J Clin Pathol: first published as 10.1136/jcp.33.Suppl_14.35 on 1 January 1980. Downloaded from

J Clin Pathol .33, Suppl (P oy Coll Path), 14, 35-40

Therapeutic considerations Basis of antifibrinolytic therapy

CRM PRENTICE From the University Department ofMedicine, Royal Infirmary, Glasgow

The and fibrinolytic enzyme systems the antifibrinolytic and then consider the oppose each other in the haemostatic process. clinical situations in which they might be expected to Coagulation occurs, of necessity, rapidly and be beneficial. Others will discuss the explosively so that a site of vessel damage causing and detailed clinical indications for the . loss can be rapidly sealed. The fibrinolytic process, on the other hand, serves as a repair system Mode of action of fibrinolytic inhibitors to remove fibrin deposits which might otherwise cause permanent vascular occlusion. This must The main inhibitors in current use comprise epsilon- occur slowly so that vascular repair and re-endothe- , , and . lialisation can take place before the fibrin is removed. The chemical formulae for these compounds are Therefore there is an elaborate system of inhibitors shown in the Figure. of plasminogen activator and in the cir- culation to prevent hyperplasminaemia and the E- aminocaproic acid indiscriminate digestion of . Additionally, copyright. is determined by the binding and spatial relationship between fibrin, Lys-plasminogen, H H H H H and activator. In this way selective fibrin digestion H2N- C - C - C - C - C- COOH can occur without systemic proteolytic activity. The structure of fibrin is also important in determining H H H H H the rate of . In cross-linked fibrin the normally susceptible alpha-chain has become A M C A - tranexamic acid polymerised to alpha-polymer, which is inaccessible http://jcp.bmj.com/ and resistant to plasmin action.' In this situation and the the beta-chain is digested first polymerised trans- 4 - aminomethylcyclohexane carboxylic acid. fibrin is much more robust than the non-crosslinked material.2 There are two major situations where the healthy physiological balance between coagulation and H 2N- CH2 COOH fibrinolysis may be lost, leading to a need for antifibrinolytic therapy. Firstly, unopposed fibrino- on September 29, 2021 by guest. Protected lytic activity may be excessive so that forming or APROTININ formed fibrin is digested by plasmin before a firm haemostatic plug is produced. Secondly, in the presence of a coagulation defect such as haemophilia the fibrin may be so inadequate in amount that physiological fibrinolytic activity may be sufficient to start haemorrhage. Several causes, however, may operate together to cause haemorrhage. For instance, in the presence of defective small vessel constriction or low-grade disseminated intravascular coagulation the action of the normal fibrinolytic response may be sufficient to initiate haemorrhage. Fig. Chemical formulae of E-aminocaproic acid, In this review I outline the mechanism of action of tranexamic acid, and aprotinin. 35 J Clin Pathol: first published as 10.1136/jcp.33.Suppl_14.35 on 1 January 1980. Downloaded from

36 Prentice

EPSILON-AMINOCAPROIC ACID (EACA, is reduced. This potent action of aminocaproic acid 6-AMINOHEXANOIC ACID) as an inhibitor ofplasmin in physiological fibrinolysis The approved name, British Pharmacopeia, of this on a substrate of fibrinogen or fibrin has been compound is aminocaproic acid. It was introduced recognised only fairly recently since much of the by Okamoto and colleagues.3 The relation between earlier work was carried out using casein as a its chemical structure and its antifibrinolytic substrate for plasmin.8 10 Similarly, aminocaproic activity is well established, based on its action as a acid is relatively inactive against the hydrolytic lysine substitute. The 5 carbon chain is important action of plasmin on synthetic esters. Thus the for its optimum action. Molecules with a longer striking action of aminocaproic acid is to block the or shorter aliphatic chain have lesser activity. action of plasmin on fibrin. Similarly, the amino- and carboxylic-acid radicles The interaction between plasminogen, plasmin, are both important for inhibitory activity.4 activator, and fibrin is complex.9 Tissue activators adsorb on to fibrin" and in the presence of plasmin- CYCLIC AMINOCARBOXYLIC ACIDS ogen mediate proteolytic cleavage of the terminal (TRANEXAMIC ACID, BP) part of plasminogen, changing 'native' Glu-plas- A series of cyclic compounds were found to have minogen into Lys-plasminogen. The latter has a more potent fibrinolytic activity than EACA. One higher affinity for fibrin than native plasminogen12-14 of the most suitable was AMCHA (4-aminomethyl- and promotes the preferential resolution of fibrin cyclohexanecarboxylic acid). The potency of this within a thrombus rather than causing the digestion compound, which is a mixture of stereoisomers, is of circulating fibrinogen during the fibrinolytic due to the residues in the trans-isomer, known as process. Plasmin is formed from plasminogen by tranexamic acid, which forms about 20-25%o of the further cleavage of an internal Arg-Lys peptide parent mixture.5 6 Tranexamic acid is some 7-10 bond in plasminogen.15 Plasmin also has high times more potent than EACA.7 8 It is interesting affinity for fibrin. Thus consideration of fibrinolytic that the potency of the compound depends on a inhibitors must include not only their effect at the critical distance of 7A between the essential amino- active enzyme site but also their ability to interfere and carboxylic-acid groups. with the binding of the various components. The copyright. problem is further complicated by the type of activator studied, for tissue activator has much APROTININ greater affinity for fibrin than Aprotinin (Trasylol) is a protease inhibitor derived urokinase." from bovine pancreas, parotid gland, and lung. It is a basic protein, MW 6500, with strong inhibitory Effect of EACA on caseinolysis action against kallikrein and is also an inhibitor of proteases such as plasmin. 6-Aminohexanoic acid forms reversible complexes with plasminogen causing conformational changes http://jcp.bmj.com/ Mode of action of aminocarboxylic acids in the plasminogen molecule. At concentrations of between 10-4 and 3-3 x 10-3 M 6-aminohexanoic The main action ofthe aminocaproic acid compounds acid the amount of plasmin generated by urokinase is to compete with lysine binding sites on plasmin- from plasminogen increases owing to the con- ogen and plasmin. They inhibit the activation of formational change in plasminogen. Inhibition of plasminogen by streptokinase, urokinase, and tissue preformed plasmin is noted only at a high con- activator. The binding of the heavy chain of plasmin centration of 0-1 M 6-aminohexanoic acid. 6-Amino- on September 29, 2021 by guest. Protected to fibrin monomer is achieved by lysine binding hexanoic acid increases the rate at which pro- sites. The blocking of these sites by aminocaproic teolytic degradation of Glu-plasminogen to Lys- acid causes stoichiometric inhibition of plasmin, plasminogen occurs.'6 17 The inhibitor also increases with the formation of an inactive complex between the rate at which the internal peptide bond in plasmin and aminocaproic acid.9 It will be noted plasminogen is split to form plasmin and it may be from the excellent review by D Collen (see page 24) this effect which leads to the paradoxical accelera- that the rate of binding of alpha 2-antiplasmin to tion of Glu- to Lys- plasminogen conversion in plasmin is dependent on the availability of free the presence of inhibitor. At concentrations greater lysine residues in plasmin. In the presence of free than 3-3 x 10-3 M 6-aminohexanoic acid the rate of residues plasmin is rapidly inactivated by alpha plasminogen activation by both urokinase and 2-antiplasmin. Conversely, when the lysine residues tissue activator decreases. This is due to the direct are blocked, either by fibrin monomer or by amino- effect of 6-aminohexanoic acid as a competitive caproic acid, inactivation by alpha 2-antiplasmin inhibitor of activator. J Clin Pathol: first published as 10.1136/jcp.33.Suppl_14.35 on 1 January 1980. Downloaded from

Basis of antifibrinolytic therapy 37 Effect of EACA on fibrinolysis: role of fibrin strates, but the inhibitor-kallikrein reaction is not impaired by substrate. When fibrin rather than casein is used as the The activity of aprotinin as an inhibitor depends substrate for plasmin the situation alters con- on the lysine residue at position 15, which partici- siderably. Here inhibition starts with concentrations pates in complex binding.23 Acetylation and methyla- of 6-aminohexanoic acid as low as 10-5 M when tion of the inhibitor lead to loss of its activity, tissue activator is used and 10-3 M in the presence indicating the importance of carboxyl and amino of urokinase. groups. The inhibition of plasmin by aprotinin is The greater effect of inhibition by 6-amino- stoichiometric. The inhibitor blocks an equivalent hexanoic against plasmin when fibrin rather than amount of enzyme to form an inactive complex. casein is used as substrate is due to the fact that the There is some, but inconclusive, evidence to heavy chain of plasmin possesses special binding suggest that aprotinin may have an inhibitory sites for fibrin.18 19 These sites are not utilised when action against plasminogen activator. The kinetics the substrate for plasmin is fibrinogen, lysed fibrin, of the reaction are complicated by the antiplasmin casein, or synthetic esters.18 20 6-Aminohexanoic acid action of aprotinin, and at present there is no inhibits fibrin digestion by complex formation with protein-like inhibitor able to inhibit a plasminogen- the heavy chain of plasmin preventing interaction activating enzyme under well-defined biological between the active centre in the plasmin light conditions. For instance, the inhibitors from chain and fibrin.21 Plasminogen as well as plasmin bovine organs do not impair the action of has these binding sites which are blocked by the urokinase.26 27 amino-acid inhibitors. Aprotinin is standardised in terms of kallikrein 6-Aminohexanoic acid can cause dissociation of inhibitor units (KIU) which are based on an inexact the preformed fibrin-plasminogen complex. This biological procedure in dogs. For this reason the causes separation of plasminogen from tissue inhibitory action of aprotinin against enzymes is activator which is also bound to fibrin. As plasmin- often measured on synthetic substrates. This can ogen bound to fibrin is activated more rapidly than only lead to problems since the action of an inhibitor free plasminogen it follows that dissociation by using synthetic substrates is often different from copyright. 6-aminohexanoic acid of plasminogen and fibrin that on the natural biological substrates. In practice causes a reduction in the activation rate of plasmin- the activities of a pure inhibitor standard can be ogen.9 22 The situation with regard to the effect of compared with commercial preparations.28 6-aminohexanoic acid against urokinase is different In experimental animals the in-vivo activity of since, in contrast to tissue activator, urokinase does aprotinin may easily be demonstrated. Fibrinolysis not preferentially activate plasminogen complexed can be induced in rabbits by the intravenous injection to fibrin rather than free plasminogen. of 2500 U streptokinase/kg. If 1 mg aprotinin/kg is

The inhibitory action of 6-aminohexanoic acid is injected 10 minutes before streptokinase fibrinolysis http://jcp.bmj.com/ increased in the presence of plasminogen-depleted is completely prevented. Similarly, aprotinin can plasma, which contains the natural inhibitors of inhibit an established hyperplasminaemic state in fibrinolysis. This is because the dissociation of rabbits.29 If fibrinolysis is established by an infusion plasmin from fibrin by the inhibitor releases plasmin of streptokinase causing a reduction in fibrinogen which is subsequently inhibited by the natural level and increase in clotting time the plasmin inhibitors. Probably this potentiating effect process can be reversed by intravenous injection of of 6-aminohexanoic acid on plasma inhibitors is the 5 mg aprotinin/kg. main reason for the therapeutic effect of these It must be remembered that in man treatment with on September 29, 2021 by guest. Protected drugs in inhibiting fibrinolysis. aprotinin entails injecting an animal protein and allergic reactions may occur. In general, tranexamic Mode of action of aprotinin acid is the inhibitor of choice in clinical treatment, since it is effective and relatively free from unpleasant The antifibrinolytic effect of aprotinin is due to its or toxic reactions. aztion as a non-competitive inhibitor of plasmin. Aprotinin forms complexes with several of the Classification of haemorrhage due to unopposed or serine protease enzymes23-25 and is a potent kallikrein excessive fibrinolytic activity inhibitor, reducing shock in experimental animals. The reaction is reversible and proceeds rapidly. From the clinical aspect there are four main groups Dissociation of these complexes occurs at low pH of disorders in which excessive or unopposed values of 3-4. The reaction of the inhibitor with fibrinolysis might play a role in causing haemorrhage trypsin is reduced in the presence of enzyme sub- and in which antifibrinolytic therapy might be J Clin Pathol: first published as 10.1136/jcp.33.Suppl_14.35 on 1 January 1980. Downloaded from

38 Prentice indicated.4 30 They are (I) hyperplasminaemia: blood, without , into a plain glass (a) primary fibrinolysis or hyperplasminaemia, (b) clotting tube. The hand grasped firmly around this secondary fibrinolysis as a consequence of dissemin- makes an admirable improvised incubator at 37°C. ated intravascular coagulation (DIC); (2) local The presence of non-clotting blood or a defective fibrinolysis within organs or tissues; (3) coagulation blood clot indicates that a haemostatic abnormality defects associated with normal fibrinolysis. is present. A test for accelerated lysis should then be carried out. If, as often occurs, the blood is HYPERPLASMINAEMIA incoagulable or the clot defective fibrinogen must be added. Primary fibrinlolysis or primary hyperplasminaemia In the presence of unequivocally accelerated clot In this condition excessive circulating concentrations lysis a presumptive diagnosis of hyperplasminaemia of plasminogen activator convert sufficient plasmin- may be made and treatment with antifibrinolytic ogen to plasmin to overcome plasma inhibitors. Free drugs started plus replacement blood, fibrinogen, plasmin is then able to cause digestion of haemo- and coagulation factors or as necessary. static factors such as fibrin, fibrinogen, factor V, and The use of antifibrinolytic agents in these conditions factor VIII. The combined effect of removal of can lead to dramatic clinical improvement. For fibrin plugs at the site of vascular damage together example, we saw a patient who developed generalised with depletion of coagulation factors is sufficient to bleeding with hypofibrinogenaemia after excision cause bleeding. If proteolysis is pronounced there of the rectum for malignancy. As the whole clot may be total fibrinogen depletion together with a lysis time was under 30 minutes epsilon-aminocaproic rise of fibrin degradation products (FDP), which acid was given with gratifying reversal of haemor- have an action. rhage. It is notoriously difficult to distinguish clinically Exceptionally, life threatening haemostatic break- and in the laboratory between primary fibrinolysis down may occur with such rapidity that time does and intravascular coagulation with a secondary not allow laboratory investigation. In this situation

fibrinolytic response. I agree with Merskey et al.31 initial treatment with whole blood and plasma copyright. that primary fibrinolysis is a rare event and that most components such as fibrinogen, which may be cases of defibrination are due to DIC. In DIC the conveniently given as cryoprecipitate, is given. If first priority is to treat the underlying cause of the these measures fail intravenous tranexamic acid may disorder such as or shock.32 In DIC associated be given empirically in view of the possibility of with malignancy the prognosis is often grave. In systemic hyperplasminaemia being present. Anti- obstetric accidents the main goal is to evacuate the fibrinolytic agents often provide benefits in these uterus. After that defibrination will rapidly cure patients that outweigh the risk of widespread itself with the aid of blood transfusion and clotting unlysable clot formation. However, this hazard has factor concentrates if necessary. Basu33 has recom- been noted-for instance, in the case reported by http://jcp.bmj.com/ mended antifibrinolytic drugs in the treatment of McNicol34 where EACA was given for hyperplas- obstetric defibrination on the basis that high FDP minaemia after cardiac surgery. Although control levels interfere with uterine contractibility. However, of bleeding was achieved the patient died 36 hours there is the theoretical danger that continuing later with a clotted haemopericardium and haemo- intravascular coagulation in this situation may thorax. provoke generalised thrombosis. Hyperplasminaemia may occasionally be associ- The be aware of conditions clinician should ated with tumours producing excess plasminogen on September 29, 2021 by guest. Protected causing a primary fibrinolytic state, which occur activator35 or with acute leukaemia.36 These patients particularly when tissues rich in plasminogen respond to tranexamic acid. However, they are rare activator have been handled during surgery. in comparison with patients who have underlying Operations on the prostate gland, uterus, pelvic DIC. Similarly, prostatic carcinoma either with or colon, and surgery for malignancy are liable to without surgery may cause hyperplasminaemia or primary fibrinolytic haemorrhage. If prolonged or local fibrinolytic excess leading to haematuria.37 excessive bleeding occurs after this type of operation These situations have been dealt with successfully by laboratory tests should be carried out to exclude antifibrinolytic agents. primary hyperplasminaemia. Such tests would include a count, prothrombin time, partial thromboplastin time, thrombin clotting time, and Excess fibrinolysis secondary to DIC rapid tests for fibrinogen and FDP levels. A simple Bleeding in DIC is unlikely to be due to an excessive whole blood clotting time test can be carried out in or inappropriate fibrinolytic response and anti- the operating theatre by putting some of the patient's fibrinolytic agents are not advised. Activation of J Clin Pathol: first published as 10.1136/jcp.33.Suppl_14.35 on 1 January 1980. Downloaded from

Basis of antifibrinolytic therapy 39 fibrinolysis in this situation is a secondary pro- References tective mechanism which should not be inhibited. Schwartz ML, Pizzo SV, Hill RL, McKee PA. The ORGANS effect of fibrin-stabilizing factor on the subunit LOCAL FIBRINOLYSIS WITHIN structure of human fibrin. J Clin Invest 1971;50: The individual clinical conditions where local excess 1506-13. fibrinolysis within organs may cause haemorrhage 2 Gaffney PJ, Brasher M. Subunit structure of the will be dealt with separately by others. plasmin-induced degradation products of cross- Excess local fibrinolysis is seen mainly in diseases linked fibrin. Biochim Biophys Acta 1973; 295:308-13. of the following organs: (1) uterus, causing menor- 3 Okamoto S, Nakajima T, Okamoto U, et al. A rhagia; (2) stomach and duodenum, causing surprising effect of E-amino-n-caproic acid on the gastrointestinal bleeding; (3) prostate gland, causing bleeding of dogs, produced with the activation of haematuria; (4) in the cerebrospinal fluid, after plasmin in the circulating blood. Keio J Med 1959; subarachnoid haemorrhage. 8:247-66. 4 Markwardt F. Synthetic inhibitors of fibrinolysis. In: The reason for localised haemorrhage in these Markwardt F, ed. Fibrinolytics and anti-fibrinolytics organs is that the relevant tissues are rich in plas- (Handbuch der experimentellen Pharmakologie, minogen activators (tissue activators). The response vol 46). Berlin: Springer, 1978:511-77. of tissues damaged by trauma is to release tissue Okamoto S, Okamoto U. Amino-methyl-cyclohexane- activator. The equilibrium between coagulation and carboxylic acid: AMCHA. A new potent inhibitor fibrinolysis within these tissues is disturbed with local of the fibrinolysis. Keio J Med 1962;11:105-15. production of free plasmin causing digestion of 6 Melander B, Gliniecki G, Granstrand B, Hanshoff G. haemostatic plugs. Biochemistry and toxicology of amikapron: the When tissue activator production by an organ such antifibrinolytically active isomer of AMCHA (a comparative study with E-aminocaproic acid). Acta as the prostate is sufficiently high there may be Pharmacol (Kbh) 1965 ;22:340-52. release of plasmin in the circulation leading to 7 Dubber AHC, McNicol GP, Douglas AS, Melander hyperplasminaemia. Thus the distinction between B. Some properties of the antifibrinolytically active local and general fibrinolytic excess is not absolute. isomer of amino-methylcyclohexane carboxylic acid. Fortunately, the penetration of fibrinolytic inhibitors Lancet 1964;2:1317-9. copyright. such as tranexamic acid is good, so that systemic 8 Dubber AHC, McNicol GP, Douglas AS. Amino- administration of these agents can inhibit plasmin methyl cyclohexane carboxylic acid (AMCHA), a produced at sites of organ damage without the new synthetic fibrinolytic inhibitor. Br J Haematol hazard of widespread thrombosis. It is notable that 1965;11 :237-45. the thrombotic of 9 Thorsen S. Influence of fibrin on the effect of 6- complications antifibrinolytic aminohexanoic acid on fibrinolysis caused by tissue agents are not often seen when the drugs are being plasminogen activator or urokinase. In: Davidson used for local indications such as menorrhagia, JF, Rowan RM, Samama MM, Desnoyers PC, although a few cases of thrombosis in these cir-

eds. Progress in chemicalfibrinolysis and thrombolysis, http://jcp.bmj.com/ cumstances have been reported, but rather when a vol 3. New York: Raven Press, 1978:269-83. systemic disorder of coagulation or fibrinolysis is 10 Alkjaersig N, Fletcher AP, Sherry S. e-Aminocaproic present. The exception to this is in the treatment of acid: an inhibitor of plasminogen activation. haematuria, when obstruction in the ureters or JBiol Chem 1959;234:832-7. urethra may occur due to clot formation. 1 Thorsen S, Glas-Greenwalt P, Astrup T. Differences in the binding to fibrin of urokinase and tissue plasminogen activator. Thrombos Diathes Haemorrh HEREDITARY COAGULATION DISORDERS 1972 ;28 :65-74. Coagulation defects causing haemorrhage, but with 12 Rickli EE, Otavsky WI. Release of an N-terminal on September 29, 2021 by guest. Protected a normal fibrinolytic response, are seen in haemo- peptide from human plasminogen during activation philia and other hereditary bleeding disorders. In with urokinase. Biochim Biophys Acta 1973 ;295: these circumstances any clot formed is friable and 381-4. can be disrupted by plasmin produced by normal 13 Wiman B, Wallen P. Activation of human plasminogen fibrinolytic activity. There is now good evidence that by an insoluble derivative of urokinase: structural blood loss from dental extraction and the amount of changes of plasminogen in the course of activation factor VIII transfused in may be to plasmin and demonstration of a possible inter- haemophilia mediate compound. Eur J Biochem 1973 ;36:25-31. reduced by routine use of antifibrinolytic agents 14 Thorsen S. Differences in the binding to fibrin of native before and after the operation.38 39 However, there plasminogen and plasminogen modified by pro- is insufficient evidence to justify the routine use of teolytic degradation: influence of w-aminocarboxylic antifibrinolytic drugs in haemophilia.40 The hazards acids. Biochim Biophys Acta 1975;393:55-65. of ureteric obstruction by clot after haematuria in 5 Robbins KL, Summaria L, Hsieh B, Shah RJ. The haemophilia have been reviewed.4' peptide chains of human plasmin: mechanism of J Clin Pathol: first published as 10.1136/jcp.33.Suppl_14.35 on 1 January 1980. Downloaded from

40 Prentice activation of human plasminogen to plasmin. J Biol 27 Walton PL. The hydrolysis of alpha-N-acetylgycyl-L- Chem 1967 ;242:2333-42. lysine methyl ester by urokinase. Biochim Biophys 16 Claeys H, Vermylen J. Physio-chemical and pro- Acta 1967;132:104-14. enzyme properties of NH2-terminal glutamic acid 28 Markwardt F, Richter M. Zur Standardisierung des and NH2-terminal lysine human plasminogen: Proteaseninhibitors aus Rinderorganen. Pharmazie influence of 6-aminohexanoic acid. Biochim Biophys 1969;24:620-2. Acta 1974;342:351-9. 29 Klocking HP, Markwardt F. Tierexperimendelle 17 Walther PJ, Hill RL, McKee PA. The importance of Verfahren zur Testung von Fibrinolytika und the preactivation peptide in the two-stage mechanism Antifibrinolytika. Folia Haematol 1969;92 :84-9. of human plasminogen activation. J Biol Chem 30 Prentice CRM. Indications for antifibrinolytic therapy. 1975 ;250:5926-33. Thrombos Diathes Haemorrh 1975 ;34:634-43. 18 Landmann H. Studies on the mechanism of action of 31 Merskey C, Johnson AJ, Kleiner GJ, Wohl H. The synthetic antifibrinolytics. A comparison with the defibrination syndrome: clinical features and action of derivatives of benzamidine on the fibrino- laboratory diagnosis. Br J Haematol 1967;13 :528-49. lytic process. Thrombos Diathes Haemorrh 1973 ;29: 32 Naeye RL. Thrombotic state after a hemorrhagic 253-75. diathesis, a possible complication of therapy with 19 Thorsen S, Kok P, Astrup T. Reversible and irrevers- epsilon-aminocaproic acid. Blood 1962;19:694-701. ible alterations of human plasminogen indicated by 33 Basu HK. Fibrinolysis and abruptio placentae. J changes in susceptibility to plasminogen activators Obstet Gynaec Brit Cmwlth 1969;76 :481-96. and in response to o-aminocaproic acid. Thrombos 34 McNicol GP. Disordered fibrinolytic activity and its Diathes Haemorrh 1974;32 :325-40. control. Scot Med J 1962;7:266-76. 20 Skoza L, Tse AO, Semar M, Johnson AJ. Comparative 35 Davidson JF, McNicol GP, Frank GL, Anderson TJ, activities of and polypeptide inhibitors on Douglas AS. Plasminogen-activator-producing natural and synthetic substrates. Ann NY Acad Sci tumour. Br Med J 1969;i:88-91. 1968 ;146:659-72. 36 Nilsson IM, Bjorkman SE, Andersson L. Clinical 21 Rickli EE, Otavsky WI. A new method of isolation and experiences with E-aminocaproic acid (E-ACA) as an some properties of the heavy chain ofhuman plasmin. antifibrinolytic agent. Acta Med Scand 1961 ;170: Eur J Biochem 1975 ;59 :441-7. 487-509. 22 Wallen P. Chemistry of plasminogen and plasminogen 3 Andersson L, Nilsson IM. Effect of c-amino-n-caproic activation. In: Davidson JF, Rowan RM, Samama acid (c-ACA) on fibrinolysis and bleeding conditions copyright. MM, Desnoyers PC, eds. Progress in chemical in prostatic disease. Acta Chir Scand 1961 ;121 :291-8. fibrinolysis and thrombolysis, vol 3. New York: 38 Walsh PN, Rizza CR, Matthews JM, et al. Epsilon- Raven Press, 1978:167-81. aminocaproic acid therapy for dental extractions in 23 Chauvet J, Acher R. The reactive site of basic trypsin haemophilia and Christmas disease: a double blind inhibitor of pancreas. Role of lysine 15. J Biol Chem controlled trial. Br J Haematol 1971 ;20:463-75. 1967 ;242 :4274-5. 39 Forbes CD, Barr RD, Reid G, et al. Tranexamic acid 24 Dubber AHC, McNicol GP, Uttley D, Douglas AS. in control of haemorrhage after dental extractions in In vitro and in vivo studies with Trasylol, an anti- haemophilia and Christmas disease. Br Med J coagulant and a fibrinolytic inhibitor. Br J Haematol 1972;ii:311-3. 1968;14:31-49. 40 Gordon AM, McNicol GP, Dubber AHC, McDonald http://jcp.bmj.com/ 25 Markwardt F. Naturally occurring inhibitors of GA, Douglas AS. Clinical trial of epsilon-amino- fibrinolysis. In: Markwardt F, ed. Fibrinolytics and caproic acid in severe haemophilia. Br Med J 1965; anti-fibrinolytics (Handbuch der experimentellen i:1632-5. Pharmakologie, vol 46). Berlin: Springer, 1978: 41 Prentice CRM, Lindsay RM, Barr RD, et al. Renal 487-509. complications in haemophilia and Christmas disease. 26 Lorand L, Condit EV. Ester hydrolysis by urokinase. Q J Med 1971 ;40:47-61. Biochemistry 1965 ;4:265-70. on September 29, 2021 by guest. Protected