Antifibrinolytic treatment in haemophilia: a controlled trial of prophylaxis with tranexamic acid

Fibrin(ogen) as a Therapeutic Target: Opportunities and Challenges

Fibrinogen is one of the key molecular players in haemostasis. Thrombin-mediated release of fibrinopeptides from fibrinogen converts this soluble protein into a network of fibrin fibres that form a building block for blood clots. Thrombin-activated factor XIII further crosslinks the fibrin fibres and incorporates antifibrinolytic proteins into the network, thus stabilising the clot. The conversion of fibrinogen to fibrin also exposes binding sites for fibrinolytic proteins to limit clot formation and avoid unwanted extension of the fibrin fibres. Altered clot structure and/or incorporation of antifibrinolytic proteins into fibrin networks disturbs the delicate equilibrium between clot formation and lysis, resulting in either unstable clots (predisposing to bleeding events) or persistent clots that are resistant to lysis (increasing risk of thrombosis). In this review, we discuss the factors responsible for alterations in fibrin(ogen) that can modulate clot stability, in turn predisposing to abnormal haemostasis. We also explore the mechanistic pathways that may allow the use of fibrinogen as a potential therapeutic target to treat vascular thrombosis or bleeding disorders. Better understanding of fibrinogen function will help to devise future effective and safe therapies to modulate thrombosis and bleeding risk, while maintaining the fine balance between clot formation and lysis.

Antifibrinolytic therapy for preventing oral bleeding in patients with haemophilia or Von Willebrand disease undergoing minor oral surgery or dental extractions

BACKGROUND

Minor oral surgery or dental extractions (oral or dental procedures) are widely performed and can be complicated by hazardous oral bleeding, especially in people with an inherited bleeding disorder such as haemophilia or Von Willebrand disease (VWD). The amount and severity of singular bleedings depend on disease-related factors, such as the severity of the haemophilia, both local and systemic patient factors (such as periodontal inflammation, vasculopathy or platelet dysfunction) and intervention-related factors (such as the type and number of teeth extracted or the dimension of the wound surface). Similar to local haemostatic measures and suturing, antifibrinolytic therapy is a cheap, safe and potentially effective treatment to prevent bleeding complications in individuals with bleeding disorders undergoing oral or dental procedures. However, a systematic review of trials reporting outcomes after oral surgery or a dental procedure in people with an inherited bleeding disorder, with or without, the use of antifibrinolytic agents has not been performed to date. This is an update of a previously published Cochrane Review.

OBJECTIVES

Primarily, we aim to assess the efficacy of antifibrinolytic agents to prevent bleeding complications in people with haemophilia or VWD undergoing oral or dental procedures.Secondary objectives are to assess if antifibrinolytic agents can replace or reduce the need for clotting factor concentrate therapy in people with haemophilia or VWD and to establish the effects of these agents on bleeding in oral or dental procedures for each of these patient populations.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Coagulopathies Trials Register, compiled from electronic database searches of the Cochrane Central Register of Controlled Trials (CENTRAL), of MEDLINE and from handsearching of journals and conference abstract books. We additionally searched the reference lists of relevant articles and reviews. We searched PubMed, Embase, Cinahl and the Cochrane Library. Additional searches were performed in ClinicalTrials.gov, WHO International Clinical Trials Registry Platform (ICTRP).Date of last search of the Cystic Fibrosis and Genetic Disorders Group's Coagulopathies Trials Register: 01 March 2019.

SELECTION CRITERIA

Randomised and quasi-randomised controlled trials in people with haemophilia or VWD undergoing oral or dental procedures using antifibrinolytic agents (tranexamic acid or epsilon aminocaproic acid (EACA)) to prevent perioperative bleeding compared to no intervention or usual care with or without placebo.

DATA COLLECTION AND ANALYSIS

Two authors independently screened the titles and abstracts of all identified articles. Full texts were obtained for potentially relevant abstracts and two authors independently assessed these for inclusion based on the selection criteria. A third author verified trial eligibility. Two authors independently performed data extraction and risk of bias assessments using standardised forms.

MAIN RESULTS

While there were no eligible trials in people with VWD identified, two randomised, double-blind, placebo-controlled trials (total of 59 participants) in people with haemophilia undergoing dental extraction were included. One trial of tranexamic acid published in 1972 included 28 participants with mild, moderate or severe haemophilia A and B and one of EACA published in 1971 included 31 people with haemophilia with factor VIII or factor IX levels less than 15%. Overall, the two included trials showed a beneficial effect of tranexamic acid and EACA, administered systemically, in reducing the number of bleedings, the amount of blood loss and the need for therapeutic clotting factor concentrates. Regarding postoperative bleeding, the tranexamic acid trial showed a risk difference (RD) of -0.64 (95% confidence interval (CI) -0.93 to - 0.36) and the EACA trial a RD of -0.50 (95% CI 0.77 to -0.22). The combined RD of both trials was -0.57 (95% CI -0.76 to -0.37), with the quality of the evidence (GRADE) for this outcome is rated as moderate. Side effects occurred once and required stopping EACA (combined RD of -0.03 (95% CI -0.08 to 0.13). There was heterogeneity between the two trials regarding the proportion of people with severe haemophilia included, the concomitant standard therapy and fibrinolytic agent treatment regimens used. We cannot exclude that a selection bias has occurred in the EACA trial, but overall the risk of bias appeared to be low for both trials.

AUTHORS' CONCLUSIONS

Despite the discovery of a beneficial effect of systemically administered tranexamic acid and EACA in preventing postoperative bleeding in people with haemophilia undergoing dental extraction, the limited number of randomised controlled trials identified, in combination with the small sample sizes and heterogeneity regarding standard therapy and treatment regimens between the two trials, do not allow us to conclude definite efficacy of antifibrinolytic therapy in oral or dental procedures in people with haemophilia. No trials were identified in people with VWD.

Antifibrinolytic therapy for preventing oral bleeding in patients with haemophilia or Von Willebrand disease undergoing minor oral surgery or dental extractions

BACKGROUND

Minor oral surgery or dental extractions (oral or dental procedures) are widely performed and can be complicated by hazardous oral bleeding, especially in people with an inherited bleeding disorder such as haemophilia or Von Willebrand disease. The amount and severity of singular bleedings depend on disease-related factors, such as the severity of the haemophilia, both local and systemic patient factors (such as periodontal inflammation, vasculopathy or platelet dysfunction) and intervention-related factors (such as the type and number of teeth extracted or the dimension of the wound surface). Similar to local haemostatic measures and suturing, antifibrinolytic therapy is a cheap, safe and potentially effective treatment to prevent bleeding complications in individuals with bleeding disorders undergoing oral or dental procedures. However, a systematic review of trials reporting outcomes after oral surgery or a dental procedure in people with an inherited bleeding disorder, with or without, the use of antifibrinolytic agents has not been performed to date.

OBJECTIVES

The primary objective was to assess the efficacy of local or systemic use of antifibrinolytic agents to prevent bleeding complications in people with haemophilia or Von Willebrand disease undergoing oral or dental procedures. Secondary objectives were to assess if antifibrinolytic agents can replace or reduce the need for clotting factor concentrate therapy in people with haemophilia or Von Willebrand disease and to further establish the effects of these agents on bleeding in oral or dental procedures for each of these populations.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Coagulopathies Trials Register, compiled from electronic database searches of the Cochrane Central Register of Controlled Trials (CENTRAL), of MEDLINE and from handsearching of journals and conference abstract books. We additionally searched the reference lists of relevant articles and reviews. We searched PubMed, Embase and The Cochrane Library. Additional searches were performed in ClinicalTrials.gov, WHO International Clinical Trials Registry Platform (ICTRP).Date of last search of the Cystic Fibrosis and Genetic Disorders Group's Coagulopathies Trials Register: 14 December 2015.

SELECTION CRITERIA

Randomised and quasi-randomised controlled trials in people with haemophilia or Von Willebrand disease undergoing oral or dental procedures using antifibrinolytic agents (tranexamic acid or epsilon aminocaproic acid) to prevent perioperative bleeding compared to no intervention or usual care with or without placebo.

DATA COLLECTION AND ANALYSIS

Two authors independently screened the titles and abstracts of all identified articles. Full texts were obtained for potentially relevant abstracts and two authors independently assessed these for inclusion based on the selection criteria. A third author verified trial eligibility. Two authors independently performed data extraction and risk of bias assessments using standardized forms.

MAIN RESULTS

While there were no eligible trials in people with Von Willebrand disease identified, two randomised, double-blind, placebo-controlled trials (total of 59 participants) in people with haemophilia undergoing dental extraction were included. One trial of tranexamic acid published in 1972 included 28 participants with mild, moderate or severe haemophilia A and B and one of epsilon aminocaproic acid published in 1971 included 31 people with haemophilia with factor VIII or factor IX levels less than 15%. Overall, the two included trials showed a beneficial effect of tranexamic acid and EACA, administered systemically, in reducing the number of bleedings, the amount of blood loss and the need for therapeutic clotting factor concentrates. Regarding postoperative bleeding, the tranexamic acid trial showed a risk difference of -0.64 (95% confidence interval -0.93 to - 0.36) and the EACA trial a risk difference of -0.50 (95% confidence interval 0.77 to -0.22). The combined risk difference of both trials was -0.57 (95% confidence interval -0.76 to -0.37), with the quality of the evidence (GRADE) for this outcome is rated as moderate. Side effects occurred once and required stopping epsilon aminocaproic acid (combined risk difference of -0.03 (95% CI -0.08 to 0.13). There was heterogeneity between the two trials regarding the proportion of people with severe haemophilia included, the concomitant standard therapy and fibrinolytic agent treatment regimens used. We cannot exclude that a selection bias has occurred in the epsilon aminocaproic acid trial, but overall the risk of bias appeared to be low for both trials.

AUTHORS' CONCLUSIONS

Despite the discovery of a beneficial effect of systemically administered tranexamic acid and epsilon aminocaproic acid in preventing postoperative bleeding in people with haemophilia undergoing dental extraction, the limited number of randomised controlled trials identified, in combination with the small sample sizes and heterogeneity regarding standard therapy and treatment regimens between the two trials, do not allow us to conclude definite efficacy of antifibrinolytic therapy in oral or dental procedures in people with haemophilia. No trials were identified in people with Von Willebrand disease.

Tranexamic acid combined with recombinant factor VIII increases clot resistance to accelerated fibrinolysis in severe hemophilia A

BACKGROUND

Most patients with severe hemophilia A suffer from a profoundly compromised hemostatic response. In addition to both the delayed and slow development of a clot, previous studies have documented that severe hemophilia A is also associated with reduced clot stability.

OBJECTIVES

We examined whether the clot stability in hemophiliacs could be improved by treatment with tranexamic acid (TXA) in combination with recombinant factor VIII (rFVIII).

PATIENTS/METHODS

Baseline blood samples were obtained from eight males with severe hemophilia A. Thereafter, a bolus injection of rFVIII was administered to increase the functional level of FVIII to approximately 50%. After 10 min, blood was collected followed by an intravenous injection of TXA. A third blood sample was obtained after a further 10 min. Whole blood clotting profiles were determined by thrombelastography using minimal tissue factor activation. Clot formation was assessed by both clot initiation and clot propagation. At clot termination, the maximum clot firmness and area under the elasticity curve were used to illustrate clot stability. Tissue-plasminogen activator was included in those experiments designed to assess clot stability.

RESULTS

As expected, rFVIII increased clot formation, whereas TXA had no effect upon this parameter. Assays including tissue-plasminogen activator revealed that rFVIII increased the maximum clot firmness 3-fold; whereas the presence of TXA induced an additional 4-fold increase. The area under the elasticity curve increased 5-fold after rFVIII and 24-fold after addition of TXA.

CONCLUSIONS

The study demonstrates that simultaneous treatment with TXA and rFVIII significantly improves the clot stability in patients with hemophilia A.

The fibrinolytic system in man

The existence of a system in the human body capable of inducing the dissolution of endogenous pathologically formed thrombi was appreciated in ancient times. Considered in detail in this article are the data that have elucidated the physiologic regulation of which plasmin formation is dependent on, the plasma concentration of plasminogen, availability of activators of plasminogen in the plasma and surrounding tissue environment, the concentration of naturally present inhibitors, and the existence of fibrin in the circulation. Important in this rapidly progressive scientific discipline is consideration of the factors which control the synthesis of the components of this proteolytic enzyme system. Recently abundant information has indicated that this plasminogen-plasmin proteolytic enzyme system can be utilized therapeutically. Knowledge of the mechanisms of this system has permitted identification of agents that can be exogenously administered to releave thrombotic obstruction to blood flow in the venous (pulmonary emboli, deep vein thrombosis) and arterial (peripheral and central vessels) circulatory systems. Particularly important is the demonstration that thrombolytic agents can directly attack and alleviate the immediate cause of acute myocardial infarction. As a result of the innovations in the present decade, it is evident that the plasminogen system can be advantageously employed to reverse the pathologic effects of all thrombotic diseases.