Pharmacokinetics of von Willebrand factor and factor VIIIcoagulant activity in patients with von Willebrand diseasetype 3 and type 2

D. MENACHE

American Red Cross National Headquarters, Medical Affairs, Plasma Operations, Arlington, VA, USA

Introduction

The published data on the pharmacokinetics of vonWillebrand factor (vWF) are limited [1±4] andconsist for the most part of unanalysed data. Inaddition, there is no formal analysis of the factor VIII(FVIII) pharmacokinetics as a consequence of theinfusion of large amounts of FVIII with the productsstudied. The importance of vWF in stabilizing thecirculating FVIII is well established and in theabsence of vWF the FVIII has a very short half-life[2,5,6]. Following the transfusion of products con-taining both FVIII and vWF into patients with vonWillebrand disease the half-life of FVIII:C seems tobe longer than when these products are transfused topatients with haemophilia A. The availability of avWF product with a very low content of FVIII forreplacement therapy in patients with von Willebrand

disease has provided the opportunity to evaluate thepharmacokinetics of vWF and FVIII:C in patientswith von Willebrand disease type 3 and von Wille-brand disease type 2.

Materials and methods

Patient selection

Patients' inclusion criteria were those with hereditaryvon Willebrand disease not responsive to DDAVP.Patients were excluded from the study if they hadevidence of an inhibitor to vWF; had clinical man-ifestation of haemorrhage; had received DDAVPwithin 10 days prior to enrolment; or were pregnantor nursing. After obtaining Institutional ReviewBoard (IRB) approval and written informed consentnine patients with von Willebrand disease type 3; sixwith type 2B; one with type 2A; and one patient withtype 1/2N entered the study. All patients with vonWillebrand disease type 3 had non-detectable levelsof RCoF. With the exception of one patient who had

Summary. Nine patients with von Willebrand diseasetype 3, six with type 2B, one with type 2A, and onepatient with type 1/2N were infused with one dose of�50 or 100 IU ristocetin cofactor activity (RCoF) perkg body weight of von Willebrand factor (vWF)(Human), a product with a very low content of factorVIII (FVIII). Blood samples were collected over 96 h.The data for RCoF and vWF antigen (vWF:Ag) were®tted to a 1-compartment model decay. The data forFVIII:C were ®tted to a model with a linear time`synthesis' term and a 1-compartment decay. Resultsin von Willebrand disease type 3 patients (ninepatients; 10 infusions) indicated a volume of distri-bution of 39.9 and 39.8 mL kg)1 for RCoF andvWF:Ag, respectively. The FVIII:C rate of synthesis

was 6.4 U dL)1 h)1 (range: 4.4±8.8). The decay ratesfor FVIII:C, RCoF, and vWF:Ag were 0.041 (h)1)[t1/2: 16.9 h]; 0.061 (h)1) [t1/2: 11.3 h] and 0.006(h)1) [t1/2: 12.4 h], respectively. In patients with vonWillebrand disease type 2 (n � 8) the RCoF meanvolume of distribution was 46 mL kg)1. The factorVIIIC mean rate of synthesis was 5.5 U dL)1h)1 andthe decay rate 0.043 (h)1) [t1/2: 16.1 h]. The rate ofdecay for RCoF and vWF:Ag were 0.050 (h)1) [t1/2:13.9 h] and 0.044 (h)1) [t1/2: 15.7 h], respectively.

Keywords: pharmacokinetics of FVIII, pharmaco-kinetics of vWF, FVIII synthesis, FVIII decay, vWFdecay.

Correspondence: Dr D. Menache, 7808 Maple Ridge Road,Bethesda, MD 20814, USA. Tel: �1 301 6560993; Fax: �1301 9865178.

Haemophilia (1998), 4 (Suppl. 3), 44±47

44 Ó 1998 Blackwell Science Ltd

faint dimers and 6 U dL)1 von Willebrand factorantigen (vWF:Ag) and FVIII coagulant activity(FVIII:C), the remaining eight patients had non-detectable vWF:Ag and levels of FVIII:C rangingbetween 3 and 5 U dL)1. Patients with type 2B hadRCoF levels ranging from < 3±66 U dL)1; vWF:Agfrom 18 to 82 U dL)1 and FVIII:C from 31 to 79U dL)1. No high molecular weight multimers(HMWM) were noted. The patient with type 2Ahad < 3 U dL)1 RCoF with 17 U dL)1 vWF:Ag and7.6 U dL)1 FVIII:C. No HMWM were noted andthere was an increase in dimers. The patient with vonWillebrand disease type 1/2N had normal multimersand 16; 14; and 13 U dL)1 RCoF, vWF:Ag, andFVIII:C, respectively.

Product

von Willebrand factor (Human) was used in thestudy under an Investigational New Drug Applica-tion (IND). This product is a solvent and detergenttreated preparation of von Willebrand factor (vWF)derived from blood collected by the American RedCross Blood Services from volunteer US donors, andmanufactured by Laboratoire FrancËais du Fraction-nement et des Biotechnologies (LFB), Les Ulis,France, for exclusive use by the American Red Cross.Separation of FVIII from vWF is achieved by ionexchange chromatography [7,8]. Six lots of productwere used. The RCoF activity ranged from 131 to175 IU mg)1 protein, and the ratio of RCoF tovWF:Ag ranged from 0.91 to 1.40. Each lot con-tained no more than 10 IU FVIII:C per 100 IU RCoF.

Protocol

Patients were administered one infusion of vonWillebrand factor (Human) at an approximate doseof either 50 or 100 IU RCoF kg)1 body weight. Fivepatients with von Willebrand disease type 3; twowith type 2B; and one with type 2A received 50 IURCoF kg)1; while ®ve patients with von Willebranddisease type 3; four with type 2B and one with type1/2N received 100 IU kg)1. Blood samples werecollected pre infusion and at 0.25, 1, 4, 8, 24, 72and 96 h post-infusion. Each sample was tested forFVIII:C, RCoF, vWF:Ag and multimers.

Assays

All assays were performed by the Blood Center ofSoutheastern Wisconsin, Milwaukee, WI, USA onplasma samples shipped frozen to the laboratory.

Sample collection and processing as well as themethods used to assay FVIII:C, RCoF, vWF:Ag andmultimer analysis were previously published [9].

Data analysis

A non-linear square analysis was performed usingthe Micromath Scientist program (Micromath Sci-enti®c Software, Salt Lake City, UT, USA).

The data points for FVIII:C were ®tted using theformula:

FVIII:C � A0 � �A1 � k1t� exp�ÿk2t�

where k1 � synthesis rate of FVIII:C (U dL)1 h)1);k2 � decay rate of FVIII:C (h)1); A0 � infusedFVIII:C. For patients with von Willebrand diseasetype 3 the pre-infusion FVIII:C was assumed to bethe baseline value and the 15 min postinfusionincrement was used to correct for the FVIII:C presentin the product. Because in von Willebrand diseasetype 2 patients the FVIII:C levels at 96 h postinfusionnever reached the baseline value, the 96 h time pointwas taken as the base level. The model used assumesa constant rate of FVIII synthesis (release in thecirculation) and assumes that the circulating level ofFVIII is independent of the level of vWF. The FVIII:Cdecay constant was calculated using the 1-compart-ment model outlined above and for patients with vonWillebrand disease type 3 the data was also calcu-lated without correcting for synthesis from 24 to96 h postinfusion.

The data points for the decay of RCoF andvWF:Ag were ®tted to the expression:

vWF � exp �ÿk3 t�:

Results

Following infusion, the volume of distribution ofRCoF was 46 mL kg)1 in patients with type 2(n � 8); and 39.9 mL kg)1 in von Willebranddisease type 3 (n � 10). The vWF:Ag and theRCoF declined in a logarithmic fashion. TheFVIII:C levels increased progressively with the peaklevels between the 8-h and 24-h sample. Thisincrease was followed by a gradual decay aspredicted by the model.

Except for one patient with type 2B all patients'data were ®tted to the equation shown above.Figure 1 and Fig. 2 compare the experimental datafor RCoF; vWF:Ag and FVIII:C with the proposedmodel in one patient with von Willebrand diseasetype 3 (Fig. 1) and in one patient with von Wille-brand disease type 2 (Fig. 2).

PHARMACOKINETICS OF VON WILLEBRAND DISEASE AND FVIII:C 45

Ó 1998 Blackwell Science Ltd Haemophilia (1998), 4 (Suppl. 3), 44±47

In type 3 von Willebrand disease patients (ninepatients; 10 infusions) the FVIII:C rate of synthesisranged from 4.4 to 8.8 U dL)1 h)1 and the decayfrom 0.034 to 0.052. The decay rates for RCoF andvWF:Ag ranged from 0.038 to 0.1 (h)1) and from0.040 to 0.083 (h)1), respectively. The calculatedmean rate of FVIII:C synthesis and decay as well asthe mean decay of RCoF and vWF:Ag in patientswith von Willebrand disease type 3 are shown inTable 1.

In patient with von Willebrand disease type 2(n � 8) the FVIII:C rate of synthesis ranged from2.1 to 9.1 U dL)1 h)1 and the FVIII:C decay from0.030 to 0.064 (h)1). The rate of decay for RCoF andvWF:Ag ranged from 0.035 to 0.080 (h)1) and0.015±0.057 (h)1), respectively. The calculated meanrate of FVIII:C synthesis and decay as well as themean decay of RCoF and vWF:Ag in patients withvon Willebrand disease type 2 are shown in Table 1.

Discussion

The availability of a vWF product with a very lowFVIII content has allowed estimation of the pharma-cokinetics of the vWF and of FVIII in patients withvon Willebrand disease. Individual test results forpatients with von Willebrand disease type 3 andtype 2 have been published [9,10]. Taking intoconsideration the rate of synthesis (release in thecirculation) of FVIII, the half-life of the protein issimilar to that seen in patients with haemophilia A.These results con®rm the hypothesis of Biggs andMatthews [1] who postulated that when correctingfor FVIII synthesis the half-life of FVIII would besimilar in patients with von Willebrand disease and

in those with haemophilia A. Calculating the FVIII:Cdecay without correcting for `synthesis' using a 1-compartment model from 24 to 96 h postinfusion,the mean FVIII:C decay in patients with von Wille-brand disease type 3 was much slower and the half-life of approximately 40 h was consistent with theresults obtained by Goudemand et al. [11] using asimilar product. In von Willebrand disease type 3 themean decay of vWF is 0.061 (h)1) for RCoF and0.056 (h)1) for the vWF:Ag while in von Willebranddisease type 2 the mean decay is 0.050 (h)1) forRCoF and 0.044 (h)1) for vWF:Ag. The slightlyfaster decay of the RCoF compared to the vWF:Ag isseen in the published data for other products [3].This is consistent with the viewpoint that the largermultimers are cleared or are proteolysed somewhatmore rapidly than are the smaller multimers withlower RCoF activity.

Table 1. Pharmacokinetics of von Willebrand factor and factor

VIII coagulant activity in type 3 von Willebrand disease (n � 10)

and in type 2 von Willebrand disease (n � 8).

Synthesis Decay Half-life

(U dL)1h)1) (h)1) (h)

type 3

FVIII:C 6.4 0.041 16.9

Apparent t� 40

RCoF 0.061 11.3

vWF:Ag 0.056 12.4

type 2

FVIII:C 5.5 0.043 16.1

RCoF 0.050 13.9

vWF:Ag 0.044 15.7

Fig. 1. Type 3 von Willebrand disease patient administered von

Willebrand factor (Human) at a dose of 100 IU RCoF kg)1. Filled

triangles: experimental data for RCoF; solid line: ®tted curve for

RCoF. vWF:Ag data superimposable to RCoF data are not shown.

Filled squares: experimental FVIII:C data; solid line: ®tted curve

for FVIII:C.

Fig. 2. Type 2 von Willebrand disease patient administered with

von Willebrand factor (Human) at a dose of 100 IU RCoF kg)1.

Filled triangles: experimental data for RCoF; solid line ®tted curve

for RCoF. Filled squares: experimental FVIII:C data; solid line:

®tted curve for FVIII:C. Solid circles: experimental vWF:Ag data;

solid line: ®tted curve for vWF:Ag.

46 D. MENACHE

Haemophilia (1998), 4 (Suppl. 3), 44±47 Ó 1998 Blackwell Science Ltd

Analysis of the pharmacokinetic data according tothe proposed model indicates that the repetitiveadministration of a vWF product (devoid of FVIII)will result in a continuous rise in FVIII up to aplateau whose height depends on the rate of releaseof the FVIII in the circulation.

Acknowledgments

The author wishes to acknowledge the contributionof David L. Aronson; Robert R. Montgomery and hisLaboratory, The Blood Center of Southeastern Wis-consin and the Department of Pediatrics, MedicalCollege of Wisconsin, Milwaukee, Wisconsin; FredDarr and N. David Kennedy, American Red CrossNational Headquarters, Washington DC for dataanalysis and data collection. This clinical investiga-tion study was conducted by the von WillebrandFactor (Human) Cooperative Study Group whichincludes the following clinical investigators: Joan C.Gill; Craig M. Kessler; Cindy L. Leissinger; JeanneM. Lusher; Pradyumna D. Phatak; Amy D. Shapiro;Arthur R. Thompson and Gilbert C. White II.

The diligent cooperation of the staff in the conductof the study is also acknowledged.

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