Ceprotin (Protein C) - Description and Clinical Pharmacology

DESCRIPTION

CEPROTIN [Protein C Concentrate (Human)] is manufactured from human plasma purified by a combination of filtration and chromatographic procedures, including a column of immobilized mouse monoclonal antibodies on gel beads. See WARNINGS/PRECAUTIONS: Transmission of Infectious Agents .

The manufacturing process for CEPROTIN includes processing steps designed to reduce the risk of viral transmission. Screening against potentially infectious agents begins with the donor selection process and continues throughout plasma collection and plasma preparation. Each individual plasma donation used in the manufacture of CEPROTIN is collected only at FDA-approved blood establishments and is tested by FDA licensed serological tests for Hepatitis B Surface Antigen (HBsAg), and for antibodies to Human Immunodeficiency Virus (HIV-1/HIV-2) and Hepatitis C Virus (HCV) in accordance with U.S. regulatory requirements. As an additional safety measure, plasma pools for manufacturing are tested for the presence of HIV-1 and HCV by FDA licensed Nucleic Acid Testing (NAT) and found negative.

To further improve the margin of safety, two dedicated, independent and effective virus inactivation steps (Polysorbate 80 [P80] treatment and vapor heating) have been integrated into the manufacturing process in addition to other purification steps such as immunoaffinity chromatography.

Comprehensive virus clearance studies have been performed for the following steps: P80 treatment alone or coupled with an ion exchange chromatography step (IEX I), immunoaffinity chromatography (IAX) and vapor heating. In each study, the validity of the downscaled process has been confirmed by measuring process and biochemical parameters and comparing these with data from the large-scale manufacturing process. Where applicable (i.e. for P80 treatment and for vapor heating), the robustness of virus clearance has also been investigated by adjusting critical process parameters to levels least favorable for virus inactivation (e.g. temperature and incubation time for vapor heating).

Virus clearance studies for CEPROTIN have demonstrated that the process provides for a robust overall virus clearance capacity. A summary of log₁₀ virus reduction factors per virus and manufacturing step is presented in the Table 2.

Table 2: Summary of Mean Log₁₀ Virus Reduction Factors for the CEPROTIN Manufacturing Process

Manufact- uring Step	HIV-1	HCV Model Viruses		PRV	HAV	MMV
		BVDV	TBEV
P80 Treatment	>5.1	>4.7	n.d.	2.5 1	>3.8	1.4
IAX	5.7	n.d.	4.8	5.4	3.1	3.6
Vapor Heating	4.6	>5.9	n.d.	5.9	>4.2	1.2

CEPROTIN is supplied as a sterile, white or cream colored, lyophilized powder for IV injection. It has a pH between 6.7 and 7.3 and an osmolality not lower than 240 mosmol/kg. One International Unit (IU) of protein C corresponds to the amidolytically measured activity of protein C in 1 mL of normal plasma. The potency (IU) is determined using a chromogenic substrate method referenced against the World Health Organization (WHO) International Standard (86/622).

CLINICAL PHARMACOLOGY

Mechanism of Action

Protein C is the precursor of a vitamin K-dependent anticoagulant glycoprotein (serine protease) that is synthesized in the liver. See DOSAGE AND ADMINISTRATION: Initiation of Vitamin K Antagonists . It is converted by the thrombin/thrombomodulin-complex on the endothelial cell surface to activated Protein C (APC). APC is a serine protease with potent anticoagulant effects, especially in the presence of its cofactor protein S. APC exerts its effect by the inactivation of the activated forms of factors V and VIII, which leads to a decrease in thrombin formation. APC has also been shown to have profibrinolytic effects.

The Protein C pathway provides a natural mechanism for control of the coagulation system and prevention of excessive procoagulant responses to activating stimuli. A complete absence of protein C is not compatible with life. A severe deficiency of this anticoagulant protein causes a defect in the control mechanism and leads to unchecked coagulation activation, resulting in thrombin generation and intravascular clot formation with thrombosis.

Pharmacodynamics

In clinical studies, the intravenous administration of CEPROTIN demonstrated a temporary increase, within approximately half an hour of administration, in plasma levels of protein C. Replacement of protein C in protein C-deficient patients is expected to control or, if given prophylactically, to prevent thrombotic complications.

Pharmacokinetics

Table 3 provides pharmacokinetic results for asymptomatic and symptomatic subjects with protein C deficiency.

Table 3: Pharmacokinetics of CEPROTIN in Subjects with Severe Congenital Protein C Deficiency

Cmax = Maximum concentration after infusion; T max = Time at maximum concentration; AUC 0-Infinity = Area under the curve from 0 to infinity; MRT = Mean residence time; and Incremental recovery = Maximum increase in Protein C concentration following infusion divided by dose
PK parameter	N	Median	95% CI for median	Min	Max
Cmax [IU/dL]	21	110	106 to 127	40	141
Tmax [h]	21	0.50	0.50 to 1.05	0.17	1.33
Incremental recovery [(IU/dL)/(IU/kg)]	21	1.42	1.32 to 1.59	0.50	1.76
Initial half-life [h]	21	7.8	5.4 to 9.3	3.0	36.1
Terminal half-life [h]	21	9.9	7.0 to 12.4	4.4	15.8
Half-life by the non-compartmental approach [h]	21	9.8	7.1 to 11.6	4.9	14.7
AUC0-Infinity [IU*h/dL]	21	1500	1289 to 1897	344	2437
MRT [h]	21	14.1	10.3 to 16.7	7.1	21.3
Clearance [dL/kg/h]	21	0.0533	0.0428 to 0.0792	0.0328	0.2324
Volume of distribution at steady state [dL/kg]	21	0.74	0.70 to 0.89	0.44	1.65

The protein C plasma activity was measured by chromogenic and/or clotting assay. The maximum plasma concentrations (C_max) and area under the plasma concentration-time curve (AUC) appeared to increase dose-linearly between 40 and 80 IU/kg. The median incremental recovery was 1.42 [(IU/dL)/(IU/kg)] after intravenous administration of CEPROTIN. The median half-lives, based on non-compartmental method, ranged from 4.9 to 14.7 hours, with a median of 9.8 hours. In patients with acute thrombosis, both the increase in protein C plasma levels as well as half-life may be considerably reduced. No formal study or analysis has been performed to evaluate the effect of covariates such as race and gender on the pharmacokinetics of CEPROTIN.

The pharmacokinetic profile in pediatric patients has not been formally assessed. Limited data suggest that the pharmacokinetics of CEPROTIN may be different between very young children and adults. The systemic exposure (C_max and AUC) may be considerably reduced due to a faster clearance, a larger volume of distribution, and/or a shorter half-life of protein C in very young children than in older subjects. This fact must be considered when a dosing regimen for children is determined. Doses should be individualized based upon protein C activity levels. See DOSAGE AND ADMINISTRATION: Protein C Activity Monitoring .

NONCLINICAL TOXICOLOGY

Carcinogenesis, Mutagenesis, Impairment of Fertility

Protein C contained in CEPROTIN is a normal constituent of human plasma and acts like endogenous protein C. Studies in heterologous species to evaluate carcinogenicity, reproductive toxicology and developmental toxicology have not been performed.

CEPROTIN has not demonstrated mutagenic potential in the Salmonella Thyphimurium reverse mutation assay (Ames test).

Animal Toxicology and/or Pharmacology

Safety Pharmacology:

Cardio-respiratory studies performed in dogs evaluating mean arterial pressure, cardiac output, systemic vascular resistance, heart rate, QT interval changes, pulmonary artery pressure, respiratory rate and respiratory minute volume demonstrated no adverse effects at a maximum dose of 500 IU/kg. Anaphylactoid reactions as determined by measurement of bronchospastic activity in guinea pigs demonstrated no adverse effects at the maximum dose of 300 IU/kg. Thrombogenic potential was evaluated in rabbits using the Wessler stasis model and demonstrated no adverse effects at 200 IU/kg. Overall, safety pharmacology studies evaluating cardio-respiratory function, acute dose anaphylactoid potential and thrombogenicity demonstrated no adverse effects in a range of doses from 1.6 to 4.2 times the maximum single human dosage per kilogram body weight.

Acute Dose Toxicity: 

Toxicity testing in rats and mice following single dosing of 2000 IU/kg or 1500 IU/kg, respectively, demonstrated no adverse clinical effects or gross pathology at 14 days post dosing.

Repeated Dose Toxicity:

Studies were not conducted to evaluate repeated-dose toxicity in animals. Prior experience with CEPROTIN has suggested immunogenic response in heterologous species following repeated dosing of this human derived protein. Thus, the long-term toxicity potential of CEPROTIN following repeated dosing in animals is unknown.

Local Tolerance Testing:

Investigation of route of injection tolerance demonstrated that CEPROTIN did not result in any local reactions after intravenous, intra-arterial injections of 500 IU/kg (5 mL) and paravenous injections of 100 IU/kg (1 mL) in rabbits.

Citrate Toxicity:

CEPROTIN contains 4.4 mg of Trisodium Citrate Dihydrate (TCD) per mL of reconstituted product. Studies in mice evaluating 1000 IU vials reconstituted with 10 mL vehicle followed by dosing at 30 mL/kg (132 mg/kg TCD) and 60 mL/kg (264 mg/kg TCD) resulted in signs of citrate toxicity (dyspnea, slowed movement, hemoperitoneum, lung and thymus hemorrhage and renal pelvis dilation).

CLINICAL STUDIES

Pivotal Study

This was a multi-center, open-label, non-randomized, phase 2/3 study in 3 parts which evaluated the safety and efficacy of CEPROTIN in subjects with severe congenital protein C deficiency for the (on-demand) treatment of acute thrombotic episodes, such as purpura fulminans (PF), warfarin-induced skin necrosis (WISN) and other thromboembolic events, and for short-term or long-term prophylaxis. Eighteen subjects (9 male and 9 female), ages ranging from 0 (newborn) to 25.7 years participated in this study.

The clinical endpoint of the study was to assess whether episodes of PF and/or other thromboembolic events were treated effectively, effectively with complications, or not treated effectively. Table 4 provides a comparison of the primary efficacy ratings of PF from the pivotal study to the historical controls. Inadequate data is available for treatment of WISN.

Table 4: Comparison of Primary Efficacy Ratings of Episodes of Purpura Fulminans in the Protein C Concentrate (Human) Pivotal Study to Historical Controls

N = Number of episodes
		Protein C Concentrate (Human)		Historical Controls
Episode Type	Primary Efficacy Rating	N	%	N	%
Purpura Fulminans	Effective	17	94.4	11	52.4
	Effective with Complication	1	5.6	7	33.3
	Not Effective	0	0.0	3	14.3
	Total	18	100.0	21	100.0

Of 18 episodes of PF (6 severe, 11 moderate, 1 mild) treated with CEPROTIN for the primary efficacy rating, 17 (94.4%) were rated as effective, and 1 (5.6%) was rated as effective with complications; none (0%) were rated not effective. When compared with the efficacy ratings for 21 episodes of PF (historical control group), subjects with severe congenital protein C deficiency were more effectively treated with CEPROTIN than those treated with modalities such as fresh frozen plasma or conventional anticoagulants.

Table 5 provides a summary of the secondary treatment ratings for treatment of skin lesions and other thrombotic episodes from part one of the study.

Table 5: Summary of Secondary Treatment Ratings for Treatment of Skin Lesions and Other Thrombotic Episodes - Protein C Concentrate (Human) Pivotal Study Part 1

N = Number of episodes
	Purpura Fulminans Skin Necrosis								Other Thrombotic Events		Total
	Mild		Moderate		Severe		Total		Total
Rating Category	N	%	N	%	N	%	N	%	N	%	N	%
Excellent	1	5.6	7	38.9	5	27.8	13	72.2	4	80.0	17	73.9
Good	0	0.0	4	22.2	0	0.0	4	22.2	1	20.0	5	21.7
Fair	0	0.0	0	0.0	1	5.6	1	5.6	0	0	1	4.3
Total	1	5.6	11	61.1	6	33.3	18	100.0	5	100.0	23	100.0

In a secondary efficacy rating, 13 (72.2%) of the 18 episodes of PF treated with CEPROTIN were rated as excellent, 4 (22.2%) were rated as good, and 1 (5.6%) episode of severe PF was rated as fair; all were rated as effective. Four (80%) of the 5 episodes of venous thrombosis had treatment ratings of excellent, while 1 (20%) was rated as good.

CEPROTIN was also demonstrated to be effective in reducing the size and number of skin lesions. Non-necrotic skin lesions healed over a maximum 12-day (median 4-day) period and necrotic skin lesions healed over a maximum 52-day (median 11-day) period of CEPROTIN treatment, as shown in Table 6.

Table 6: Number of Days to Complete Healing of Skin Lesions in the Protein C Concentrate (Human) Pivotal Study

Lesion Type	Number of Episodes (Number of Subjects)	Mean	Median	Minimum	Maximum
Non-necrotic	16 (9 subjects)	4.6	4.0	1	12
Necrotic	7 (5 subjects)	21.1	11.0	5	52

Changes in the extent of venous thrombus were also measured for the 5 thromboembolic episodes. CEPROTIN prevented an increase in the extent of thrombus during 4 (80%) of the thromboembolic episodes by Day 3 of treatment, and 1 (20%) episode by Day 5 of treatment.

All seven of the short-term prophylaxis treatments with CEPROTIN were free of complications of PF or thromboembolic events, as shown in Table 7.

Table 7: Summary of Complications During Short Term Prophylaxis in the Protein C Concentrate (Human) Pivotal Study

Reason for Treatment	Number of Treatments	Presentation of Purpura Fulminans During Treatment Episodes		Thromboembolic Complications During Treatment Episode		Number of Treatments Free of Complications
		N	%	N	%	N	%
Anticoagulation Therapy	3	0	0.0	0	0.0	3	100.0
Surgical Procedure	4	0	0.0	0	0.0	4	100.0
Total	7	0	0.0	0	0.0	7	100.0

No episodes of PF occurred in four subjects ranging from 42 to 338 days of long-term prophylactic treatment with CEPROTIN, as shown in Table 8. When not on prophylactic treatment and receiving CEPROTIN on-demand, the same four subjects experienced a total of 13 (median of 3) episodes of PF over a range of 19 to 323 days. The time to first episode of PF after exiting from long-term prophylaxis treatment ranged from 12 to 32 days for these four subjects.

Table 8: Number and Rate of Episodes of Skin Lesions or Thrombosis for Four Subjects Who Received Long-Term Prophylactic Treatment and Were Treated On-Demand in the Protein C Concentrate (Human) Pivotal Study

Summary Statistic	Long-Term Prophylactic Treatment			While On-Demand 1			Time to First Episode After Existing Long Term Prophylaxis
	Number of Episodes per Subject	Number of Days Receiving Prophylactic Treatment	Monthly Rate of Episodes	Number of Episodes per Subject	Number of Days Not Receiving Study Drug	Monthly Rate of Episodes
Mean	0	229	0.0	3.3	165	1.91	23.3
Median	0	268	0.0	3.0	159	0.49	24.5
Minimum	0	42	0.0	1.0	19	0.25	12.0
Maximum	0	338	0.0	6.0	323	6.40	32.0