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Pharmacology / Toxicology Review Memorandum - ARTISS

M E M O R A N D U M

Department of Health and Human Services
Food and Drug Administration
Center for Biologics Evaluation and Research

Pharmacology / Toxicology Review Memorandum

Date: February 26, 2008 (Final review memo)
From: Paul W. Buehler
Through: Abdu Alayash, Susan Abbondanzo and Basil Golding
To: Pratibha Rana and Tim Lee
Subject: STN-125266 Fibrin Sealant (FS VH S/D 4, frozen and lyophilized) for adhering autologous skin grafts to surgically prepared wound beds resulting from burns in adults and pediatric populations.
Sponsor: Baxter Healthcare
Receipt Date: June 1, 2007
Middle Cycle/Final Review: November 1, 2007

Recommendation:

STN 125266-0 is approvable from a pharmacology and toxicology perspective.

Primary toxicology was carried out in submission # STN 103980/5224 which supported approval of TISSEEL VH S/D with synthetic aprotinin at thrombin concentrations 125x the concentration present in the FS VH S/D 4 product. Otherwise the TISSEEL VH S/D and FS VH S/D 4 are no different in terms of chemical composition. It is not believed that reduction in thrombin present in the FS VH S/D 4 product would lead to toxicology not associated with TISSEEL VH S/D (see appendix for studies and review of studies submitted with STN 103980/5224).

Indication:

Fibrin Sealant, VH S/D 4 (frozen and lyophilized) is indicated to adhere to autologous skin grafts and surgically prepared wound beds resulting from burns in adult and pediatric populations. The product is supplied as a lyophilized powder to be reconstituted as 2 mL (100 cm2), 4mL (200 cm2) and 10 mL (500 cm2) volumes, depending on surface area to be covered.

Background:

On 27 July 2006, FDA approved eBLA supplement (STN: BL 103980/5121) supporting licensure of Baxter's next generation Fibrin Sealant, "TISSEEL VH S/D". Fibrin Sealant, Vapor Heated, Solvent/Detergent Treated (TISSEEL VH S/D) is a further development of TISSEEL VH Fibrin Sealant. Viral inactivation steps are included in the manufacturing process of both TISSEEL VH Fibrin Sealant and TISSEEL VH S/D to address the potential for transmission of viral pathogens. Solvent/detergent treatment of both biological components of TISSEEL VH S/D, specifically Sealer Protein Concentrate (Human) and Thrombin (Human) provides an increased margin of safety relative to TISSEEL VH Fibrin Sealant. On 26 February 2007, FDA approved the PAS (STN: BL 103980/5224) supporting replacement of the bovine aprotinin with equivalent synthetically derived aprotinin supplied by --------- (see appendix).

Fibrin Sealant VH S/D 4 is a parallel development to TISSEEL Fibrin Sealant (BL 103980). Except for the difference in thrombin concentration (4 IU/ml vs. 500 IU/ml), the manufacturing process for Fibrin Sealant VH S/D 4 -----------------------. The process includes stringent plasma collection and screening processes, as well as two distinct viral inactivation steps that are included in the manufacturing process of both biological components to address the potential for transmission of viral pathogens, heat treatment and solvent/detergent treatment. The concentration of thrombin directly influences coagulation properties. Rapid hemostasis and sealing can be achieved with high amounts of thrombin (TISSEEL) resulting in virtually immediate clot formation. For this reason, thrombin concentrations of 500 IU/ml are usually used for surgical procedures were hemostasis and sealing have to be as fast as possible. However, in situations when time for additional handling is needed after applying the sealant, low thrombin concentrations (e.g 4 IU/ml) are of considerable advantage. Due to the prolonged clotting time, sealants containing low amounts of thrombin are used as biological tissue glues for procedures such as skin grafting. The present file contains one primary non-clinical study evaluating both efficacy and toxicity of Fibrin Sealant VH S/D 4 in a pig model of skin grafting.

The compositions of the two biologic components of FS VH S/D 4 (frozen and lyophilized) and TISSEEL VH S/D, are summarized below:

[         ]

Non-clinical studies:

PV 0270102 Sealing of autologous skin grafts in a pig model

Objective: to evaluate/compare wound repair with Fibrin Sealant VH S/D 4 at two different dosages with conventional sutures or spray fibrin sealant (TISSEEL VH) in pigs with a full thickness skin grafts.

Methods: 24 test sites were randomly distributed among 6 animals at 4 site locations on the backs of animals as follows in the diagram below:

 

view of test sites

 

Four full skin thickness defects (4x8 cm), the defects were covered with autologous split skin grafts using fibrin sealant or sutures.

flowchart showing which group of animals received autologous split skin grafts using fibrin sealant or sutures

 

Primary end points:

  • Seroma and hematoma formation at 7 days
  • Take rate at 7 and 14 days
  • Assessment of wound area healed at 21 days

Secondary endpoints:

  • Ease of application and time for grafting
  • Local tolerance histopathology

Scoring/statistics: For comparisons between groups the primary end-points were combined into a rank sum score per site. For this purpose all variables were ranked over treatment groups. For seroma and hematoma formation at 7, 14 and 21 days, lower values received higher ranks. The rank was added up over all variables and the means. A higher rank sum score indicates a better performance.

Results

Differences in primary endpoints:

 

Table showing differences in primary endpoints

Differences in secondary endpoints:

differences in secondary endpoints

 

Healed wound area at 21 days:

Table showing information on healed wound area at 21 days

 

Local tolerance histological findings:

There were no differences between groups in terms of local histology findings at 14 days with most groups demonstrating no (score =0) or low (score=1) for foreign body reaction and residual fibrin. Inflammation was higher across groups with typical scoring of medium (score=2).

Conclusion:

The present study suggests that a fibrin sealant at low concentrations can improve split skin graft fixation compared to standard suturing techniques. No differences between higher and lower dose thrombin were detected in terms of efficacy or local histopathology.

Appendix (STN-103980/5224)

Overview of the Non-clinical Testing Strategy:

Study report (ARC-UL-0791) - "Synthetic Aprotinin": Salmonella Typhimurium reverse mutation test

Study report (PV0890301) - Pharmacokinetics of synthetic aprotinin after intravenous administration in mice

Study report (0910301) - Synthetic aprotinin: Bronchospastic activity in guinea pigs

Study report (1150302) - A comparative evaluation of the sustained hemostatic effacacies of TISSEEL VH S/D s-apr DUO 500 versus TISSEEL VH S/D DUO 500 in a Rabbit liver resection model with acute hyperfibrinolysis

Study report (PV0920301) - Determination of acute toxicity in mice after intravenous administration of synthetic aprotinin

Study report (PV1240402) - Evaluation of the acute toxicity of tisseel VH S/D s-apr Duo 500 versus TISSEEL VH S/D DUO 500 in a rat model

Study report (PV0960301) - Investigation of local tolerance of synthetic aprotinin in rabbits

Study report (PV1280402) - A comparative evaluation of the local tissue reaction of TISSEEL VH S/D s-apr DUO 500 versus TISSEEL VH S/D Duo 500 in a wound healing model (rat)

Study report (PV0940301) - Synthetic aprotinin: skin sensitization study

Pharmacology (efficacy):

Study report (1150302) - A comparative evaluation of the sustained hemostatic effacacies of TISSEEL VH S/D s-apr DUO 500 versus TISSEEL VH S/D DUO 500 in a Rabbit liver resection model with acute hyperfibrinolysis
s-apr = synthetic aprotinin, bv-apr = bovine aprotinin

Summary:

Study 1150302 represents the pivotal "efficacy" study in the evaluation of s-apr in vivo potency comparability to bv-apr in accordance with 21 CFR § 600.3 (potency definition).

Materials evaluated

Test Item - (TISSEEL VH S/D s-apr DUO 500)

[         ]

Reference Item - (TISSEEL VH S/D DUO 500)

[         ]

Model Rationale/Relevance:

The liver resection model in the rabbit is a reasonable and appropriate model of bleeding for the evaluation of s-apr versus bv-apr for the following reasons: (1) the model represents the type of bleeding for which TISSEEL VH is indicated (i.e. microvascular non-arterial bleeding) and (2) the liver has low intrinsic fibrinolytic potential thus reducing variability.

Study Design:

Under anesthesia (Ketamine/Xylazine maintained with thiopental) 24 animals were heparinized with 4.000 IU/kg. The left liver lobe was resected and control of bleeding was attempted by either test or reference material using a DUPOLJECT applicator (clinically intended method of application). Animals were randomized after liver resection and investigators were blinded to test or reference material.

Flow chart separating group a and group b of 24 randomized rabbits

 

Twenty minutes after liver resection streptokinase was administered as a bolus injection of 20,000 IU followed by continuous infusion of 40,000 IU over one hour. Blood loss at the sealed surface was quantified for two hours after sealing.

The primary end points were:

1) Blood loss (g) over the first hour after streptokinase administration
2) Blood loss (g) over the second hour after streptokinase administration
3) Total blood loss (g) over the first and second hour after streptokinase administration

Statistical analysis was summarized by median values, 95% confidence intervals of the medians and quartiles (Q1 = 25th, Q2 =50th and Q3 = 75th percentiles) for study arms A and B.

Results:

There was a slight non-significant increase (P>0.05) in blood loss over the first hour and for the combined 2 hour bleeding time evaluations with s-apr versus bv-apr.

Table showing amount of blood loss over one hour, 2 hours, and total s-apr versus bv-apr

 

Blood loss per animal over the initial hour, second hour and total time of evaluation

Table showing amount of blood loss over one hour, 2 hours, and total

 

Conclusion:

Based on the Baxter's and this reviewers statistical analysis no statistically significant differences occurred in bleeding time when comparing s-apr versus bv-apr in the rabbit liver resection model of bleeding. The slight trend toward increased bleeding in thes-apr treated group is approximately 0.37 (g) across animals over the initial hour and approximately 0.42 (g) across animals over the total time of evaluation. These differences are unlikely to show a clinically different response to s-apr versus bv-apr in TISSEEL VH.

Pharmacokinetics/Toxicokinetics:

Study report (PV0890301) - Pharmacokinetics of synthetic aprotinin after intravenous administration in mice

Summary: The study was performed to test and compare the pharmacokinetic (PK) handling of s-apr versus bv-apr following single i.v. dosing. Based on AUC, total body clearance, MRTi..v. and t1/2 there appears to be no differences in the overall PK of s-apr versus bv-apr in the mouse.

Material evaluated

[         ]

Model Rationale/Relevance:

No rationale is provided for use of the mouse as a human PK relevant species. Nonetheless the mouse is adequate based on the idea of comparative PK for "equivalent" products (s-apr versus bv-apr).

Study design:

Six animals per group/time point were randomized to receive (A) s-apr (lot1), (B) s-apr (lot2), (C) bv-apr (lot1) or (D) bv-apr (lot2). All animals were dose with 500,000 KIU/kg (in 20 mL/kg). At 0, 5, 15, 60, 120 minutes and 6 hours post i.v administration 6 animals per group/time point were exsanguinated by cardiac puncture. Serum sample were evaluated by an ----------- method for the determination of aprotinin.

Results:

Actual Doses (ug/kg) Received:

 

Table showing doses received per test item

 

Overall PK Parameters:

Table showing overall PK parameters

 

PK Parameters per Lot:

Table showing PK parameters per lot

Conclusion:

The PK study would likely have provided much more reliable comparative data if performed following serial blood collections in the same animal after dosing (n=5 per group). The present study introduces a large degree of variability.

Toxicology Overview:

Single Dose Toxicity:

Study report (PV0920301) - Determination of acute toxicity in mice after intravenous administration of synthetic aprotinin

Summary:

No deaths occurred in any dosing group, clinical sign and symptoms were generally absent and gross pathological findings were insignificant.

Study Design:

Test animals were divided into sixteen groups each with ten animals (5M, 5F) according to the following treatment scheme.

Table showing treatment scheme

Table showing treatment scheme

 

Each animal received a single intravenous injection of the assigned test or reference material into the caudal vein at a flow rate of ≤ 2 mL/min. On day 14 all mice were humanely killed with CO2. The primary endpoint of this study was mortality. Thus only gross necropsy was performed at day 14 with tissue being preserved for histopathology if gross lesions were observed.

Results:

Clinical Symptoms:

No significant findings, other than behavioral depression in all treatment groups with a NOAEL of 100,000 KIU/kg i.v. in mice.

Body masses at low, medium and high doses:

Body masses at medium and high doses of s-apr demonstrated slightly greater weight gain over bv-apr treated animals.

Gross Pathology and Histopathology:

No significant findings

Table VII: Ratio of pathological findings and corresponding 95% confidence intervals for the synthetic aprotinin and the bovine aprotinin

 

Conclusion: No difference in s-apr versus bv-apr in terms of gross toxicity in mice.

Study report (PV1240402) - Evaluation of the acute toxicity of tisseel VH S/D s-apr Duo 500 versus TISSEEL VH S/D DUO 500 in a rat model

Summary:

No deaths occurred in any dosing group, clinical sign and symptoms were generally absent and gross pathological findings were insignificant. This study was designed to evaluate acute toxicity response to the complete TISSEEL product with either s-apr or bv-apr.

Study Design:

24 rats were randomized to receive the components of TISSEEL with s-apr or bv-apr as follows:

chart separating group a and group b with s-apr or bv-apr

 

Application/administration of TISSEEL was via the subcutaneous route, this is a technique that has been used successfully in previous animal toxicity studies of in vivo sealant material. Dosing was based on 5 mL/kg of body weight, thus approximating 10x the normal human application. A 40 mL application in an 80 kg individual equals 400 mL or 5 mL/kg bodyweight.

Results:

Body Weights:

Table showing body weight information

 

Gross Pathology and Histopathology:

No significant gross pathology or histopathology was observed

Repeat-Dose Toxicity:

Not performed

Genotoxicity:

Study report (ARC-UL-0791) - "Synthetic Aprotinin": Salmonella Typhimurium reverse mutation test

This is the standard Ames test used to evaluate genetic material alteration required by OECD guidelines. The overall findings indicate that in five strains of bacteria no genetic alterations occurred at the maximum concentration of s-apr or bv-apr that could be applied.

Carcinogenicity:

Not performed

Immunogenicity:

Study report (0910301) - Synthetic aprotinin: Bronchospastic activity in guinea pigs

Summary: The study was performed to test anaphylactoid response to s-apr in a highly sensitive model of acute bronchocspasm. There were no positive anaphylactoid reactions to either s-apr or bv-apr in the guinea pig after rapid i.a. administration.

Material evaluated

[         ]

Model Rationale/Relevance:

The anaphylactoid response in guinea pigs lends itself to critical evaluation of intra-arterial administered induction of histamine with increases in pulmonary filtration pressure. Thus the objective of the study was to study bronchospastic activity of s-apr versus bv-apr under rapid intra-arterial administration.

Study design:

Guinea pigs (n=6/group) were randomized to receive 20,000 KIU/kg s-apr, bv-apr or buffer administered through a carotid catheter. The measured end point was pulmonary infiltration pressure.

Results:

Table 1: Proportion of animals with positive reactions and 95% confidence intervals for the treatment phase

 

Conclusions:

No anaphylactoid or bronchospastic reactions were observed in s-apr, bv-apr or buffer control animals. Thus s-apr does not appear to be any more likely to generate anaphylaxsis in the guinea pig when compared to bv-apr.

Reproductive Studies:

Not performed

Local Tolerance Testing:

Study report (PV0960301) - Investigation of local tolerance of synthetic aprotinin in rabbits

Study report (PV1280402) - A comparative evaluation of the local tissue reaction of TISSEEL VH S/D s-apr DUO 500 versus TISSEEL VH S/D Duo 500 in a wound healing model (rat)

Study report (PV0940301) - Synthetic aprotinin: skin sensitization study

Conclusions from the local tolerance tests suggest no increased risk of local irritation or pathology due to addition of s-apr versus bv-apr.

Reviewer Recommendation:

The present submission demonstrates the following in accordance with 21 CFR § 600.3 under (p) safety and (s) potency.

(1) The synthetic form of aprotinin (s-apr) is equally safe compared to bovine source aprotinin (bv-apr) based on non-clinical GLP toxicology evaluation comparing the two head to head.

(2) The synthetic form of aprotinin (s-apr) is equally potent compared to bovine source aprotinin (bv-apr) in vivo based on non-clinical GLP comparability studies, which reflect the intended use of the product component.

From a non-clinical Pharmacology-Toxicology perspective the synthetic form of aprotinin is equivalent to bovive source aprotinin and is approvable for use in the TISSEEL end product.