Comparison of the capacities of two prothrombin complex concentrates to restore thrombin generation in plasma from orally anticoagulated patients: an in vitro study.

BACKGROUND: Human prothrombin complex concentrates (PCCs) are used for prevention and treatment of bleeding episodes in patients under warfarin therapy. PCCs contain human factor (F) II, FVII, FIX, FX, protein C and protein S. The concentrations of these coagulation factors contained in PCCs are variable and do not reflect entirely the capacity of these drugs to correct hemostasis. Furthermore, commercially available PCCs do not have exactly the same composition, though they are all labelled and prescribed in units per kg of FIX (10-40 IU of FIX/kg). As the final product generated by PCCs is thrombin, a thrombin generation (TG) test could theoretically be used for monitoring the hemostatic correction. METHODS: TG was measured in platelet free plasma in the presence of tissue factor 5 pm and phospholipids 4 microM with a final concentration of PCC of 0-0.1-0.2-0.3-0.4-0.5-0.75-1 IU ml(-1). The activity of vitamin K-dependent coagulation factors (i.e. FII, FVII, FIX, FX, protein C and protein S) were determined for each concentration of two different PCCs available on the French market. RESULTS AND DISCUSSION: Our results showed that the addition of two different PCCs dose-dependently increased the TG capacity in patients with INR of 2-2.5-3-4 and >7 (n = 15 subjects) that reached the normal values. We also found a significant correlation between endogenous thrombin potential (ETP) and INR (Pearson test, P < 0.0001). The two PCCs improved the TG parameters differently with increasing concentrations. The difference in the correction of TG capacity observed between the two drugs could be explained by a variable increase in FX, FVII and protein C with similar doses. These results strongly suggest that TG assay could be used for monitoring the clinical efficacy of PCC and for optimizing the therapeutic regimen towards a more individualized therapy involving the type of the bleeding complications, the level of inhibition of the coagulation system and the molecule content of the PCC.

Pharmacokinetics of total immunoglobulin G and immunoglobulin G subclasses in patients undergoing replacement therapy for primary immunodeficiency syndromes.

BACKGROUND AND OBJECTIVES: Careful evaluation of the pharmacokinetic properties of a new immunoglobulin G (IgG) preparation is necessary to ensure that the product will not deviate significantly from existing products, in terms of pharmacological activity. MATERIALS AND METHODS: A prospective, open and uncontrolled trial was performed in 16 patients with primary immunodeficiency syndromes. Patients who had been under replacement therapy with licensed preparations prior to study inclusion, received 280 +/- 60 mg/kg of a solution of IgG, ready for intravenous administration, every 3 weeks for 6 months. Trough and peak plasma levels were measured immediately before and 1 h after each infusion, respectively. Pharmacokinetic parameters were calculated for total IgG and IgG subclasses. RESULTS: Total IgG, IgG1, IgG2 and IgG3 declined mono-exponentially in contrast to IgG4 which showed a bi-exponential decline. Half-lives which were highly variable among patients were similar for total IgG, IgG1 and IgG2 (35.9 +/- 10.8, 36.3 +/- 9.2, and 37.1 +/- 13.9 days, respectively) and shorter for IgG3 and IgG4 (28.6 +/- 10.4 and 15.6 +/- 4.5 days, respectively). CONCLUSIONS: The decline of IgG4 probably reflected a complex catabolic pathway specific for this subclass. As the plasma level of IgG4 is low, the decline of total IgG remained unaffected. Pharmacokinetic properties were consistent with results reported elsewhere in patients undergoing replacement therapy for primary immunodeficiency syndromes.

Competitive ELISA to evaluate the immunogenicity of double-virus-inactivated factor VIII in rabbits.

Viral inactivation is a critical step during the manufacture of factor VIII formulations for use in humans. Indeed, viral inactivation procedures may alter the three-dimensional structure of factor VIII resulting in the formation of new epitopes which, in turn, may lead to the synthesis of inhibiting antibodies, and hence to a decreased therapeutic activity. A rabbit model was used to compare the immunogenicity of a solvent/detergent (SD)-inactivated formulation with a double-inactivated (SD plus heating in solution, SDP) formulation of factor VIII. Two groups of five rabbits were immunized by six s.c. injections of each formulation. The serum of each animal was incubated with various amounts of the competing antigens, e.g. factor VIII SD or factor VIII SDP. The remaining free polyclonal antibodies were assayed by ELISA. Curves obtained with both antigens were compared for each serum. Both factor VIII SD and factor VIII SDP decreased the amount of antibodies raised to either formulation in a dose-dependent manner without observable differences. These results suggest that no new epitopes were present on factor VIII SDP as compared with factor VIII SDP as compared with factor VIII SD and that no epitope deletions occurred, supporting the view that the double-inactivation procedure does not change the immunogenicity of factor VIII SD. This model is proposed as a tool to detect changes in the immunogenicity of proteins which may be modified.

Clinical evaluation of virus safety and inhibitor incidence: statistical considerations.

The basic statistical issue in pharmacovigilance is to claim, with reasonable certainty, that the incidence of an event of interest in a population of subjects is less than a certain value. How many subjects and events must be observed before such a claim can be made? A first situation of practical importance is when a product has been on the market for some period of time, and the safety of this product regarding some outcome of interest is questioned (for instance, the viral safety of blood products). Having observed a few occurrences of the event of interest, how confident can we be that the product is responsible for an elevation of the incidence of this event compared with the baseline incidence in a reference population? This issue will increasingly need to be addressed prospectively: how many subjects need to be treated and how many events observed, to be reasonably certain that a product is safe? Multi-stage designs are appropriate to address this question, yet they do not seem popular in pharmacovigilance. Such approaches could complement the standard recommendations to assess the safety of blood products, which are adequate as a first screen against major safety problems, but wholly inadequate for the long-term surveillance of subjects at risk of rare events. It will be argued that, from a regulatory perspective, the implementation of prospective protocols for pharmacovigilance, using appropriate statistical tools, would permit a tight control of the safety of new products, while making these products available as early as possible to the patients who need them.