherited coagulation disorder, in which an X-chromosome mutation causes a deficiency of either coagulation factor VIII (FVIII) in haemophilia A, or factor IX (FIX) in haemophilia B. Intravenous administration of FVIII or FIX can be used to control a bleeding episode, to provide haemostasis during surgery or for long term prophylaxis of bleeding. In special cases, activated factor VII (FVIIa) may be used instead of FVIII or FIX. The aim of this work is to review the pharmacokinetics of FVIII, FIX and FVIIa and to give an outline of the use of pharmacokinetics to optimise the treatment of patients with haemophilia. The pharmacokinetics of FVIII are well characterised. The systemic clearance (CL) of FVIII is largely determined by the plasma level of von Willebrand factor (vWF), which protects FVIII from degradation. Typical average CL in patients with normal vWF levels is 3 ml/h/kg, with an apparent volume of distribution at steady state (Vss) that slightly exceeds the plasma volume of the patient, and the average elimination half-life (t1/2) is around 14 hours. There are still some discrepancies in the literature on the pharmacokinetics of FIX. The average CL of plasma-derived FIX seems to be 4 ml/h/kg, the Vss is 3 to 4 times the plasma volume and the elimination t1/2 often exceeds 30 hours. FVIIa has a much higher CL (average of 33 ml/h/kg), and a short terminal t1/2 (at 2 to 3 hours). The Vss is 2 to 3 times the plasma volume. Since the therapeutic levels of coagulation factors are well defined in most clinical situations, applied pharmacokinetics is an excellent tool to optimise therapy. Individual tailoring of administration in prophylaxis has been shown to considerably increase the cost effectiveness of the treatment. Dosage regimens for the treatment of bleeding episodes or for haemostasis during surgery are also designed using pharmacokinetic data, and the advantages of using a constant infusion instead of repeated bolus doses have been explored. The influence of antibodies (inhibitors) on the pharmacokinetics of FVIII and FIX is in part understood, and the doses of coagulation factor needed to treat a patient can tentatively be calculated from the antibody titre. In conclusion, therapeutic monitoring of coagulation factor levels and the use of clinical pharmacokinetics to aid therapy are well established in the treatment of patients with haemophilia.

Comparative pharmacokinetic studies in haemophilia

The general rules of pharmacokinetics have been applied to the study of the behaviour of clotting factor concentrates in patients with haemophilia. Since 1980, the continuous development of innovative plasma- and rDNA-derived concentrates and the implementation of new virucidal methods in manufacturing processes has prompted us to define a standard approach to this issue. Model-based methods, based upon one or two open compartment models, were available when this work was initiated. Unfortunately, these methods are supported by very little biological data and are profoundly affected by the goodness-of-fit of the data. In contrast, the model-independent method, which is not affected by errors in fitting, provides reproducible and reliable estimates of the behaviour of clotting factor concentrates in patients with haemophilia. Further, the calculations required for the model-independent method are quite simple and can be computed using a pocket minicomputer. The need for an accurate standardization has been recognized by the Factor VIII/IX Sub-Committee which, in 1991, issued the first recommendations on the pharmacokinetic evaluation of Factor VIII/IX concentrates. A recent revision of the recommendations has been made available on the web site of the International Society on Thrombosis and Haemostasis. The most crucial changes - sample size, study design, dosages in single-dose studies, potency assessment, need for well-defined standards, optimal number of points, and most important outcomes - are discussed in this report. In addition, the model-independent and compartmental methods are described.

Intermittent injections vs. continuous infusion of factor VIII in haemophilia patients undergoing major surgery

Continuous infusion (CI) of factor VIII (FVIII) has been proved to be a safe alternative to intermittent bolus injections (BI) in haemophilia A. Most reports on CI suggest a considerable saving in FVIII compared with historical controls treated with BI, but some recent reports failed to demonstrate such an effect. The present study prospectively compared safety, efficacy and factor requirements in 43 major surgical procedures performed in severe haemophilia A patients who were treated with either BI (18 operations) or CI (25 operations). The aim was to maintain factor VIII levels above the same minimum levels. Improved safety of CI over BI was observed, despite a bias in favour of the BI group (all underwent unilateral operations, compared with 24% of the CI group who underwent bilateral operations). Higher nadir levels were found in the CI group (0.44 +/- 0.06 vs. 0.31 +/- 0.09 IU/ml; P < 0.01) with a lower incidence of dangerous drops below 0.3 IU/ml (8% vs. 44% of patients respectively; P < 0.01), and a lower drop in haemoglobin (Hb) (1.56 +/- 1.21 vs. 3.01 +/- 2.13 g/dl; P < 0.05) and blood transfusion requirements (12% vs. 39%; P < 0.01). Major bleeding complications developed in three out of 18 patients (17%) in the BI group and none of the CI group (P = 0.06). The FVIII dosage was lower by 36% in the CI group (467 +/- 104 vs. 733 +/- 126 IU/kg; P < 0.01). Had the trough factor levels been maintained at the target levels, a greater difference of 72% would probably have been observed.

Continuous infusion of intermediate-purity factor VIII in haemophilia A patients undergoing elective surgery

An open, non-randomized trial of continuous infusion therapy was conducted involving five patients with severe haemophilia A who required factor VIII (FVIII) prophylaxis for elective surgery. This was preceded by a 24-h preoperative pharmacokinetic study to characterize the pharmacokinetic parameters of each individual patient following a bolus dose of the intermediate-purity product. A retrospective matched control group was identified to allow for comparisons of FVIII usage between bolus and continuous infusion administration. A loading dose of FVIII was administered preoperatively, and the continuous infusion was started at the end of surgery and continued for 5 days. The patients' FVIII levels, vital signs, and infusion sites were monitored on a daily basis. The clearance was re-calculated on a daily basis using the FVIII activity of that day to adjust the infusion rate to achieve the desired FVIII level. The mean (CV%) pharmacokinetic parameters estimated preoperatively by noncompartmental analysis were: clearance 3.2 mL kg-1 h-1 (35.5%), volume of distribution 52.1 mL kg-1 (40.2%), mean residence time 17.4 h (23.3%), and half-life 12.7 h (23.6%). A progressive decrease in the clearance of FVIII from a mean of 3.1 mL kg-1 h-1 to 2.0 mL kg-1 h-1 (P = 0.125) over the first 5 days was observed. A therapeutically acceptable level of FVIII was systematically achieved, with the only complication being frequent thrombophlebitis. On average the patients used 19% less FVIII when compared with matched historical controls (P = 0.25). This method was found to be safe and effective in haemophilia A patients undergoing elective surgery procedures.

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

A prospective cross-over study was carried out on 19 patients with haemophilia B. comparing the pharmacokinetics of a purified factor IX concentrate prepared by metal chelate affinity chromatography (9MC) with a conventional three-factor prothrombin complex concentrate (9A). The highly purified factor IX concentrate was shown to have a half-life comparable to the PCC; the in vivo recovery of the purified concentrate was significantly greater than that of the complex (P < 0.01). The 20% change in the value of the International Standard for Factor IX Concentrate, introduced in 1988, might have been expected to lower the recovery values. However, the in vivo recovery for both concentrates was somewhat higher than reported previously, particularly in the older literature. In nine patients, serial assays for fibrinopeptide A, prothrombin fragment F1+2 and thrombin-antithrombin complexes (TAT) were performed to assess the potential thrombogenicity of the two concentrates. Evidence was obtained that there was significantly less activation of coagulation following administration of purified factor IX (9MC), as compared to the activation that occurred after the PCC.

Pharmacokinetics, thrombogenicity and safety of a double-treated prothrombin complex concentrate

The pharmacokinetic profile, the thrombogenicity and the virus safety of Preconativ, a PCC subjected both to virus removal procedure and dry-heat treatment were studied. Preconativ is produced from plasma pool, negative both for HBsAg and for antibodies to HIV. To further reduce the risk of virus transmission, the manufacturing process includes hydrophobic gel chromatography and dry-heat treatment at +68 degrees C for 48 hours. Nine patients with hemophilia B participated in a single dose, pharmacokinetic study. The decay curves of factor IX clotting activity were evaluated by model-independent methods. The Clearance and the Mean Residence Time were very similar to those previously reported for untreated PCC. The Volume of Distribution Area and In Vivo Recovery resulted inversely correlated and respectively larger and smaller than those of untreated PCC. A slight fall in platelet count and Antithrombin III level and an increase of Beta-Thromboglobulin and Fibrinopeptide A concentration were found, indicating a clear-cut activation of the coagulation process during the first hours following Preconativ administration. Seven patients (2 of the ones enrolled in the pharmacokinetic study) were completely fulfilling the SSC-ISTH criteria for virus safety prospective study. The follow up of these patients did not show any transaminases elevation or seroconversion against HBV, HCV or HIV. These findings did not change over a 3-5 year follow up in 3 out of 7 patients, repeatedly infused with Preconativ.

Adjusted dose continuous infusion of factor VIII in patients with haemophilia A

Surgical interventions in patients suffering from haemophilia A require infusions of large doses of factor VIII (F VIII) concentrates. These are expensive and may pose a burden on the immune system, which is already compromised in many haemophiliacs. F VIII is usually given as bolus injections, although there are reports on fixed dose continuous infusion. We have developed a continuous infusion programme with dosage adjusted according to daily calculation of the clearance of F VIII. Twenty-four haemophiliacs received a total of 205 d of continuous infusion with F VIII (168 d in hospital, 37 d home therapy). Eighteen patients underwent surgeries (11 elective, seven emergency) and six were treated for serious haemorrhages. We observed a significant, progressive decrease of the clearance of F VIII over the first 5 d from 3.2 (2.8-3.5) to 1.7 (1.3-1.9) ml/kg/h (median and interquartile range). The decrease of the clearance together with the fact that a continuous infusion requires less drug than bolus injections to keep the same minimal concentration, contributed to much lower doses of F VIII than reported in the literature or than required by historical controls, matched for the type of operation. Other advantages of our method are improved safety with stable activities of F VIII, lack of hazardous troughs below the haemostatic range, and the convenience, which permits ambulant therapy even when high doses of F VIII are required.

Comparative evaluation of the pharmacokinetics of three monoclonal factor VIII concentrates

Hemofil M, Monoclate HT, and Monoclate P are high-purity Factor VIII concentrates, obtained from plasma by immunoaffinity chromatography with monoclonal antibodies specific for Factor VIII (Hemofil M) or von Willebrand Factor (Monoclate HT and Monoclate P). The concentrates are subjected to virucidal treatments: a solvent/detergent method (TNBP/Na-cholate) for Hemofil M, heating in the lyophilized state and in solution (pasteurization) for Monoclate HT and Monoclate P, respectively. Since these differences in the manufacturing process might result in different in vivo characteristics of the concentrates, we compared their in vivo behavior in a cross-over, single-dose, pharmacokinetic study performed in 10 non-bleeding patients with severe hemophilia A. The experimental conditions (Factor VIII dose, number and timing of blood sampling, Factor VIII assay methods, calculation of pharmacokinetic parameters) were identical for the three products. The results showed that the clearance, the mean residence time, and the volume of distribution did not differ among the three products.

Evaluation of factor VIII pharmacokinetics in hemophilia-A subjects undergoing surgery and description of a nomogram for dosing calculations

The pharmacokinetics of factor VIII were studied in a series of 20 hemophilia-A patients undergoing surgery. Regardless of the type of operation, elimination of factor VIII was shown to be increased only in ten cases (50%) during the post-operative period. In this subgroup of patients, factor VIII half-life, measured immediately after surgery, was considerably shorter (mean = 9.6 hr, n = 10) than that determined in the same individual during the late operative period (mean = 17.8 hr, n = 10). These findings indicate that identification of patients with increased postoperative consumption of factor VIII can be of value in reducing the risk of hemorrhage in these subjects and in exposing other subjects with no postoperative increase in factor VIII clearance to less of the deficient factor. Data from 20 subjects were analyzed to construct a nomogram allowing individualized prediction of factor VIII dosing requirements. The nomogram, which is based on the "single point after a single dose" method, uses a value of factor VIII concentration measured at 10 hr after preoperative loading dose to predict the regimen producing the desired average steady-state concentration of factor VIII (30, 60, or 90 units/dl).

Biochemical and in vivo properties of commercial virus-inactivated factor VIII concentrates

The following commercial virus-inactivated factor VIII concentrates were studied in vitro: AHF-Kabi and Octonativ, KabiVitrum; Hemofil T, Hyland; Factorate HP and Monoclate, Armour; Nordiocto, Nordisk Gentofte (dry heated); Kryobulin TIM3, Immuno (steam treated); Profilate, Alpha (heated as dry material slammed in heptane); Hemate P, Behring (wet heated) and Octa-V.I., Octapharma (solvent/detergent treated). The concentration of VIII:C was lowest in AHF-Kabi, whereas it ranged from 24 to 53 IU/ml in the high purity concentrates, except for Monoclate in which it ranged from 91-128 IU/ml. All concentrates but Octa-V.I. had higher values for VIII:Ag than for VIII:C. von Willebrand factor with normal distribution of multimers could only be demonstrated in AHF-Kabi and Hemate P. In vivo studies were performed in 12 severe hemophiliacs. Recovery and half-life of VIII:C did not differ between the various concentrates. Hemate P was given to 5 patients with severe von Willebrand's disease, in all of whom a correction of the hemostatic defect was seen.

Multi-variate analysis of factors governing the pharmacokinetics of exogenous factor VIII in haemophiliacs

The pharmacokinetics of Factor VIII was evaluated by mathematical modeling in a large-scale study in 62 haemophilia-A subjects, in whom 137 plasma Factor VIII-time curves were measured during single dose (n = 87) and repeated-dose (n = 47) treatments for prophylaxis or minor bleeding episodes. The pharmacokinetic parameters [mean (SD)] estimated from single-dose curves were: clearance 3.85 ml.h-1.kg-1, volume of distribution 58.2 ml.kg-1, mean residence time 15.9 h. Parameters calculated from repeated-dose curves were: clearance 3.93 ml.h-1.kg-1, volume of distribution 61.8 ml.kg-1, and half-life 12.2 h. In patients with mild haemophilia, pharmaco-statistical analysis revealed that the endogenous synthesis of Factor VIII was constant and was not influenced by the administration of exogenous Factor VIII. The coefficient of variation for intra-individual variability of Factor VIII kinetics (estimated according to the Standard Two-Stage method) was 20.7% in single-dose curves and 23.2% in repeated-dose curves.

Single-dose pharmacokinetics of factor IX evaluated by model-independent methods

We studied the pharmacokinetic data of 13 subjects with hemophilia B treated with a single-dose of a Factor IX concentrate (Bebulin TIM2, N = 9; Preconativ, N = 4). The decay curves of Factor IX were evaluated by model-independent methods and the following pharmacokinetic parameters (mean +/- SD) were estimated: clearance (ml/h/kg) = 4.99 +/- 2.01; mean residence time (h) = 22.9 +/- 10.6; volume of distribution (ml/kg) = 99.9 +/- 35.5. The in vivo recovery (59.8% +/- 16.9%) was found to be inversely correlated with the volume of distribution. No significant difference in the pharmacokinetic parameters was found between patients treated with Preconativ and those treated with Bebulin. A model-dependent compartmental evaluation of the 13 decay curves showed that the two-compartment model was better than the one-compartment model in 7 cases (53.8%), but the improvement of fit resulting from the two-compartment model was statistically significant in only 2 cases (15.4%).

Pharmacokinetics of a new heat-treated concentrate of factor VIII estimated by model-independent methods

We evaluated the pharmacokinetic properties of Kryobulin TIM3, a new heat-treated Factor VIII concentrate which has recently become available in Europe. Twelve patients with classic hemophilia were studied. In each patient, Factor VIII was given as a single dose (ranging from 11.6 to 30.3 units/kg) after which eight serial blood samples were drawn to characterize the disappearance of Factor VIII from the plasma. Model-independent (noncompartmental) methods were used for pharmacokinetic analysis. The following pharmacokinetic parameters of Factor VIII (mean +/- SD) were estimated: clearance = 3.83 +/- 0.99 ml/h/kg; mean residence time = 15.9 +/- 4.5 h; volume of distribution at steady state = 55.6 +/- 9.3 ml/kg; in-vivo recovery = 129 +/- 29%. The pharmacokinetic parameters of Kryobulin TIM3 obtained in our study are very similar to those previously reported for the untreated concentrate. Thus, our findings suggest that the dosing guidelines previously available for the untreated concentrate need not be revised when using the treated product.