Clinical evaluation of aprotinin

Clinical Evaluation of Aprotinin Avi Weissman and John P. Williams THE HEMOSTATIC SYSTEM

H

EMOSTASIS DEPENDS on several factors: platelets, coagulation factors, blood vessel endothelium, and fibrinolysis. The coagulation cascade represents the mechanism by which a stable fibrin clot is formed (Fig 1). Most of the coagulation factors are glycoproteins synthesized in the liver. The cascade is composed of intrinsic, extrinsic, and common pathways. Factor XII, high molecular weight kininogen, prekallikrein, and factor XI form the surface activation group. Disruption in the endothelial cell layer initiates the conversion of factor XII to factor XIIa. High molecular weight kininogen together with factor XIIa, cause transformation of prekallikrein to kallikrein and activation of factor XI to factor XIa. The end product of the intrinsic pathway is factor X conversion to Xa that is catalyzed by factor IXa and VIII. Factor X, which is the junction of both pathways, starts what is called the common pathway. Activation of factor X can be achieved via the intrinsic and extrinsic pathways. The extrinsic pathways refers to the location of these factors with regard to the vasculature. The extrinsic pathway is initiated with tissue thromboplastin (factor III) that transforms factor VII to VIIa. Factor VIIa and X then act as coinitiators with the help of platelets, phospholipids, and Ca ++, to generate Factor Xa. In the common pathway, factor Xa in combination with Ca ++, phospholipids and factor Va cleaves prothrombin to produce thrombin. Fibrin (the product of thrombin cleavage of fibrinogen) is then crosslinked to form a stable clot by factor XIIIa. Platelet function is one of the most important factors in hemostasis. The platelets that are free flowing in the blood vessels initially respond to damaged or injured vessel endothelium by adhesion. On contact, platelets release several factors that propogate further platelet activation and aggregation. Once the clot is formed, some natural fibrin breakdown occurs as part of the normal healing

process. Fibrinolysis is initiated by plasminogen, which is a serine protease synthesized by the liver. The degradation ofplasminogen is caused by tissue plasminogen activator (t-PA) and factor XIIa to plasmin. Plasmin splits fibrin or fibrinogen to produce fibrin or fibrinogen split products (Fig 2). There is normal local fibrinolysis wherever normal hemostasis occurs. Fibrinolysis is one of the most important causes of bleeding after cardiopulmonary bypass (CPB). A number of pharmocological strategies exist to inhibit excessive fibrinolysis. Epsilon Amino-Caproic Acid (EACA) and tranexamic acid (TA) are two synthetic antifibrinolytics that bind to plasminogen and plasmin (Fig 2) and inhibit the effect of plasmin on fibrin. Aprotinin is a serine protease inhibitor, which is isolated from bovine lung. Aprotinin was isolated and its activity then defined both as a kallikrein and a trypsin inhibitor in the 1930s. I APROTININ PHARMACOLOGY

Aprotinin was cleared for marketing in the United States by the Food and Drug Administration (FDA) on December 20, 1993. It is a basic (pKa 10) polypeptide comprised of 58 amino acid residues with a molecular weight of 6,512 daltons. The biochemical profile and biophysical characteristics of aprotinin are described in several reviews and the reader is referred to one of these. 2 As a serine protease inhibitor, aprotinin is able to inhibit a range of proteases with serine residues at their active site. Despite the fact that aprotinin is a natural polypeptide, its physiological role is unknown; although the compound is found in the venom of several species of snakes. 3 Aprotinin is currently supplied as a clear, odorless, sterile isotonic solution for intravenous administration.

Seminars in Anesthesia, Vo115, No 1 (March), 1996: pp 97-108

From the Department of Anesthesiology, UCLA School of Medicine, Los Angeles. CA. Address reprint requests to Avi Weissman, MD, UCLA Medical Center, Department ofAnesthesiology, 10833LeConte Ave. Los Angeles. CA 90095-1778. Copyright 9 1996 by W.B. Saunders Company 0277-0326/96/1501-000955.00/0

97

98

WEISSMAN AND WILLIAMS

Intrinsic pathway Surface A c t i v a t i o n

E~xtrlnslr Pathway T r a u m a to V e s s e l L / n / n g

XIIa

xn

Tissue Factor ~~- VIIa

VII

xi

~let

IX

Common

P h o s p h o ~

Pathway

VA CA

neys and the amount of free drug found in the urine. Because of its small size, aprotinin labeled with 99mTc is a reproducible marker for renal tubular turnover of small filtered proteins in humans. In a recent study by Levy and associates, two doses ofaprotinin were administered in continuous infusion. A three compartment model was fit to the serum concentration of aprotinin. Clearance was 35.5 m L / m i n and the volume of distribution at steady state was 26.5 L. 5

Platelet Phospholiplds

X

~Xa

Prothrombin

~ Thrombin

Fibrinogen

~.~ Fibrin

~

Stable Fibrin Clot

XIIla

HMWK = High Molecular Weight K i n i n o g e n KAL = K~1111~rein

Fig 1. Coagulation pathway.

The activity of aprotinin is expressed in kallikrein inhibitor units (KIU), which rely on measurement of biological potency. Currently the exact weight of protein (mg) or concentration in solution (mL) is expressed as an equivalent measure in KIU. Each milliliter of aprotinin contains 10,000 KIU that is 1.4 mg, or each 1 mg ofaprotinin is equivalent to 7,143 KIU. PHARMACOKINETICS

Coagulation and bleeding are of particular importance when extracorporeal circulation is involved as in most cardiac operations. The attempt to decrease the a m o u n t of homologous blood products given to patients led to a search for drugs that would enable us to achieve this goal. Aprotinin is inactive when given orally.l The half-life in the plasma is biphasic with an initial elimination half-life of approximately 1 hour. Aprotinin needs to be administered as a continuous infusion to maintain a constant plasma concentration. The drug is principally cleared by the kidney, where it is filtered in the glomeruli and sequestered by the proximal tube cells for many hours. 4 Thus, some discrepancy is noted between the a m o u n t of drug deposited in the kid-

PHARMACODYNAMICS

The exact mechanism by which aprotinin decreases bleeding is unclear. A number of studies suggest that decreased fibrinolysis, protection of platelet function, and decreased activation of coagulation cascade are all important in the amelioration of postoperative bleeding.

Platelet Dysfunction Platelet dysfunction during bypass is secondary to several mechanisms, 6 among them are: decreased numbers during the first few minutes on CPB, increased aggregation and decreased adhesiveness. Aprotinin decreases platelet aggregation, 7 which causes an increase in the number of platelets post-CPB. The mechanism by which platelets aggregate or adhere to assist in clot formation is a complicated one. Tabuchi and associates 8 indicated that the protection ofplatelet adhesive capacity during CPB is the main function of aprotinin. In their study, there was no evidence for an enhancement of the extrinsic clotting pathway. Increases in glycoprotein Ib and platelet von Willebrand Factor (two factors which are responsible for modulating platelet adhesiveness) were two of the suggested mechanisms to

Plasminogen

BloodActivators UrokinasePlasminogen

Tranexamlc Acid E-aminocaproic Acid

Activator

Streptok~lase Tissue Plasminogen Activator Plasmin

Thrombin

~

Fibrinogen Fibrin

Fig 2. Fibrinolysis pathway.

Fibrin Split Products

CLINICAL EVALUATION OF APROTININ

augment coagulation post-CPB. 9'~~Alternatively, Orchard and associates ~1 found no difference in platelet function or number in aprotinin treated patients post-CPB. Other mechanisms suggested are related to a decrease in the binding of heparin to platelets ~2that is modulated by aprotinin. Although aprotinin is included as an antifibrinolytic (with EACA and TA), it is unclear if this effect is the primary mechanism which decreases bleeding and improves coagulation postoperatively.

Fibrinolysis Fibrinolysis, or the breakdown of fibrin to form fibrin split products is enhanced by plasmin. Several proteases increase the level of plasmin such as t-PA and urokinase plasminogen activator (Fig 2). The antifibrinolytic effect of aprotinin during liver transplantation is via the inhibition oft-PA, but not urokinase plasminogen activator. ~3 As the levels of t-PA are decreased, there is a concommitant decrease in plasmin level and a subsequent decrease in the rate of fibrinolysis. Aprotinin at low levels, also shows a direct inhibitory effect on plasmin (plasma concentration of 50 KIU/mL) which may reduce postoperative bleeding. In addition, at high plasma concentrations of aprotinin (>200 KIU/mL), plasma kallikrein is inhibited. This reduces the activation of the contact phase system that initiates the intrinsic coagulation pathway (Fig 1). The contact activation phase occurs at the point where factor XII and XI activate factor IX. ~4t6 In summary, aprotinin is a serine protease inhibitor that was discovered by chance. It was first used during CPB to inhibit plasmin-induced

99

complement activation and found to cause significant reduction of blood loss and blood requirements. Subsequent investigations showed an improvement in hemostasis associated with "protection" of the platelet adhesive receptor (Gp Ib) at the onset of CPB. Without aprotinin, the contact phase system of coagulation is activated on initial passage through the CPB circuit. Subsequent activation of the intrinsic pathway causes thrombin formation, which impairs platelet adhesiveness. Aprotinin blocks contact activation of the kallikrein system during CPB and in synergy with heparin prevents thrombin formation. CLINICAL APPLICATION

Cardiac Surgery Many outcome studies are being performed to evaluate the effectiveness ofaprotinin in reducing perioperative blood loss during cardiac surgery. The effectiveness of aprotinin in patients undergoing coronary artery bypass graft (CABG) surgery has been well established. In an initial study ]7 from the early 1980s, aprotinin was evaluated as an anti-inflammatory agent to prevent pulmonary damage during CPB. A serendipitous finding was significantly less blood loss in the aprotinintreated patients (about 300 mL) in comparison with the control group. A subsequent study by Royston ~8 investigated the effect of aprotinin on the need for blood transfusion after repeat open heart surgery. This group of patients is at higher risk for postoperative bleeding. Homologous blood transfusion requirements were six times greater in the control group (1,500 mL in comparison with the aprotinin-treated group 286 mL, P < .001).

Table 1. Suggested Aprotinin Regimen Dosing

Test Dose

Loading Dose

High dose full Hammersmith

10 min. before loading dose 1.4 mg (I 0,000 KIU*)

before incision over 20-30 min. 280 mg (2,000,000 KIU)

Low dose half Hammersmith

1.4 mg (I 0,000 KIU)

140 mg (! ,000,000 KIU)

Timing

Abbreviation: KIU, kallikrein Inhibitor units.

Pump Prime Dose mixed in pump prime 280 mg (2,000,000 KIU) 140 mg ( 1,000,000 KIU)

Continuous Infusion after loading dose to end of surgery 70 mg/h (500,000 KIU)

35 mg/h (250,000 KIU)

100

Several aprotinin dosing regimens (Table 1) evolved from these studies. The most commonly used algorithm today is the high dose aprotinin, also known as "Full Hammersmith" named for the hospital where the algorithm was designed. This dose is higher than the initial studies because in these studies the dose was chosen to inhibit the inflammatory response and not specifically to prevent bleeding. The "Full Hammersmith" regimen is initiated by a test dose of 10,000 KIU (1.4 mg) followed by a loading dose of 2,000,000 KIU (280 mg) over 20 minutes before incision followed by a continuous infusion at a rate of 500,000 KIU/hr (70 mg/hr) until the end of surgery; in addition, a one time pump prime dose of 2,000,000 KIU (280 mg) is required. Recent aprotinin studies concentrated on five major areas: optimal dosing regimens, comparison to other strategies for reducing homologous transfusions, cost effectiveness, delineating major side effects, and the effect on the coagulation cascade. After the initial studies in Europe, follow-up clinical studies were initiated in North America. Three of them were considered by the FDA for approval of this drug in the United States and are reviewed below. The first study was conducted in the Cleveland Clinic by Cosgrove et al.19 This double-blind clinical trial tested the efficacy a n d safety of aprotinin in 169 patients undergoing isolated reoperative myocardial revascularization. One group used high-dose aprotinin, another low-dose aprotinin, and the third received placebo treatment. Treatment groups did not differ significantly with respect to age, gender, red cell mass, number of grafts, use of internal mammary artery, or incidence ofperioperative aspirin therapy. Patients treated with aprotinin had a significant reduction in postoperative chest tube drainage and transfusion requirements. Fewer aprotinin-treated patients received red blood cell transfusions (high dose = 42%; low dose = 41%; placebo = 77%; P = .001 for placebo v high dose). The average total dose transfused in the high-dose group was 1.8 units; in low dose group, 2.0 units; and in the placebo group, 3.5 units (P = .001 placebo v high dose). A similar reduction in both chest tube drainage and transfusion requirements was seen in patients using aspirin.

WEISSMAN AND WILLIAMS

However, some safety issues were raised by the investigators regarding increased risk for myocardial infarction (high dose 22% v placebo 13%; P = .387) and renal failure. The second North-American trial was the multi-center CABG study conducted in five centers (University of Iowa, The Mayo Clinic, University of Illinois, Deborah Heart and Lung Center, and the University of Chicago) and reported by Lemmer and coinvestigators. 2~This study also included early vein graft patency assessment by ultrafast computed tomography. A total of 216 patients were randomized at 5 centers to receive either high-dose aprotinin or placebo. The patients were further stratified by primary or repeat CABG procedures. In the primary group, homologous blood exposure was 2.2 units per patient in the aprotinin group versus 5.7 units per patient in the placebo (P = .01). In the repeat CABG group, the results were more striking, 0.3 units per patient for the aprotinin versus 10.7 units per patient in the placebo group (P < .001). Mortality was slightly higher 5.6% versus 3.7% in the aprotinin group (P = .517). The diagnosis of myocardial infarction was made clinically in 8.9% of the patients receiving aprotinin as compared with 5.6% of patients receiving placebo (P = .435) in the primary surgery group. In the repeat surgery group, a 10.3% rate of myocardial infarction was seen compared with an 8.3% rate for patients receiving placebo (P = 1.0). Further analysis of the electrocardiogram and cardiac enzymes showed no significant difference between the two groups. The ultrafast computed tomography showed no statistical difference in graft patency (95% for placebo in comparison with 92% in the aprotinin group). This study showed no statistical difference in adverse events with respect to mortality, myocardial infarction, or renal dysfunction. The third North-American clinical study was performed by Murkin et al2~ at the University cf Western Ontario, Canada. This double-blind, randomized, placebo-controlled study examined the efficacy of high dose aprotinin in patients who received aspirin within 48 hours before either a CABG or valvular heart operation. Patients treated with aprotinin (29) had significantly lower total blood loss (1,409 _+ 232 mL v 2,765 _+ 248 mL) P = .0002. Fifty-nine percent (17) of the patients treated with aprotinin required red blood

CLINICAL EVALUATION OF APROTININ cell transfusion versus 88% (22) in the placebo group. The incidence of complications, including myocardial infarction, was similar in both groups. In addition to these three North-American studies, a recent study from London, England examined low-dose aprotinin versus placebo in a randomized, double-blind, placebo-controlled study. Seventy-nine patients undergoing primary, elective cardiac surgery were consecutively allocated to one of three groups. Group K (n = 27) received 1,000,000 KIU into the pump prime. Group L (n = 27) received aprotinin bolus of 500,000 KIU after induction of anesthesia with an additional 1,000,000 KIU added to the prime pump. Group J received 0.9% saline (placebo). Both aprotinin treated groups showed significantly less postoperative blood loss than controls (P < .001). 2ja

These more recent studies serve as confirmation of the European studies from the 1980S. i7"22"25 Other, similarly confirming studies are available for review. A double-blind study was carried out in Leeds, United Kingdom, comparing aprotinin with placebo in patients undergoing reoperation for heart valve replacement. The results of this study confirmed the effectiveness ofaprotinin at reducing blood loss associated with CPB.~ I The largest series of patients (n = 1,784) is from Munich, West Germany. This group confirmed that aprotinin significantly decreases both blood loss and hemologous blood transfusions in comparison with placebo. 23 Furthermore, there was no significant difference in renal dysfunction between the two groups.

Monitoring of Coagulation on Coronary Bypass Heparin is commonly used to ablate the systemic coagulation process. Heparin binds to and activates Antithrombin III (AT III) which, in turn, irreversibly binds to thrombin and inactivates it; suppressing further coagulation and clot formation.26 The heparin/AT III complex increases the activity of AT III almost a thousandfold, effectively neutralizing all thrombin in the blood. This is a vital component of CPB because it prevents clot from forming when blood is exposed to the surface on the extracorporeal circuit. The inhibition of thrombin is terminated at the end of CPB in order to restore normal coagulation and prevent postoperative bleeding. This heparin

101 effect is inhibited with protamine. Protamine acts by forming a large complex with heparin thus neutralizing its action. In many hospitals, the activated clotting time (ACT) is used to monitor the level of anticoagulation with heparin. The common accepted level of adequacy is achieved when a celite ACT is maintained above 400 seconds. 27 However, several recent studies argue that this level is not valid when aprotinin is administered. The two machines commonly used for ACT measurement are the Hepcon/HMS System (Medtronic Hemo Tec, Englewood, CO) that uses kaolin for contact system activation and the Hemochron (International Technidyne Corporation, Edison, N J) that uses both celite and kaolin. These two activators result in highly significant differences in ACT results when aprotinin is added. The kaolin-based activator was not effected by aprotinin throughout surgery while the celite clotting time almost doubled when as heparin and aprotinin were combined. 2s'29 This is not a new observation; however, a potentially lethal error results if the dose of heparin is lowered based on a celite ACT. The Cleveland Clinic study headed by Cosgrove 19 noted a higher incidence of early graft closure in the aprotinin-treated patients. One of the reasons for this observation could be the maintenance of a celite-based ACT during CPB at the 400 second level. The interaction of aprotinin and heparin results in a lower than normal heparin level at any ACT. In 1994, Tabuchi and associates compared the celite ACT with highdose thromboplastin and high-dose thrombin time (HiTT) and found that both HiTT and highdose thromboplastin were not affected by the addition of aprotinin. When aprotinin was used, these two two tests provide more reliable measures of heparin level and effect during CPB. 3~ Despotis compared the effect ofaprotinin on the ACT, with blood and plasma heparin measurements. He concluded that whole blood heparin measurement was unaffected by aprotinin and correlated well with plasma anti-Xa heparin measurement. Therefore, the automated protamine titration assay can be used to monitor heparin concentrations accurately in patients receiving aprotinin. 31 In aprotinin-treated patients, protamine neutralizes the anticoagulant effect of heparin but

102

W E I S S M A N A N D WILLIAMS

not the many effects of aprotinin. Therefore, at the conclusion of CPB, protamine reversal is based on heparin effect as measured by the kaolin ACT or the H i T T tests, but not on a celite ACT. At very high concentrations of aprotinin, even the kaolin ACT may not be reliable. Therefore, if kaolin ACT is used to measure heparin effect, the loading dose of aprotinin should administered over 20 to 30 minutes. (Table 2) In summary, there are several ways to monitor adequate heparinization after the concommitant administration of aprotinin. Maintaining the celite ACT > 750 seconds or using a kaolin ACT with the caveat of extending the initial aprotinin dose over 20 to 30 minutes or using the H i T T may be chosen. Finally, a fixed dose regimen, in which the heparin dose is administered according to protocol that is time dependent and dosing does not depend on any measure of effect may be chosen. Such a regimen based on data from a 1981 study by Culliford and associates showing that there is poor correlation between heparin concentration and ACT even in the absence of aprotinin. 32 Some of the pros and cons of these methods are explained in Table 1. One final issue when combining the use of aprotinin and heparin regards emergent heparinization requirements after the administration of protamine. Bailey et al examined this issue in a randomized, placebo-controlled study where heparin requirements nearly doubled after treatTable 2.

Mode of action

Change with aprotinin

Detect heparin resistance Provides baseline, preheparin or postheparin control Accepted level with heparin and aprotinin

ment with aprotinin. In an attempt to explain this finding, the authors measured blood protamine levels; however, there was no increase beyond normal. Alternatively, aprotinin may act as a substrate for the N-carboxypeptide that destroys protamine, thus indirectly enhancing and prolonging the activity of protamine. 33 OUTCOME COMPARISONS

Three antifibrinolytic agents are currently available to decrease both blood loss and the use of homologous blood transfusions after CPB. EACA and TA are both synthetic antifibrinolytics that are proven effective. The preferred measurement of outcome is the amount of homologous blood products received by the patient. A decrease in measured blood loss or an altered coagulation profile are convenient monitors of effect but do not necessarily relate to an improvement in outcome. Two recent studies compared EACA with either TA or aprotinin. Trinh-Duc et al, found no difference in either measured blood loss or homologous transfusion requirements between a high-dose aprotinin group and an EACA group. Sixty patients were allocated in a randomized, prospective manner to one of the two active groups; but there was no placebo group. 34 The financial implications of this study are as impressive as the medical because EACA is about 50 times less expensive than aprotinin. When TA

Approaches to Heparin Monitoring With Aprotinin Use

Celite-ACT

Kaolin-ACT

Fixed Dose

HiTT

Measures heparin effect using celite as activating substance Prolonged

Fixed doses of heparin are given on a schedule doesn't depend on ACT N/A

Measures time to clot in the presence of thrombin, used for high dose heparin

Yes Yes

Measures heparin effect using kaolin as activating substance Only at very high plasma levels of aprotinin Yes Yes

N/A N/A

Yes No

>750 seconds

>400 seconds

N/A

150-250 seconds for heparin concentration of 35 #lmL

Abbreviations: ACT, activated clotting time; HiTT, high-dose thrombin time; N/A, not applicable.

None

CLINICAL EVALUATION OF APROTININ

and aprotinin were compared, aprotinin significantly reduced both blood loss and the incidence of homologous transfusions in comparison with a placebo group (P < .05). In contrast to EACA, TA did not differ from placebo or the aprotinin group. Other nonfibrinolytic measures of effect such as plasma antiplasmin activity were equally depressed in both the TA and aprotinin groups. This suggests that aprotinin was more efficacious than TA in "nonfibrinolytic act of protecting platelet function against attack by plasmin during CPB. ''35 The prophylactic administration of EACA in patients undergoing first time coronary artery bypass grafting results in a significant decrease in blood loss and blood transfusion requirements. 36 There are several studies that document the efficacy ofTA, EACA, and aprotinin individually, but very few studies comparatively. The few available show no significant difference between agents, l-desamino-8-D-arginin vasopresin (DDAVP) was compared with aprotinin in a recent study in Spain. 37 The conclusion of this study showed that aprotinin inhibits fibrinolysis in that there was significantly less fibrin split product in the aprotinin group in comparison with the DDAVP group. Moreover, neither of the DDAVP groups showed any beneficial effect.35,38.39 CONGENITAL REPAIRS Aprotinin is used in children undergoing cardiac surgery with CPB. Several prospective studies are available from Europe. The major issues of concern were selecting an effective dose of aprotinin while avoiding severe complications. Excessive hemorrhage after CPB in the pediatric population is secondary to both platelet dysfunction and fibrinolysis. Boldt et al in a randomized, prospective manner compared aprotinin with placebo and noted a significant reduction in platelet aggregation across all groups. The aprotinin dose used here was 25,000 Kallikrein inhibitory unit (u)/kg after induction, 28,000 u/kg on pump prime, and 25,000 u/kg as a drip every hour on CPB. Treatment with aprotinin neither improved platelet function nor decreased postoperative blood loss. 4~ In contrast, two studies from Turkey and Brazil showed a significant decrease in blood loss and homologous transfusion requirements in an

103

aprotinin treated group in comparison with placebo. Both centers used high-dose aprotinin: 50,000 u/kg (7 mg/kg) and that may have contributed to the difference in r e s u l t s . 41'42 The Turkish and Brazilian studies included 20 and 30 patients respectively. Impairment of renal function was examined by Rannori et al from the University of Milan. In their study, two groups of children undergoing cardiac surgery (between 15 days to 6 years of age) were randomized to receive either low-dose aprotinin (30,000 u/kg on prime solution) or placebo. There were signifiant differences in blood loss and homologous transfusion requirements; however, these investigators also found increased levels of blood urea nitrogen and creatinine for up to 24 hours postsurgery. Their suggestion that higher aprotinin doses (>30,000 units/kg) may be more effacacious is tempered by the evidence of a moderate tubular function impairment. 43 DEEP HYPOTHERMIC CIRCULATORY ARREST

There is limited clinical observation in patients undergoing deep hypothermic perfusion with or without circulatory a r r e s t . 44'45 In one study, greater bleeding, as well as a higher incidence of thrombosis and death, was recorded in the aprotinin-treated patients. Furthermore, there are several reports of severe coagulation disturbances when aprotinin is combined with deep hypothermic circulatory arrest, up to and including disseminated intravascular coagulation (DIC). One of the mechanisms suggested for these clotting disorders suggests that aprotinin inhibits the protease enzymes which maintain the fluid state of the blood during hypothermic low flow and arrest states. The second most widespread use of aprotinin in surgery is probably in orthotopic liver transplantation (OLT). Bleeding complications frequently occur during OLT, particularly in patients with liver cirrhosis and a subsequent decrease in production of all the enzymes responsible for coagulation and fibrinolysis. Enhanced fibrinolytic activity in plasma seems to play a key role in the development of this intraoperative hemorrhage. One possible mechanism is attributed to high plasma levels of t-PA after graft reperfusion. Aprotinin-treated patients showed lower levels of t-PA on graft reperfusion

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WEISSMAN AND WILLIAMS

than a placebo group (P < .05). There was also a decrease in D-dimer levels and an increase in antiplasmin activity (P < .05 for both).~3 A retrospective study by Smith was carried out on 60 patients undergoing OLT. Patients were divided into three g r o u p s . 46 Group ! patients received aprotinin but were without cirrhosis. Group II patients had cirrhosis and did not receive aprotinin. Group III patients had cirrhosis and received aprotinin. The amount of blood loss and homologous transfusion requirements were similar in the noncirrhotic group and the cirrhotic group receiving aprotinin. Both of these groups, I and III, required significantly fewer homologous transfusions than those in the cirrhosis group that did not receive aprotinin. Patrassi, et al also found similar results. His study was also retrospective but resulted in the recommendation that aprotinin be infused during OLT in all cirrhotic patients.47 The only prospective study in OLT patients receiving aprotinin dealt with a comparison of low and high doses. In the high-dose group (n -- 94), an initial dose of 2,000,000 KIU was followed by an infusion of 500,000 KIU/hr until the conclusion of surgery. In the low-dose group (n = 95) an initial dose of 500,000 KIU was followed by an infusion of 150,000 KIU/hr. There was no difference between the two groups in their homologous transfusion requirements. Other antifibrinolytics (EACA and TA) are used routinely in OLT and may also reduce blood loss. However, a comparison of the effect of aprotinin and the other antifibrinolytic agents is still awating a large randomized, double-blind prospective study.47a OTHER APPLICATIONS

Thrombocytopenia Patients with thrombocytopenia may benefit from aprotinin particularly during cardiac surgery. Roath et al described five patients with thrombocytopenia of various causes.48 Aprotinin was effective in controlling bleeding in all five patients, which suggests the need for more controlled studies in these patients.

models for corneal defect, none have proven to be satisfactory.

Infectious Disease Enzymatic degradation ofaprotinin yields five oligopeptide fragments. Two fragments show both antiviral and antibacterial activities. Two fragments showed only antiviral activity and one fragment showed no antimicrobial activity. Of the former two oligopeptides, one showed antiviral activity against human herpes simplex virus type I and bovine parainfluenza virus type 3. An identical synthetic peptide had the same antiviral spectrum as the natural hexapeptide but showed no antimicrobial activity. Intact aprotinin is ineffective against viruses, but possesses anti-bacterial properties against several bacterial species.5~ In a study conducted in Russia, aprotinin was reported to show activity against the parainfluenza virus. 5~

Pancreatitis A multicenter, double-blind trial was performed on 78 patients with severe acute pancreatitis. One group was treated with intraperitoneal high-dose aprotinin. There was no difference in mortality between the aprotinin treated and the nonaprotinin-treated group. However, in the group not treated with aprotinin, six patients underwent operative intervention following pancreatic necrosis: this compared to none in the treated group. The conclusion of this study was that aprotinin decreases the incidence of pancreatic necrosis. 5~a

Orthopedic Surgery Patients undergoing knee or hip replacement had decreased blood loss and required fewer homologous transfusions with aprotinin use. 52'53

Dental Aprotinin reduces postoperative pain and swelling after dental surgery (third molar). The mechanism for this observation probably involves with the inhibitory effects of aprotinin on chemical mediators of acute inflammation.54

Ophthalmology

Neurosurgery

Several researchers examined the effect of aprotinin in the prevention of recurrent corneal epithelial defects in rabbits. 49 There are several

A single case report from England described a patient undergoing intracranial surgery whose DIC was controlled with aprotinin. After admin-

CLINICAL EVALUATION OF APROTININ

istration of high dose aprotinin, hemorrhaging was controlled and the measured hyperfibrinolytic state reversed. Blood samples suggested an increase in local levels oft-PA. 5s COMPLICATIONS

Aprotinin is a basic serine protease inhibitor. As such is it physically incompatible with a number of compounds including the amino acid solutions and lipid emulsions used in parenteral nutrition, corticosteroids, and tetracycline. Aprotinin also serves as an antidote to an overdose (relative or absolute) of t-PA or streptokinase used as thrombolytics. I There arc several descriptions in the literature concerning possible complications related to aprotinin. The major ones involve renal failure, allergic reactions, or thrombotic events including early coronary graft occlusion.

Renal Function Initial studies showed that aprotinin is taken up by the proximal tubular cells and retained there for many hours. 4 There is some concern that renal function is affected by the presence of high blood concentrations of aprotinin. A retrospective study conducted in Italy, showed increases in both BUN and creatinine with aprotinin after pediatric cardiac surgery. However, two prospective North-American studies using a randomized, double-blind, placebo-controlled approach showed no difference in renal function. 20,56 Thrombotic Events The antifibrinolytic and platelet stabilizing effect of aprotinin raises numerous concerns regarding hypercoagulable state. Several studies show thrombotic phenomena attributable to aprotinin. In a Cleveland Clinic study, 19patients receiving aprotinin showed an increased rate of coronary graft thrombosis (postmortem assessment). Other assessments of graft patency (ie, ultrafast computed tomography scan) showed similar results, s6 Alternatively, several prospective, double-blind, placebo-controlled studies showed no difference in the incidence of graft occlusion between treated and placebo patients. 2~ There are other types of case reports regarding thrombotic events associated with the use of aprotinin including early formation of thrombi on pul-

105

monary artery catheters, 59 and a fatal thrombotic complication during liver transplantation. 6~

Allergic Reactions Aprotinin is a polypeptide derived from bovine lungs. It has the potential to cause adverse allergic phenomena. Anaphylactic reactions require previous exposure to the antigen (drug) and then generation of antigen-specific IgE. The number of patients today with previous aprotinin exposure is still small; however, with increasing use of the drug, the magnitude of the problem will increase. There are a few case reports ofanaphylactic shock and even death after re-exposure. 61"64a Biological tissue sealant is used for facilitating intraoperative hemostasis. It is composed of many agents including aprotinin. Kon, described seven anaphylactic shock events occurring immediately after the topical application of this biological tissue sealant. Several interesting publications regarding topical use of aprotinin intraoperatively showed mixed results as far as efficacy of decrease in blood requirement. 65'66 IgE antibodies specific for aprotinin were found to be the cause of the reaction in all cases. In most cases the allergic reaction occurred after reexposure to intravenous aprotinin; however, aprotinin is contained in many biological sealants. It is increasingly likely that we will encounter adverse reactions without receiving a history of previous exposure to aprotinin. Current recommendations are to give a 1 mL test dose then wait l0 minutes before starting the loading dose. However, skin testing with diluted aprotinin may become necessary in patients known to have had previous aprotinin therapy. SUMMARY

The use of homologous transfusions has received tremendous publicity in the last l0 years mainly because of public hysteria regarding human immunodeficiency virus. However, numerous other transfusion risks, including ABO type and subtype incompatibility, hepatitis, sepsis, febrile reactions, immune suppression, and viral transmission far outweigh the risk of transmission of human immunodeficiency virus. Aprotinin is known to decrease postoperative blood loss and homologous transfusion requirements when administered prophylactically before CPB and OLT. However, several unanswered questions

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remain about the selection of patients. The improvement noted orthopedically is greater for reoperations than primary procedures. Furthermore, there are few studies that compare other antifibrinolytics (ie, EACA, TA) with aprotinin. Aprotinin is about 50 times more expensive than EACA and about 5 to 10 times more expensive than TA. If aprotinin is used as a strategy during CPB, the issue of monitoring for heparinization is critical. Any one of four methods discussed in this article are safe: celite ACT maintained at >750 seconds, kaolin ACT >400, the HiTT test, or a fixed dose regimen. Aprotinin is used widely in Western Europe and there are few untoward effects published. The observation of an increased risk for thrombosis requires closer scrutinization. It is imperative that each institution determine the subset of patients likely to benefit from prophylactic therapy and to confirm that the treatment is not associated with an increased incidence of adverse reactions before engaging in the routine use of aprotinin. REFERENCES 1. Royston D: High-dose aprotinin therapy: A review of the first five years' experience. J Cardiothorac Vasc Anesth 6: 76-100. 1992 2. Fritz H. Wunderer G: Biochemistry and applications of aprotinin, the kallikrein inhibitor from bovine organs. Arzneimittelforschung 33:479-494. 1983 3. Laskowski M J, Kato I: Protein inhibitors ofproteinases. Annu Rev Biochem 49:593-626. 1980 4. Tenstad O. Williamson HE, Clausen G. et al: Glomerular filtration and tubular absorption of the basic polypeptide aprotinin. Acta Physiol Scand 152:33-50. 1994 5. Levy JH, Bailey JM. Salmenpera M: Pharmacokinetics of aprotinin in preoperative cardiac surgical patients. Anesthesiology 80:1013-1018. 1994 6. Hennesy Jr VL, Hicks RE, Niewiarowski S. et al: Function of human platelets during extracorporeal circulation. Am J Physiol 232:H622-H628, 1977 7. Mohr R, Goor DA, Lusky A, et al: Aprotinin prevents cardiopulmonary bypass-induced platelet dysfunction. A scanning electron microscope study. Circulation 86:11405II409. 1992 8. Tabuchi N. De Haan J, Boonstra PW, et al: Aprotinin effect on platelet function and clotting during cardiopulmonary bypass. Eur J Cardiothorac Surg 8:87-90. 1994 9. KaUis P. Tooze JA. Talbot S. et al: Aprotinin inhibits fibrinolysis, improves platelet adhesion and reduces blood loss. Results of a double-blind randomized clinical trial. Eur J Cardiothorac Surg 8:315-322 (discussion 22-23), 1994 10. Havel MP, Griesmacher A, Weigel G, et al: Aprotinin increases release of von Willebrand factor in cultured human umbilical vein endothelial cells. Surgery 112:573-577, 1992

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CLINICAL EVALUATION OF APROTININ 28. Wendel HP, Heller W, Gallimorc M J, et al: The prolonged activated clotting time (ACT) with aprotinin depends on the type of activator used for measurement. Blood Coagul Fibrinolysis 4:41-45, 1993 29. Wang JS, Lin CY, Hung WT, et al: Monitoring ofheparin-induced anticoagulation with kaolin-activated clotting time in cardiac surgical patients treated with aprotinin. Anesthesiology 77:1080-1084, 1992 30. Tabuchi N, Nip TL, Tigchelaar I, et al: Monitoring of anticoagulation in aprotinin-treated patients during heart operation. Ann Thorac Surg 58:774-777, 1994 31. Despotis GJ, Joist JH, Joiner-Maier D, et al: Effect of aprotinin on activated clotting time, whole blood and plasma heparin measurements. Ann Thorac Surg 59:106-111, 1995 32. Culliford AT, Gitei SN, Starr N, et al: Lack of correlation between activated clotting time and plasma heparin during cardiopulmonary bypass. Ann Surg 193:105-111, 1981 33. Bailey CR, Fisher AR, Wieiogorski AK: Reheparinisation requirements after cardiopulmonary bypass in patients treated with aprotinin. Br Heart J 72:442-445, 1994 34. Trinh-Duc P, Wintrebert P, Boulfroy D, et al: [Comparison of the effects of epsilon-aminocaproic acid and aprotinin on intra- and postoperative bleeding in heart surgery] Comparaison des effets de racide epsilon-aminocaproique et de raprotinine sur le saignement per- et post-operatoire en chirurgie cardiaque. Ann Chir 46:677-683, 1992 35. Blauhut B, Harringer W, Bettelheim P, et al: Comparison of the effects of aprotinin and tranexamic acid on blood loss and related variables after cardiopulmonary bypass. J Thorac Cardiovasc Surg 108:1083-1091, 1994 36. Daily PO, Lamphere JA, Dembitsky WP, et ai: Effect of prophylactic epsilon-aminocaproic acid on blood loss and transfusion requirements in patients undergoing first-time coronary artery bypass grafting. A randomized, prospective, double-blind study. J Thorac Cardiovasc Surg 108:99-106, 1994; discussion 106-. 37. Rocha E, Hidalgo F, Llorens R, et al: Randomized study of aprotinin and DDAVP to reduce postoperative bleeding after cardiopulmonary bypass surgery. Circulation 90:927-927, 1994 38. Longstaff C: Studies on the mechanisms of action of aprotinin and tranexamic acid as plasmin inhibitors and antifibrinolytic agents. Blood Coagul Fibrinolysis 5:537-542, 1994 39. Pipan CM, Giasheen WP, Matthew TL, et al: Effects of antifibinolytic agents on the life span of fibrin sealant. J Surg Res 53:402-407, 1992 40. Boldt J, Knothe C, Zickmann B, et al: Aprotinin in pediatric cardiac operations: Platelet function, blood loss, and use of homologous blood. Ann Thorac Surg 55:1460-1466, 1993 41. Hazan E, Pasaoglu I, Demircin M, et al: The effect of aprotinin (trasylol) on postoperative bleeding in cyanotic congenital heart disease. Turk J Pediatr 33:99-109, 1991 42. Herynkopf F, Lucchese F, Pereira E, et al: Aprotinin in children undergoing correction of congenital heart defects. A double-blind pilot study. J Thorac Cardiovasc Surg 108: 517-521, 1994 43. Ranucci M, Corno A, Pavesi M, et al: Renal effects of low dose aprotinin in pediatric cardiac surgery. Minerva Anesthesiologica 60(7-8):361-366, 1994

107 44. Saffitz JE, Stahl D J, Sundt TM, et al: Disseminated intravascular coagulation after administration of aprotinin in combination with deep hypothermic circulatory arrest. Am J Cardiol 72:1080-1082, 1993 45. Westaby S, Forni A, Dunning J, et al: Aprotinin and bleeding in profoundly hypothermic peffusion. Eur J Cardiothorac Surg 8:82-86, 1994 46. Smith O, Hazlehurst G, Brozovic B, et al: Impact of aprotinin on blood transfusion requirements in liver transplantation. Transfus Med 3:97-102, 1993 47. Patrassi GM, Viero M, Sartori MT, et al: Aprotinin efficacy on intraoperative bleeding and transfusion requirements in orthotopic liver transplantation. Transfusion 34:507511, 1994 47a. Soilleux X, Gillon MC, Mirand A: Comparative effects of small and large aprotinin doses on bleeding during orthotopic liver transplantation. Anesth Anal 80:349-352, 1995 48. Roath OS, Majer RV, Smith AG: The use ofaprotinin in thrombocytopenic patients: A preliminary evaluation. Blood Coagul Fibrinolysis 1:235-237, 1990 49. Boisjoly HM, Sun R, Giasson M, et al: Topical fibronectin and aprotinin for keratectomy wound healing in rabbits. Arch Ophthalmol 108:1758-1763, 1990 50. Peilegrini A, Thomas U, Franchini M, ct al: Identification of an aprotinin antiviral domain. FEBS Lett 344:261265, 1994 51. Zhirnov OP, Golyando PB, Ovcharcnko AV: Replication of influenza B virus in chicken embryos is suppressed by exogenous aprotinin. Arch Viroi 135:209-216, 1994 51a. Befling R, Genell S, Ohlsson K: High-dose intraperitoncal aprotinin treatment of acute severe pancreatitis: A double-blind randomized multi-center trial. Gastroenterol 29: 479-485, 1994 52. Thorpe CM, Murphy WG, Logan M: Use ofaprotinin in knee replacement surgery. Br J Anaesth 73:408-410, 1994 53. Murkin JM, Shannon NA, Bourne RB, et al: Aprotinin decreases blood loss in patients undergoing revision or bilateral total hip arthroplasty. Anesth Analg 80:343-348, 1995 54. Brennan PA, Gardiner GT, McHugh J: A double blind clinical trial to assess the value of aprotinin in third molar surgery. Br J Oral Maxillofac Surg 29:176-179, 199 l 55. Palmer JD, Francis DA, Roath OS, et al: Hyperfibrinolysis during intracranial surgery: Effect of high dose aprotinin. J Neurol Neurosurg Psychiatry 58:104-106, 1995 56. Laub GW, Riebman JB, Chen C, et al: The impact of aprotinin on coronary artery bypass graft patency. Chest 106: 1370-1375, 1994 57. Bidstrup BP, Underwood SR, Sapsford RN, et al: Effect ofaprotinin (Trasylol) on aorta-coronary bypass gra~ patency. J Thorac Cardiovasc Surg 105:147-152 (discussion 153), 1993 58. Havel M, Grabenwoger F, Schneider J, et al: Aprotinin does not decrease early graft patency after coronary artery bypass grafting despite reducing postoperative bleeding and use of donated blood. J Thorac Cardiovasc Surg 107:807-810, 1994 59. Bohrer H, Fleischer F, Lang J, et al: Early formation of thrombi on pulmonary artery catheters in cardiac surgical patients receiving high-dose aprotinin [see comments]. J Cardiothorac Anesth 4:222-225, 1990

108 60. BaubiUier E, Cherqui D, Dominique C, et al: A fatal thrombotic complication during liver transplantation after aprotinin administration. Transplantation 57:1664-1666, 1994 61. Diefenbach C, Abel M, Limpers B, et al: Fatal anaphylactic shock after aprotinin reexposure in cardiac surgery. Anesth Analg 80:830-831, 1995 62. Bayo M, Ferrandiz M, Casas Jl, et al: [Allergic reaction following the administration of aprotinin in mitral valve replacement (letter)] Reaccion alergica postadministracion de aprotinina en el recambio valvular mitral. Rev Esp Anestesiol Reanim 41:123-124, 1994 63. Cottineau C, Moreau X, Drouet M, et al: [Anaphylactic shock during the use of high doses of aprotinin in cardiac surgery] Choc anaphylactique lors de l'utilisation de l'apro-

WEISSMAN AND WILLIAMS tinine a fortes doses en chirurgie cardiaque. Ann Fr Anesth Reanim 12:590-593, 1993 64~ Schulze K, Graeter T, Schaps D, et al: Severe anaphylactic shock due to repeated application of aprotinin in patients following intrathoracic aortic replacement. Eur J Cardiothorac Surg 7:495-496, 1993 64a. Kon MF, Masumo H, Nakajima S, et al: Anaphylactic reaction to aprotinin following topical use of biological tissue sealant. Jpn J Anesthesiol 43:1601-1610, 1994 65. Tatar H, Cicek S, Demirkilic U, et al: Topical use of aprotinin in open heart operations. Ann Thorac Surg 55:659661, 1993 66. O'Regan DJ, Giannopoulos N, Mediratta N, et al: Topical aprotinin in cardiac operations. Ann Thorac Surg 58: 778-781, 1994