Clinical Pharmacology for Corifact
Mechanism Of Action
CORIFACT (FXIII) is an endogenous plasma glycoprotein consisting of two A-subunits and two B-subunits. FXIIIa promotes cross-linking of fibrin during coagulation and is essential to the physiological protection of the clot against fibrinolysis. FXIIIa is a transglutaminase enzyme that catalyzes the cross-linking of the fibrin α- and g-chains for fibrin stabilization and renders the fibrin clot more elastic and resistant to fibrinolysis.2,3 FXIIIa also cross-links a2-plasmin inhibitor to the a-chain of fibrin, resulting in protection of the fibrin clot from degradation by plasmin. Cross-linked fibrin is the end result of the coagulation cascade, and provides tensile strength to a primary hemostatic platelet plug.3
The B-subunits in plasma have no enzymatic activity, and function as carrier molecules for the A-subunits. They stabilize the structure of the A-subunits and protect them from proteolysis.
Pharmacodynamics
Administration of CORIFACT to patients with congenital FXIII deficiency replaces missing or low levels of coagulation Factor XIII, enabling a temporary correction of the factor deficiency and correction of bleeding tendencies. There are no markers that can quantitatively assess the in vivo pharmacodynamics of FXIII. The results of standard coagulation (clot timebased) tests are normal in FXIII deficient patients as it is the quality of the clot that is affected. A qualitative assay of clot suitability is used as an indicator of FXIII deficiency; when performed correctly the test is positive only when the FXIII activity in the sample is close to zero. Thromboelastography can also be affected by FXIII deficiency.
Pharmacokinetics
A 12-week prospective, open-label, multicenter pharmacokinetic and safety study was conducted in 7 females and 7 males with congenital FXIII deficiency, ranging in age from 5 to 42 years (3 children, 2 adolescents, 9 adults). One adult male did not complete the pharmacokinetic study.
Each subject received 40 units per kg CORIFACT intravenously every 28 days for a total of three doses administered at approximately 250 units per minute. Blood samples for doses 1 and 2 were drawn from patients to determine the FXIII activity level at baseline and 30 and 60 minutes after the infusion. Following the infusion of the third dose of CORIFACT, blood samples were drawn at regular intervals up to 28 days to determine the pharmacokinetic parameters. The mean increase in FXIII activity levels was 83% with a range of 48 to 114% over the baseline after the third dose. The pharmacokinetic parameters based on baseline adjusted FXIII activity (Berichrom assay) are shown in Table 5.
Table 5: Pharmacokinetic Parameters (n=13) by Berichrom Assay Method - Baseline Adjusted Values
| Parameters | Mean ±SD |
| AUC ss, 0-inf (units•hr/mL) | 184.0 ±65.78 |
| Css,max (units/mL)* | 0.9 ±0.20 |
| Css,min (units/mL)* | 0.05 ±0.05 |
| Tmax (hr) | 1.7 ±1.44 |
| Half-life [days] | 6.6 ±2.29 |
| CL [mL/hr/kg] | 0.25 ±0.09 |
| Vss [mL/kg] | 51.1 ±12.61 |
| MRT [days] | 10.0 ±3.45 |
AUC ss, (0-inf) = Area under the plasma concentration curve from time 0 to infinity at steady state * 100% activity corresponds to 1 unit/mL Css, max: Peak concentration at steady state Css, min: Trough concentration at steady state Tmax: Time to peak concentration CL: Clearance Vss: Volume of distribution at steady state MRT = Mean residence time SD = Standard deviation |
Clinical Studies
Pharmacokinetic Study
The accelerated approval of CORIFACT was based on a pharmacokinetic study in 13 subjects with congenital FXIII deficiency evaluating three doses at 40 units per kg every 28 days for each subject. Maintaining FXIII activity trough level between 5%-20% is predicted to provide clinical benefit. Twelve out of thirteen subjects (92%) attained trough FXIII levels of ≥ 5%. based on standard Berichrom assay [see CLINICAL PHARMACOLOGY].
The post marketing efficacy and safety trial was a prospective, multicenter, open-label study conducted in 41 subjects who received routine prophylactic treatment (40 U/kg every 28 days for 52 weeks) for congenital FXIII deficiency, was to verify the clinical benefit of CORIFACT by showing correlation between trough levels of FXIII activity and bleeding outcomes. The clinical benefit of CORIFACT was also demonstrated by comparing the incidence of bleeding in CORIFACT-treated subjects to historical control with congenital FXIII deficiency.
This study included 18 subjects (44%) who were less than 16 years of age and 23 subjects (56%) who were ≥16 to <65 years. Two subjects were 1 month to <2 years of age, 8 subjects were 2 years to <12 years, and 8 subjects were 12-16 years of age.
The incidence of spontaneous bleeding episodes requiring treatment was evaluated. Treatment was defined as an administration of a FXIII-containing product to treat the bleeding episode. None of the 5 subjects who experienced a spontaneous bleeding episode (2 nose bleeds, 2 rectal bleeds, and 1 episode of hematuria associated with a urinary tract infection, and an indwelling urinary catheter) required treatment with a FXIIIcontaining product.
An annualized bleeding rate of 0 episodes per subject per year for spontaneous bleeding was established when compared to a historical annualized bleeding rate of 2.5 episodes per subject per year in patients receiving on-demand treatment of acute bleeding in patients with congenital FXIII deficiency.4
Eight bleeding episodes secondary to trauma, and one associated with surgery were also reported during the 52 weeks of the trial. In the eight bleeding episodes secondary to trauma, six did not require treatment with a FXIII-containing product, and two were successfully treated with a FXIII-containing product (one was treated with CORIFACT and one with plasma).
The prophylactic administration of Factor XIII Concentrate (Human) every 28 days in subjects with congenital FXIII deficiency achieved mean FXIII activity levels between 5% and 20%. FXIII activity was maintained at ≥5% in ≥97% of subjects and ≥10% in ≥85% of subjects. Of the 533 doses administered to 41 subjects, dose adjustment was required on only eight occasions, supporting that 40 U/kg every 28 days is the appropriate dose for the majority of patients.
Five subjects underwent surgical procedures, four were elective and one was an emergency. Of the four elective surgeries, three subjects received CORIFACT prior to surgery (0 to 7 days prior to surgery) with no post-operative bleeding. One subject who received CORIFACT 7 days prior to surgery experienced bleeding post-extraction of all four wisdom teeth. The bleeding was stopped four hours after the oral surgery with an additional dose of CORIFACT (50% of the subject’s routine dose). One subject who required emergency surgery was pre-treated with plasma.
REFERENCES
2. Lauer P, Metzner HJ, Zettlmeissl G, Li M, et al. Targeted Inactivation of the Mouse Locus Encoding Coagulation Factor XIII-A: Hemostatic Abnormalities in Mutant Mice and Characterization of the Coagulation Deficit. Thromb Haemost. 2002;88:967-74.
3. Dardik R, Loscalzo J, Inbal A. Factor XIII (FXIII) and Angiogenesis. J Thromb Haemost. 2006;4:19-25.
4. Lusher J, Pipe SW, Alexander S, Nugent D. Prophylactic therapy with Fibrogammin P is associated with a decreased incidence of bleeding episodes: a retrospective study. Haemophilia. 2009;1-6.