A Phase 3b, Open-Label, Single-Group Immunogenicity and Safety Study of Topical Recombinant Thrombin in Surgical Hemostasis

Thrombin and Thrombin-Incorporated Biomaterials for Disease Treatments

Thrombin, a coagulation-inducing protease, has long been used in the hemostatic field. During the past decades, many other therapeutic uses of thrombin have been developed. For instance, burn treatment, pseudoaneurysm therapy, wound management, and tumor vascular infarction (or tumor vasculature blockade therapy) can all utilize the unique and powerful function of thrombin. Based on their therapeutic effects, many thrombin-associated products have been certificated by the Food and Drug Administration, including bovine thrombin, human thrombin, recombinant thrombin, fibrin glue, etc. Besides, several thrombin-based drugs are currently undergoing clinical trials. In this article, the therapeutic uses of thrombin (from the initial hemostasis to the latest cancer therapy), the commercially available drugs associated with thrombin, and the pros and cons of thrombin-based therapeutics (e.g., adverse immune responses related to bovine thrombin, thromboinflammation, and vasculogenic "rebounds") are summarized. Further, the current challenges and possible future research directions of thrombin-incorporated biomaterials and therapies are discussed. It is hoped that this review may provide a valuable reference for researchers in this field and help them to design safer and more effective thrombin-based drugs for fighting against various intractable diseases.

Hemostatic Agents in Orthopedic Surgery

Controlling blood loss is a crucial aspect of orthopedic surgery. Hemostatic agents can be used intraoperatively in combination with antifibrinolytics as part of an overall strategy to limit blood loss. Several new hemostatic agents have recently come to the market designed specifically for vascular surgery but have found uses in other surgical fields, including orthopedics. This article reviews the mechanisms of action and best uses of various mechanical hemostats, active hemostats, flowable hemostats, and fibrin sealants for achieving hemostasis in orthopedic surgery. Mechanical and active hemostats have been reported to successfully decrease blood loss from cancellous bone, capillaries, and venules. Flowable hemostats are generally favorable for use in small spaces where the swelling capabilities of mechanical and active hemostats can be detrimental to surrounding structures. Sealants are best used for closing defects in tissues.

Blood utilization: fostering an effective hospital transfusion culture

An effective hospital transfusion culture should encourage clinicians to consider the possibility of transfusion in their patients well before the need actually arises, and to plan ahead in an attempt to use blood products most efficiently. Strategies for improved blood utilization include timely and adequate preoperative assessment of risk, optimization of baseline hemoglobin, anticipation of potential transfusion problems, intraoperative techniques to minimize blood loss, blood conservation technologies, transfusion guidelines and targeted therapy, point of care testing, and massive transfusion protocols. Attention to these elements promotes a safe and cost-effective transfusion culture.

Recombinant human thrombin: safety and immunogenicity in pediatric burn wound excision

BACKGROUND

Previous studies of recombinant human thrombin (rThrombin) enrolled adult and adolescent patients. This phase 4, open-label, single-group study was conducted in pediatric patients undergoing synchronous burn wound excision and skin grafting to provide information regarding the safety and immunogenicity of rThrombin (primary and secondary endpoints) in this population.

METHODS

Topical rThrombin was applied as a hemostatic aid during a surgical procedure (day 1). Adverse events and clinical laboratory abnormalities were recorded during the study. Immunogenicity samples were collected on days 1 and 29 (study end). Study results were summarized with descriptive statistics.

RESULTS

Thirty patients enrolled and 28 completed the study. Mean age was 6.9 years (range, 0.9-17.8 years); 40.0% of patients were girls. Flame and scald were the most common burn types (33.3% each, n = 10/30). Mean graft size was 3.6% total body surface area. Procedural pain (50.0% patients), pruritus (43.3%), and anemia (30.0%) were the most commonly reported adverse events. All adverse events and clinical laboratory abnormalities were considered unrelated to treatment. No patients developed anti-rThrombin product antibodies at day 29.

CONCLUSIONS

In pediatric patients undergoing burn wound excision and skin grafting, rThrombin was well tolerated and did not lead to the formation of anti-rThrombin product antibodies.

Iatrogenic cerebral venous sinus occlusion with flowable topical hemostatic matrix

Object

The use of commercially available topical hemostatic adjuncts has increased the safety profile of surgery as a whole. Cranial surgery has also benefited from the development of numerous agents designed to permit more rapid achievement of hemostasis. Flowable topical hemostatic agents applied via syringe injection are now commonly employed in many neurosurgical procedures, including cranial surgery. Intravascular use of these strongly thrombogenic agents is contraindicated, but in certain settings, inadvertent intravascular administration can occur, resulting in vascular occlusion, thrombosis, and potential dissemination. To date, there have no reports detailing the presence and incidence of this complication.

Methods

The authors conducted a retrospective review of all cranial surgeries performed at Presbyterian University Hospital by members of the University of Pittsburgh Medical Center's Department of Neurological Surgery between 2007 and 2009. Cases complicated by vascular occlusion due to inadvertent intravascular administration of flowable topical hemostatic matrix (FTHM) were identified and analyzed.

Results

Iatrogenic vascular occlusion induced by FTHM was identified in 5 (0.1%) of 3969 cranial surgery cases. None of these events occurred in 3318 supratentorial cases, whereas 5 cases of cerebral venous sinus occlusion occurred in 651 infratentorial cases (0.8%). The risk of accidental vessel occlusion was significantly associated with infratentorial surgery, and all events occurred in the transverse and/or sigmoid sinus. No episodes of inadvertent vascular occlusion occurred during endoscopic surgery. No cases of arterial occlusion were identified. Of the 5 patients with FTHM-related cerebral venous sinus occlusion, none developed long-term neurological sequelae referable to the event.

Conclusions

Inadvertent intravascular administration of FTHM is a rare complication associated with cranial surgery that occurs most commonly during infratentorial procedures around the transverse and/or sigmoid sinuses. Modifications in the choice of when to use an FTHM and the method of application may help prevent accidental venous sinus administration.

Adverse drug events associated with disorders of coagulation

Disorders of coagulation are common adverse drug events encountered in critically ill patients and present a serious concern for intensive care unit (ICU) clinicians. Dosing strategies for medications used in the ICU are typically developed for use in noncritically ill patients and, therefore, do not account for the altered pharmacokinetic and pharmacodynamic properties encountered in the critically ill as well as the increased potential for drug-drug interactions, given the far greater number of medications ordered. This substantially increases the risk for coagulation-related adverse reactions, such as a bleeding or prothrombotic events. Although many medications used in the ICU have the potential to cause coagulation disorders, the exact incidence will vary based on the specific medication, dose, concomitant drug therapy, ICU setting, and patient-specific comorbidities. Clinicians must strongly consider these factors when evaluating the risk/benefit ratio for a particular therapy. This review surveys recent literature documenting the risk for adverse drug reactions specific to bleeding and/or clotting with commonly used medications in the ICU.

Thrombin use in surgery: an evidence-based review of its clinical use

When surgical ligation of bleeding fails, or is not possible, surgeons rely on a number of hemostatic aids, including thrombin. This review discusses the history, pharmacology and clinical application of thrombin as a surgical hemostat. The initial thrombin was bovine in origin, but its use has been complicated by the formation of antibodies that cross-react with human coagulation factors. This has been associated with life-threatening bleeding and in some circumstances anaphylaxis and death. Human thrombin, isolated from pooled plasma of donors, was developed in an effort to minimize these risks, but its downsides are its limited availability and the potential for transmitting blood-borne pathogens. Recently a recombinant thrombin has been developed, and approved for use by the FDA. It has the advantage of being minimally antigenic and devoid of the risk of viral transmission. Thrombin is often used in conjunction with other hemostatic aids, including absorbable agents such as Gelfoam, and with fibrinogen in fibrin glues. The last part of this review will discuss these agents in detail, and review their clinical applications.

Cross-reactivity of rabbit anti-bovine thrombin IgGs with human alpha-thrombin and a recombinant version of human thrombin (Recothrom)

It has been reported that patients exposed to topical bovine thrombin preparations may develop antibodies against bovine thrombin, factr V or various other proteins found in these preparations. Such antibodies can cross-react with human endogenous coagulation proteins and may lead to alterations in the coagulation laboratory parameters, hypersensitivity reactions, and severe bleeding or thrombosis. The underlying mechanisms for the coagulopathy are not fully understood yet. To better understand the cross-reactivity of anti-bovine thrombin antibodies with human corresponding coagulation proteins, bovine crude thrombin, and its purified versions, thrombin 4A (the old version of Thrombin-JMI before year 2008) and thrombin 4B (the current version of Thrombin-JMI on market), were used to generate relevant anti-bovine thrombin immunoglobulin G (IgGs) in rabbits. Using Western blotting, the cross-reactivity of each IgG with human alpha-thrombin and a recombinant version of human thrombin (Recothrom) was investigated. The results indicated that no cross-reactivity with either human alpha-thrombin or Recothrom was observed with both anti-bovine crude thrombin IgGs and thrombin 4B IgGs. However, anti-bovine thrombin 4A IgGs showed apparent cross-reactivity with human alpha-thrombin and Recothrom in a protein amount-dependent manner. Furthermore, the results revealed that the cross-reactivity of anti-bovine thrombin 4A IgGs with human alpha-thrombin and Recothrom was immunization time-dependent. The minimum concentration of 4A IgG required to exhibit cross-reactivity with human alpha-thrombin and Recothrom varied considerably among individual rabbits. These results indicate that rabbit anti-bovine thrombin IgGs can cross-react with human alpha-thrombin and Recothrom, suggesting that human antibodies against bovine thrombin may also cross-react with human recombinant thrombin. Thus, the patients who were previously exposed to bovine thrombin may also develop antibodies which can cross-react with human recombinant thrombin.

Topical recombinant thrombin at a concentration of 1000 IU/mL reliably shortens in vivo TTH and delivers durable hemostasis in the presence of heparin anticoagulation and clopidogrel platelet inhibition in a rabbit model of vascular bleeding

Background

This study was designed to evaluate the effect of recombinant human thrombin (rThrombin) concentration on time to hemostasis (TTH), clot durability, and clot strength in settings that replicate the heparinization and platelet inhibition often found in surgical populations.

Methods

A modified, anticoagulated rabbit arteriovenous shunt preparation was selected to model vascular anastomotic bleeding. Rabbits were treated with heparin or heparin + clopidogrel and TTH was measured after applying a range of topical rThrombin concentrations or placebo, in combination with absorbable gelatin sponge, USP. Treatments (placebo, rThrombin) were randomly assigned and the investigator was blinded to treatment. TTH was evaluated with the Kaplan-Meier method. After hemostasis was achieved, clot burst assessment was performed for heparin + clopidogrel treated animals. Clot viscoelastic strength and kinetics were measured in ex-vivo samples using thromboelastography (TEG) methods.

Results

TTH decreased with increasing concentrations of rThrombin in heparin-treated animals and was shorter after treatment with 1000 IU/mL rThrombin (73 seconds) than with 125 IU/mL rThrombin (78 seconds; p = 0.007). TTH also decreased with increasing concentrations of rThrombin in heparin + clopidogrel treated animals; again it was significantly shorter after treatment with 1000 IU/mL rThrombin (71 seconds) than with 125 IU/mL rThrombin (177 seconds; p < 0.001). Variability in TTH was significantly smaller after treatment with 1000 IU/mL rThrombin than after 125 IU/mL rThrombin, indicating greater reliability of clot formation (p < 0.001 for heparin or heparin + clopidogrel treatments). Clot durability was examined in heparin + clopidogrel treated animals. Clots formed in the presence of 1000 IU/mL rThrombin were significantly less likely to rupture during clot burst assessment than those formed in the presence of 125 IU/mL rThrombin (0% versus 79%, p < 0.001). In vitro clot strength and clot kinetics, as determined by TEG in heparin + clopidogrel samples, were positively associated with the amount of rThrombin activity added for clot initiation.

Conclusion

In an animal model designed to replicate the anti-coagulation regimens encountered in clinical settings, topical rThrombin at 1000 IU/mL more reliably controlled the pharmacological effects of heparin or heparin + clopidogrel on hemostasis than rThrombin at 125 IU/mL. Results from in vitro assessments confirmed a positive relationship between the amount of rThrombin activity and both the rate of clot formation and clot strength.

Safety of topical thrombins: the ongoing debate

Until recently, only bovine-derived thrombin was available for use as a stand-alone topical hemostat or as a component of other hemostatic devices. Concerns over a number of case reports of immune-mediated coagulopathies associated with the use of bovine-derived thrombin resulted in a United States Food and Drug Administration warning letter being issued in 1996 and the later addition of a boxed warning ("Black Box Warning") to all bovine-derived thrombin products. Since 2007, both a human-pooled plasma thrombin product and a recombinant thrombin have entered the market.

With the addition of these two products to the topical thrombin class, a unique situation has developed in which only a single member (bovine-derived thrombin) within the class carries the Food and Drug Administration's strongest cautionary language about possible adverse events related to an agent's use. Neither the human-pooled plasma thrombin nor the recombinant thrombin products have a boxed warning; although, the human-pooled plasma product does include a precaution/warning about infectious agent transmission - a warning common to products derived from human sources. This report will address this unique situation and the impact, clinical and non-clinical, that thrombin choice may have. Since alternatives are now available, institutions may need to revisit their formulary choice of thrombin preparation, taking into consideration the potential risks associated with bovine-derived products.