Single-dose pharmacokinetics of porcine factor VIII (Hyate C)

The objective was to establish the pharmacokinetic properties of porcine factor VIII (pFVIII) at three different doses in a single patient. The patient, born in 1952, had severe haemophilia A and developed an inhibitor to human FVIII (hFVIII) in 1966 aged 14 years. He was first treated with pFVIII in 1980. Apart from a short period of treatment with hFVIII in 1998 which resulted in the reappearance of the inhibitor, pFVIII has been constantly used since 1984. No inhibitor against human or porcine FVIII had been recordable over the 2-year period prior to the study. Three separate pharmacokinetic studies were performed using a washout period of 72 h and doses of 10 U kg (-1), 25 U kg (-1), or 50 U kg (-1), respectively, with sampling at preinfusion, then at 15 and 30 min and 1, 3, 6, 9, 12 and 24 h postinfusion. The FVIII levels were measured using both plasma derived one stage APTT based assay and chromogenic assay. The results were computed using a model-independent analysis and a model-dependent analysis. The respective clearances (mL h(-1)kg(-1)) at doses 50 U, 25 U or 10 U kg (-1) were 1.32, 1.33 1.8 (bioassay) and 2.54, 2.93, 9.43 (chromogenic). The respective half-lives (h) at doses 50 U, 25 U, and 10 U kg (-1) were 23.71, 16.54, 25.17 (bioassay) and 15.71, 17.39, and 10.66 (chromogenic). The respective recoveries (u dL(-1)/u kg(-1)) at doses 50 U, 25 U, and 10 U kg (-1) were 2.32, 2.44, 2.7 (bioassay) and 1.42, 1.16 and 0.9 (chromogenic). It was found that the two compartment model best fitted the curves of the bioassay and a one compartmental model best fitted the curves of the chromogenic assay. The pharmacokinetic studies are the first to be performed at different dose levels and using different assay methods for pFVIII. Using the bioassay, they show a long half-life and high recovery compared to hFVIII. The differences between the bioassay and the chromogenic assay reflect their different biological basis and are of relevance when potency labelling is performed using chromogenic assay (European Pharmacopeia).

Wear in retrieved condylar knee arthroplasties. A comparison of wear in different designs of 280 retrieved condylar knee prostheses

The plastic components of 280 retrieved unicondylar and total knee arthroplasties were studied. Wear was visually scored using a relative ranked data method. Although wear on the components was highly variable, several conclusions could be drawn regarding the nature and causes. Wear was associated more with the medial than the lateral condyle. Delamination was the most severe type of wear and occurred in short (< 5 year)-, medium (5-10 years)-, and long (> 10 years)-term retrievals. In the short term, delamination wear was associated with hot pressing of the tibial plastic or with fracture of the tibial baseplate. For a single design, a significant difference in the amount of delamination on hot-pressed and non-hot-pressed tibial components was observed. In medium- and long-term retrieved specimens of the designs with moderately high conformity, delamination wear was associated with restriction of rotational movement of the femoral component or with abrupt changes in the radius of the tibial component. In flatter, less conforming designs, wear was associated with laxity, such that the polyethylene delaminated toward the edges of the tibial component. Wear attributed to cement abrasion or entrapment occurred on the more conforming designs. Delamination was associated with the presence of fusion defects in the polyethylene but could also occur in the absence of such defects. That delamination was the principal were type and that this is caused by a fatigue mechanism mean that the incidence of failure could accelerate considerably over follow-up periods beyond 10 years. Designs of moderate conformity without abrupt changes in radii may prolong the duration of plastic tibial components before serious delamination occurs.

Pharmacokinetic in vivo comparison using 1-stage and chromogenic substrate assays with two formulations of Hemofil-M

In a study to demonstrate the safety and pharmacokinetics (half-life and recovery) of two different method M purified AHF (Hemofil-M) concentrates processed in the USA and Spain, two different methods of factor VIII assay (one-stage clotting and chromogenic) have been compared in vivo. The study was a single centre blinded, randomised, crossover study. Twelve patients with severe haemophilia A (VIII:C < 2 u/dl) were divided into two subgroups of six. None had received factor VIII concentrate within 48 h preceding the study. Twenty-four pharmacokinetic studies were performed in the 12 patients. Each subgroup received two different lots of study material (US and Spanish) at a dose of 50 u/kg seven days apart. A second randomisation was nominal potency, high: 1000 u or mid: 500 u per vial. The potency label was a one-stage clotting assay using the mega I standard. A standard pharmacokinetic study was performed over 24 h and each blinded sample was analysed in duplicate by a one-stage clotting (aPTT) and a chromogenic (Chromogenix AB; CS) assay at the Royal Free and NIBSC. Pharmacokinetic modelling was performed. The mean label for Hemofil-M using the chromogenic substrate assay was 79% that using the one stage assay (Mega I standard). The recovery was 17-28% higher measured by chromogenic compared to the clotting assay. Since most clinicians use the clotting assay, potency labelling using the chromogenic assay, will overestimate predicted Hemofil-M recovery by as much as 25%.

The use of intermediate-purity clotting factor concentrates and HIV disease progression in men with haemophilia

On the basis of evidence from the immune systems of patients with haemophilia infected with HIV, patients in the UK have been switched to high-purity clotting factor concentrates. However, there is very little information currently available on the effect of intermediate-purity clotting factor concentrates on progression of HIV disease. Among 99 HIV-positive men with severe factor VIII deficiency registered at The Royal Free Hospital Haemophilia Centre, a 100 IU kg(-1) increase in the yearly amount of concentrate received did not appear to be associated with more rapid progression to AIDS, death or to a low CD4 count. However, the use of total concentrate usage may mask a more subtle effect of specific concentrate contaminants on the progression of HIV disease.

Comparison of immunodeficiency and AIDS defining conditions in HIV negative and HIV positive men with haemophilia A

OBJECTIVE

To investigate the hypothesis that high usage of clotting factor concentrate, rather than HIV infection, is the cause of immunodeficiency and AIDS in men with haemophilia.

DESIGN

A comparison of AIDS defining conditions and CD4 counts in HIV positive and HIV negative patients with haemophilia matched for usage of clotting factor concentrate.

SETTING

A comprehensive care haemophilia centre.

SUBJECTS

17 HIV positive and 17 HIV negative male patients with haemophilia A (age range 12-60 at beginning of study period) who had received similar amounts of clotting factor concentrate yearly over the years 1980-90.

MAIN OUTCOME MEASURES

Clinical events listed as AIDS defining in the Centers for Disease Control AIDS definition; CD4 lymphocyte counts; death.

RESULTS

Of 108 HIV positive male patients with haemophilia A, only 17 could be matched to an HIV negative patient. This was due to the much higher average usage of factor VIII in the HIV positive group. Between 1980 and 1990, 16 clinical events occurred in nine of the 17 HIV positive patients. No event occurred in the 17 HIV negative patients. In each pair the mean CD4 count during follow up was, on average, 0.5 x 10(9)/l lower in the HIV positive patient.

CONCLUSION

These data reject the hypothesis that high usage of clotting factor concentrate, rather than HIV infection, is the cause of immunodeficiency and AIDS in men with haemophilia.