Biochemical comparison of seven commercially available prothrombin complex concentrates

Aims: A number of prothrombin complex concentrates (PCCs) are commercially available but they differ in terms of composition. We performed a series of studies to compare the biochemical properties of seven PCCs. Methods: The following products were investigated: Beriplex P/N, Octaplex, S‐TIM 4, PPSB Solvent Detergent, Uman Complex DI, Kaskadil and Cofact. Assays were performed to investigate levels of coagulation factors and their inhibitors, activated coagulation factors and heparin. The thrombin inhibitory capacity of each PCC was determined. Protein content was assessed using the Lowry method and sodium dodecyl sulphate–polyacrylamide gel electrophoresis. Results: The data indicated little difference between most of the products in their levels of factors II, VII, IX and X, with the exception of Uman Complex which had no detectable factor VII. In all cases, the measured levels of coagulation factors were broadly similar to those labelled. Beriplex P/N showed the greatest capacity for thrombin inhibition, a reflection of the observed high levels of the coagulation inhibitors protein C, protein S, protein Z, and small amounts of antithrombin III and heparin in this product. All of the PCCs tested were negative for activated coagulation factors. Purity (i.e. therapeutic protein as a percentage of total protein) was highest in Beriplex P/N, and the second purest product was Uman Complex. Conclusion: This in vitro study showed considerable differences between PCCs in terms of coagulation inhibitory capacity and purity.     

Substitution therapy with prothrombin complex concentrates in acquired coagulation disorders

Over the past 11 years two different plasma concentrates--Prothromblex500 (factor II, IX and X) and Prothromblex Total500 (factor II, VII, IX and X) have been used in the treatment of 246 patients with acquired coagulation disorders, in particular deficiencies of the prothrombin complex (factor II, VII, IX and X). Patients on oral anticoagulation or suffering from liver disease required substitute therapy for severe bleeding episodes, acute operations or invasive diagnostic procedures. Serial coagulation studies and analyses showed that both concentrates achieved adequate correlation of the abnormal coagulation, whereby better results were obtained in patients on oral anticoagulation than in patients with severe liver disease. All operations and diagnostic procedures were completed without haemorrhagic complications, whilst the patients admitted for a severe bleeding episode were rapidly brought under control. These plasma concentrates did not cause any side effects. No case of intravascular coagulation was observed following substitution therapy.     

Mechanism of the anticoagulant effect of warfarin as evaluated in rabbits by selective depression of individual procoagulant vitamin K-dependent clotting factors.

We have evaluated the contribution of depression of individual procoagulant vitamin K-dependent clotting factors to the ability of warfarin to protect rabbits against tissue factor-induced coagulation. Mean activities of individual procoagulant factors were determined, in assays with rabbit substrates, for a group of rabbits achieving a protective degree of anticoagulation with warfarin. Values were: factor VII, 12%; factor IX, 7%; factor X, 14%, and prothrombin, 13%. The effect upon tissue factor-induced coagulation of selective immunodepletion of each factor to a comparable level was then evaluated. Immunodepletion of plasma factor X or prothrombin, but not of factor VII or factor IX, protected otherwise normal rabbits against tissue factor-induced coagulation. Next, we determined the effect upon the protection in warfarin-treated rabbits of selectively restoring factor X or prothrombin before infusing tissue factor. When either factor was selectively restored, warfarin's protective effect was abolished. Moreover, selective restoration of prothrombin sensitized warfarin-treated rabbits to coagulation more severe than observed in nontreated control rabbits. One may extrapolate from these data that depression of both factor X and prothrombin are required for warfarin's clinical antithrombotic efficacy and that depression of plasma prothrombin is particularly important.     

Evaluation of vitamin K deficiency in children with acute and intractable diarrhea

The purposes of this study were to determine the frequency of vitamin K deficiency and to assess its effects on bleeding in patients with acute and intractable diarrhea. A total of 90 children with diarrhea and 30 healthy children (group C) were included in this study. Patients were divided into 2 groups, according to the duration of diarrhea. Complete blood count; prothrombin time (PT); activated prothrombin time (APTT); Factors II, VII, IX, and X; and protein C levels were studied in all patients. A total of 3 mg of vitamin K was administrated to patients with prolonged PT and/or APTT. Coagulation parameters were restudied 8 to 12 h after vitamin K was administered. Mean age, sex, weight, and breastfeeding percentage, as well as history of fever and vitamin K administration at birth, were similar in the 2 groups. The duration of antibiotic administration in group B (intractable diarrhea) was significantly longer than that in group A (acute diarrhea). Gastrointestinal (GI) bleeding was observed in 3 (4.9%) infants in group A and 6 (20.7%) in group B (P< .05). The duration of diarrhea was significantly longer in infants with GI bleeding. Intracranial bleeding occurred in 1 infant with intractable diarrhea. Prolonged PT levels were noted in groups A and B. Significant improvement in PT and APTT and an increase in coagulation factors were observed after vitamin K had been administered. Investigators in this study conclude that coagulation parameters can be improved by the administration of vitamin K to children with deranged PT and APTT and diarrheal illness.     

Isolated factor VII deficiency diagnosed after a life-threatening brain haemorrhage

A 65-year-old man was admitted to another hospital with a life-threatening brain haemorrhage, and laboratory examinations on admission revealed prolonged prothrombin time with normal activated partial thromboplastin time. To establish the cause of his abnormal coagulation, he was referred to our clinic. Neither the patient nor his family had any previous history of bleeding symptoms. His liver function was within normal limits but coagulation tests showed increased plasma activities of factors II, VIII, IX, X, with reduced activities of factors V and VII. The activity of factor VII was less than 2% but no inhibitor of factor VII was detected in the plasma. We concluded that the patient had a rare congenital isolated factor VII deficiency although he had not shown earlier bleeding problems, presumably because of compensation for the factor VII deficiency by enhanced activities of components of the extrinsic coagulation pathway, factors II, VIII, IX and X.     

Disappearance Rates of Coagulation Factors: Transfusion Studies in Factor-Deficient Patients

Data are presented describing the circulating levels of coagulation factors after transfusion of blood and plasma into patients with deficiencies of factors V, VII, VIII, IX, and X. The half-disappearance times of the factors were as follows: V, 16 hours; VII, 4 hours initially and 22.6 hours subsequently; VIII, 10.5 to 11 hours; IX, 4 hours initially, 39.5 hours subsequently; X, two components, the slower being 35 hours. All of the factors had an initial rapid disappearance with half-disappearance times of a few hours. For factors VII, IX, and X, a two-component logarithmic decrease was found. It is emphasized that, if these coagulation factors are proteins, they have half-disappearance times which are considerably shorter than those of most other plasma proteins. The therapeutic implication of this observation is discussed in relation to hemostatic levels and survival of the coagulation factors in banked blood.     

Blood coagulation in anhepatic pigs: effects of treatment with the AMC-bioartificial liver

Summary. The function of a newly devised bioartificial liver (AMC‐BAL) based on viable, freshly isolated porcine hepatocytes has been evaluated in anhepatic pigs. The aim of this study was to assess the contribution of BAL treatment on blood coagulation parameters. Pigs were anesthetized and a total hepatectomy was performed (n = 15). The infrahepatic caval vein and the portal vein were connected to the subdiaphragmatic caval vein using a three‐way prosthesis. Animals received standard intensive care (control, n= 5), treatment with an empty BAL (device control, n= 5) or with a cell‐loaded BAL (BAL‐treatment, n= 5) for a period of 24 h starting 24 h after hepatectomy. Coagulation parameters studied concerned prothrombin time (PT), platelet count, the procoagulant system (factors (F)II, FV, FVII, FVIII and fibrinogen), anticoagulant system (AT III), fibrinolytic system (t‐PA, PAI‐1) as well as markers of coagulation factor activation (TAT complexes, prothrombin fragment F1 + 2). FII, FV, FVII, AT III and fibrinogen rapidly decreased after total hepatectomy in pigs in accordance with the anhepatic state of the animals. FVIII levels were not influenced by the hepatectomy. A mild drop in platelet count was seen in all groups. Treatment of anhepatic pigs with the cell‐loaded BAL did not restore PT or clotting factor levels. TAT and F1 + 2 complexes, however, were significantly increased in this group. Levels of t‐PA and PAI‐1 were not influenced by cell‐loaded BAL treatment. Treatment of anhepatic pigs with the AMC‐BAL based on freshly isolated porcine hepatocytes does not result in an improved coagulation state due to extensive consumption of clotting factors. However, increased levels of TAT complexes and prothrombin fragments F1 + 2 during treatment of anhepatic pigs indicate synthesis and direct activation of coagulation factors, leading to thrombin generation. This demonstrates that this bioartificial liver is capable of synthesizing coagulation factors.     

A reappraisal of plasma, prothrombin complex concentrates, and recombinant factor VIIa in patient blood management

Plasma therapy and plasma products such as prothrombin complex concentrates (PCCs), and recombinant activated factor VII (rFVIIa) are used in the setting of massive or refractory hemorrhage. Their roles have evolved because of newly emerging options, variable availability, and heterogeneity in guidelines. These factors can be attributable to lack of evidence-based support for a defined role for plasma therapy, variability in coagulation factor content among PCCs, and uncertainty regarding safety and efficacy of rFVIIa in these settings. This review summarizes these issues and provides insight regarding use of these options in management of refractory or massive bleeding.     

Warfarin monitoring with viscoelastic haemostatic assays,thrombin generation,coagulation factors and correlations to Owren and Quick prothrombin time

The anticoagulant warfarin is commonly monitored with prothrombin time (PT). Viscoelastic haemostatic assays (VHA) are primarily used in situations of acute bleeding to guide haemostatic therapy. Much research has focused on VHA monitoring of new oral anticoagulants. However, many patients are still anticoagulated with warfarin and effect of warfarin anticoagulation on VHA is uncertain. The aim of this study was to assess warfarin anticoagulation on three different VHA and compare these findings with prothrombin time (PT), coagulation factor analyses and a thrombin generation assay (TGA). Citrated whole blood was drawn from 80 patients admitted for routine PT-INR Owren. VHA analysis with ROTEM (EXTEM, INTEM and FIBTEM), ReoRox (Fibscreen 1 and 2) and Sonoclot (gbACT+) was performed. Blood was also drawn for plasma analysis with PT (PT-INR Owren and PT Quick), TGA and analysis of factors I, II, VII, IX and X. Extrinsically activated VHA, including ROTEM EXTEM and FIBTEM Clotting Time (CT) and ReoRox Fibscreen1 and 2 clot onset time 1 correlated moderately with PT-INR Owren , with R 0.66–0.71. These four variables were likely to be prolonged above reference interval in patients with prolonged PT-INR Owren >1.2. Two patients with normal ROTEM CTs had Owren PT-INRs >1.5. Warfarin affects extrinsically activated VHA variables of initial clotting. The role of VHA for clinical decision-making in patients planned for invasive procedures, such as spinal/epidural anaesthesia needs further study. None of the recent guidelines on regional anaesthesia include VHA testing to define adequate haemostasis.     

450 million years of hemostasis

Summary.  In mammalian blood coagulation, five proteases (factor VII [FVII]; factor IX [FIX]; factor X [FX]; protein C [PC] and prothrombin [PT]) act with five cofactors (tissue factor [TF]; factor V [FV]; factor VIII [FVIII]; thrombomodulin and protein S) to control the generation of fibrin. Biochemical evidence, molecular cloning data and comparative sequence analysis support the existence of all components of this network in all jawed vertebrates, and strongly suggest that it evolved before the divergence of teleosts over 430 million years ago. Phylogenetic analysis of the amino acid sequences of the Gla–EGF1–EGF2–SP domain serine proteases (FVII, FIX, FX, PC) and the A domain-containing cofactors (FV and FVIII) strongly supports the evolution of the blood coagulation network through two rounds of gene duplication, and supports the hypothesis that vertebrate evolution benefited from two global genome duplications. The jawless vertebrates (hagfish and lamprey) that diverged over 450 million years ago have a blood coagulation network involving TF, PT and fibrinogen. Preliminary evidence indicates that they may have a smaller complement of Gla–EGF1–EGF2–SP domain proteins, suggesting the existence of a 'primitive' coagulation system in jawless vertebrates.     

Potentially catastrophic bleeding disorders. Approach to diagnosis and management

Clinical and laboratory evaluation of severe bleeding can detect the presence of an intrinsic or acquired coagulation disorder. The three most common inherited coagulation disorders are factor VIII deficiency (hemophilia A), factor IX deficiency (hemophilia B), and von Willebrand's disease. Vitamin K deficiency, liver disease, and disseminated intravascular coagulation are the most common acquired disorders. A thorough clinical history is crucial to diagnosis. Screening tests that measure prothrombin time, partial thromboplastin time, thrombin time, and platelet count permit initial classification and guide selection of more specific tests. Results can then be used to determine appropriate therapy.     

Problems of anticoagulation with warfarin in hyperthyroidism

From clinical observation it would appear that hyperthyroid patients are particularly sensitive to the anticoagulant effects of warfarin. A study was made of clotting factors prothrombin (II), VII, procoagulant VIII (VIIIC), IX and X and of prothrombin ratio (PTR) and partial thromboplastin time with kaolin (PTT-K). These parameters and warfarin levels were measured before and following a single dose of warfarin given to five patients when hyperthyroid and again when euthyroid. Hyperthyroidism was associated with lower activity of factor II and a shorter PTT-K. Warfarin produced a greater fall in factors II and VII and a greater increase in PTR and PTT-K in the hyperthyroid state than in the euthyroid state. The enhanced response to warfarin in hyperthyroidism was, however, relatively greater for the PTR than for the PTT-K. In order to produce adequate protection against intravascular thrombosis by a suitable prolongation of the PTT-K, it may be necessary in hyperthyroid patients to extend the PTR beyond the normal therapeutic range.     

Thrombin generation: phenotypic quantitation

Summary.  An individual's ability to generate thrombin following tissue factor stimulus was evaluated in 13 healthy male donors in a 6-month study. Thrombin generation in whole blood collected by phlebotomy, contact pathway suppressed by the presence of 100 µg mL⁻¹ corn trypsin inhibitor, was initiated by the addition of 5 p m tissue factor/10 n m phospholipid. Reactions were quenched at 20 min by the addition of an ethylenediaminetetraacetic acid (EDTA), benzamidine, FPRck cocktail. Thrombin generation was determined by an ELISA for thrombin–antithrombin III (TAT) complex formation. Results showed that the levels of TAT observed varied from 245 to 775 n m . Thrombin production was consistent within each individual, CVi = 11.6%, but varied significantly within the group, CVg = 25.2%, and correlated inversely with an individual's clotting time ( r  = − 0.54, P  = 0.07). No correlations were individually observed between TAT and C-reactive protein, antithrombin III, factors II, V, VII, VIII, IX and X, fibrinogen and prothrombin time. However, computer simulations, which integrated each individual's coagulation factor levels using the Speed Rx method (Hockin et al. , J Biol Chem 2002; 277: 18322), predicted maximum active thrombin levels (ranging from calculated values of 220–500 n m ) consistent with the empirically determined values. Overall, these data suggest that thrombin generated in whole blood exclusively by tissue factor stimulation can be used as an integrative phenotypic marker to determine an individual's response to a tissue factor challenge.     

The interaction between platelets and factor VII/VIIa.

Blood coagulation normally occurs when factor VII interacts with its specific cellular receptor, tissue factor, which is exposed when a blood vessel is severed. The factor VII/tissue factor complex then initiates a cascade of proteolytic reactions involving factors IX, X, prothrombin and fibrinogen, culminating in the formation of a fibrin clot. The role of platelets in the initiation phase of blood coagulation is still unclear. It has been postulated that platelets bind activated factor VIIa independently of tissue factor, and that this interaction forms the basis of the usefulness of high-dose recombinant factor VIIa in treating hemophiliacs with inhibitory antibodies, and other thrombocytopenia-like syndromes. In this review, we will examine the evidence for and against such an hypothesis, as well as discuss an alternative mechanism for the efficacy of high-dose factor VIIa in treating hemophilic patients with inhibitors.     

Cutaneous and systemic effects of varying doses of brown recluse spider venom in a rabbit model.

OBJECTIVE: To ascertain whether a dose response exists between the dose of brown recluse spider venom (BRSV) and the cutaneous and coagulation effects in a rabbit model. Cutaneous necrosis is a serious complication of brown recluse spider envenomation (spider bite with venom). Disseminated intravascular coagulation (DIC) is a dreaded complication of brown recluse envenomation in humans. New Zealand white (NZW) rabbits have proved to be a model for the study of therapeutic regimens to prevent skin necrosis after spider bites. We studied the venom's effects on the skin and the coagulation mechanism in this rabbit model to determine if a clear dose-response relationship could be established. Establishment of a dose-response relationship is an important first step in determining if the NZW rabbit is a suitable model to study both cutaneous and systemic effects of the venom. DESIGN: Thirty-six NZW rabbits were divided into three groups. One group received a saline injection, and the other two groups received a 4.0 microg or a 10.0 microg dose of purified BRSV intradermally into the skin on the dorsum of the back. METHODS: Blood was collected at baseline, 24, 48, and 72 hours. Tissue specimens were obtained after seven days during the animal necropsy and gross and microscopic pathology examination was conducted to assess tissue damage. Measurements included complete blood count (CBC); platelets; PT; activated partial thromboplastin time (APTT); fibrinogen (clottable, immunological); coagulation factors II, V, VII, VIII, IX, X, XI, XII; anti-thrombin (AT); alpha-2 antiplasmin (AP); Protein C (PC); mixing studies; lupus anticoagulant screening; plasminogen; thrombin-antithrombin; fibrin degradation products (FDP); d-dimer; and thrombin time. RESULTS: Gross pathology results were consistent with previous studies that used higher doses of BRSV. The WBC and platelet counts decreased at 24 hours in the two groups receiving the BRSV (p < 0.05). BRSV produced a dose related prolongation in the APTT (p < 0.05). Levels of fibrinogen as well as factors V, VII, VIII, IX, X, AT, and AP (p < 0.05) were increased in response to the BRSV. Protein C decreased at 24 hours (p < 0.05) and remained low in other time points. Mixing studies corrected the prolonged APTTs to normal ranges. Factor IIXI and XII showed no significant alteration in response to the BRSV. CONCLUSIONS: In the model, both the size and depth of the eschar were dose-related. We also observed a dose related elevation in the APTT that corrected with mixing studies. The dose-response relationship suggests direct interference by a component of the venom, rather than an idiosyncratic response. We did not detect a deficiency of commonly measured coagulation factors or evidence of a lupus anticoagulant. Protein C demonstrated a decrease. Although DIC did not occur in this rabbit model, a dose-related elevation in APTT was noted. The finding that the elevation corrected with mixing studies suggests that a plasma factor is essential in the coagulopathy associated with brown recluse envenomation. Further studies to identify this factor could shed light on human coagulopathy following envenomation.     

Plasma thrombopoietin level after liver transplantation: relationship to cold ischemia time and coagulation parameters

Objective: To determine the relation between thrombopoietin (Tpo) levels following orthotopic liver transplantation (OLT), cold ischemia time and postoperative peripheral blood platelet count and prothrombin activity.¶Design: Prospective clinical study.¶Setting: Intensive care unit.¶Patients: Fourteen patients with uncomplicated postoperative course after OLT.¶Measurements and results: Plasma Tpo, as quantified by enzyme immunoassay, rose significantly from 194.9 ± 45.7 pg/ml on day 1 after OLT to a peak value of 500.7 ± 94.1 pg/ml on day 5 while platelet count was below normal values. Then the platelet count increased and reached normal values while Tpo decreased to normal. The rise of Tpo levels was associated with normalization of prothrombin time but peak Tpo concentrations were in inverse correlation with cold ischemia times.¶Conclusion: The extent of production of Tpo in the liver graft following OLT is affected by cold ischemia time. This observation may be applicable in the prevention of bleeding complications associated with postoperative thrombocytopenia.     

Vitamin K-induced modification of coagulation phenotype in VKORC1 homozygous deficiency

Summary.  Background:  Combined vitamin K-dependent clotting factor (VKCF) deficiency type 2 (VKCFD2) is a rare bleeding disorder caused by mutated vitamin K 2,3-epoxide reductase complex subunit 1 (VKORC1) gene. Methods and results:  An Italian patient with moderate to severe bleeding tendency was genotyped, and found to be homozygous for the unique VKORC1 mutation (Arg98Trp) so far detected in VKCFD2. The activity levels of VKCFs were differentially reduced, and inversely related to the previously estimated affinity of procoagulant factor propeptides for the γ-carboxylase. The normal (factor IX) or reduced antigen levels (other VKCFs) produced a gradient in specific activities. Vitamin K supplementations resulted in reproducible, fast and sustained normalization of PT and APTT. At 24 h the activity/antigen ratios of VKCFs were close to normal, and activity levels were completely (factor VII and IX), virtually (prothrombin, factor X and protein C) or partially (protein S) restored. Thrombin generation assays showed a markedly shortened lag time. The time to peak observed at low tissue factor concentration, potentially mimicking the physiological trigger and able to highlight the effect of reduced protein S levels, was shorter than that in pooled normal plasma. At 72 h the thrombin generation times were normal, and the decrease in activity of procoagulant VKCFs was inversely related to their half-life in plasma. The improved coagulation phenotype permitted the uneventful clinical course after invasive diagnostic procedures. Conclusions:  Modification of coagulation phenotypes in VKCFD2 after vitamin K supplementation was clinically beneficial, and provided valuable patterns of factor specific biosynthesis, half-life and decay.     

Utilization of catecholic functionality in natural safrole and eugenol to synthesize mussel-inspired polymers

Naturally occurring safrole I upon epoxidation gave safrole oxide II, which underwent ring opening polymerization using a Lewis acid initiator/catalyst comprising of triphenylmethylphosphonium bromide/triisobutylaluminum to afford new polyether III in excellent yields. Epoxy monomer II and allyl glycidyl ether IV in various proportions have been randomly copolymerized to obtain copolymer V. A mechanism has been proposed for the polymerization reaction involving chain transfer to the monomers. A strategy has been developed for the deprotection of the methylene acetal of V using Pb(OAc)₄ whereby one of the methylene protons is replaced with a labile OAc group to give VI. The pendant allyl groups in VI have been elaborated via a thiol–ene reaction using cysteamine hydrochloride and thioglycolic acid to obtain cationic VII and anionic VIII polymers, both containing a mussel-inspired Dopa-based catechol moiety. During aqueous work up, the protecting group containing OAc was deprotected under mild conditions. Cationic VII and anionic VIII were also obtained via an alternate route using epoxide IX derived from 3,4-bis[tert-butyldimethylsilyloxy]allylbenzene. Monomer IX was homo- as well as copolymerized with IV using Lewis acid initiator/catalyst system to obtain homopolymer X and copolymer X1. Copolymer XI was then elaborated using a thiol–ene reaction followed by F⁻ catalysed silyl deprotection to obtain mussel inspired polymers VII and VIII, which by virtue of having charges of opposite algebraic signs were used to form their coacervate.

Naturally occurring safrole I upon epoxidation gave safrole oxide II, which underwent polymerization using a Lewis acid initiator/catalyst of triphenylmethylphosphonium bromide/triisobutylaluminum to afford new polyether III in excellent yields.     

Factor deficiencies in venom‐induced consumption coagulopathy resulting from Australian elapid envenomation: Australian Snakebite Project (ASP‐10)

Summary. Background: Limited information exists on the dynamics of hemostasis in patients with venom‐induced consumption coagulopathy (VICC) from snake envenomation. Objective: The aim of the present study was to investigate specific factor deficiencies and their time course in Australasian elapid envenomation. Methods: We measured coagulation parameters and factor concentrations in patients recruited to the Australian Snakebite Project, an observational cohort study. There were 112 patients with complete VICC, defined as an international normalized ratio (INR) > 3, and 18 with partial VICC. Serial citrated plasma samples were collected from 0.5 to 60 h post‐bite. INR, activated partial thromboplastin time (aPTT), coagulation factors (F)I, II, V, VII, VIII, IX, X, von Willebrand factor antigen (VWF:Ag) and D‐dimer concentrations were measured. Results: Complete VICC was characterized by near/total depletion of fibrinogen, FV and FVIII, with an INR and aPTT that exceeded the upper limits of detection, within 2 h of snakebite. Prothrombin levels never fell below 60% of normal, suggesting that the toxins were rapidly eliminated or inactivated and re‐synthesis of clotting factors occurred irrespective of antivenom. Partial VICC caused limited depletion of fibrinogen and FV, and almost complete consumption of FVIII. Onset of VICC was more rapid with brown snake (Pseudonaja spp.) venom, which contains a group C prothrombin activator toxin, compared with the tiger snake group, which contains a group D prothrombin activator toxin and requires human FVa formation. Resolution of VICC occurred within 24–36 h irrespective of snake type. Conclusions: These results suggest that Australasian elapid prothrombin activators have a potent but short duration of action. Antivenom is unlikely to be administered in time to prevent VICC.