OBJECTIVE To assess pharmacokinetics of tranexamic acid (TXA) in dogs and assess antifibrinolytic properties of TXA in canine blood by use of a thromboelastography-based in vitro model of hyperfibrinolysis. ANIMALS 6 healthy adult dogs. PROCEDURES Dogs received each of 4 TXA treatments (10 mg/kg, IV; 20 mg/kg, IV; approx 15 mg/kg, PO; and approx 20 mg/kg, PO) in a randomized crossover-design study. Blood samples were collected at baseline (time 0; immediately prior to drug administration) and predetermined time points afterward for pharmacokinetic analysis and pharmacodynamic (thromboelastography) analysis by use of an in vitro hyperfibrinolysis model. RESULTS Maximum amplitude (MA [representing maximum clot strength]) significantly increased from baseline at all time points for all treatments. The MA was lower at 360 minutes for the 10-mg/kg IV treatment than for other treatments. Percentage of clot lysis 30 minutes after MA was detected was significantly decreased from baseline at all time points for all treatments; at 360 minutes, this value was higher for the 10-mg/kg IV treatment than for other treatments and higher for the 20-mg/kg IV treatment than for the 20-mg/kg PO treatment. Maximum plasma TXA concentrations were dose dependent. At 20 mg/kg, IV, plasma TXA concentrations briefly exceeded concentrations suggested for complete inhibition of fibrinolysis. Oral drug administration resulted in a later peak antifibrinolytic effect than did IV administration. CONCLUSIONS AND CLINICAL RELEVANCE Administration of TXA improved clot strength and decreased fibrinolysis in blood samples from healthy dogs in an in vitro hyperfibrinolysis model. Further research is needed to determine clinical effects of TXA in dogs with hyperfibrinolysis.

OBJECTIVE To determine pharmacodynamic and pharmacokinetic profiles of aminocaproic acid (ACA) by use of a thromboelastography (TEG)-based in vitro model of hyperfibrinolysis and high-performance liquid chromatography–mass spectrometry. ANIMALS 5 healthy adult dogs. PROCEDURES A single dose of injectable ACA (20, 50, or 100 mg/kg) or an ACA tablet (approximately 100 mg/kg) was administered orally. Blood samples were collected at 0, 15, 30, 45, 60, 90, 120, and 240 minutes after ACA administration for pharmacokinetic analysis. Samples were obtained at 0, 60, and 240 minutes for pharmacodynamic analysis by use of a TEG model of hyperfibrinolysis. RESULTS No adverse effects were detected. In the hyperfibrinolysis model, after all doses, a significantly higher TEG maximum amplitude (clot strength), compared with baseline, was detected at 60 and 240 minutes. Additionally, the percentage of fibrinolysis was reduced from the baseline value at 60 and 240 minutes, with the greatest reduction at 60 minutes. At 240 minutes, there was significantly less fibrinolysis for the 100 mg/kg dose than the 20 mg/kg dose. Maximum plasma ACA concentration was dose dependent. There was no significant difference in pharmacokinetic parameters between 100 mg/kg formulations. CONCLUSIONS AND CLINICAL RELEVANCE In an in vitro model of hyperfibrinolysis, ACA inhibited fibrinolysis at all doses tested. At 240 minutes after administration, the 100 mg/kg dose inhibited fibrinolysis more effectively than did the 20 mg/kg dose. Thus, ACA may be useful for in vivo prevention of fibrinolysis in dogs. IMPACT FOR HUMAN MEDICINE These data may improve research models of hyperfibrinolytic diseases.

Protein C content and plasminogen activity were measured in plasma from 100 horses with signs of colic. Data were analyzed by grouping horses 4 ways. Each horse was allotted to 1 of 2 outcome groups (survivors and nonsurvivors), 1 of 3 broad-category diagnosis groups (inflammatory disorders, strangulating obstructions, and all other gastrointestinal disorders), and 1 of 2 clinical management groups (medical and surgical). In a fourth grouping, all horses (although numbers of horses included in each subgroup were small) were assigned either to specific diagnostic groups that had high expectation for activated hemostasis (intestinal ischemia, endotoxemia, jugular thrombosis, peritoneal adhesions, and laminitis) or to a control group, in which active hemostasis was unlikely. Within 2 to 24 hours after admission, nonsurvivors developed lower protein C content than did survivors. Protein C content and plasminogen activity became low during hospitalization in horses with strangulating obstructions and in horses having surgery. The results from the grouping by specific diagnosis must be considered pilot data because the numbers of horses in each subgroup were small. Although not statistically significant, trends were noticed in protein C and plasminogen: (1) horses with intestinal ischemia and endotoxemia developed low protein C content and plasminogen activity, (2) protein C content became low in horses that developed peritoneal adhesions or laminitis, and (3) plasminogen activity became low in horses that developed jugular thrombosis. Low protein C content or low plasminogen activity, or both, may be useful as predictors for outcome and for these specific complications of equine colic. Protein C content and plasminogen activity were often normal at admission, but decreased by 2 to 24 hours; therefore, the hemostatic alterations appear to be an effect, rather than a cause of the gastrointestinal disorders. A return to normal values over several days may signify clinical improvement.

The balance of coagulation and fibrinolysis was studied in 15 horses during the prodromal stages of acute laminitis induced by carbohydrate overload. Progression of the disease was stopped 12 to 24 hours before the expected onset of lameness in trial 1 (8 horses) and at the onset of lameness in trial 2 (7 horses). The end points in each trial were identified by specific changes in blood pressures (trial 1) and by changes in pulse, rectal temperature, and arterial pressure (trial 2) that were anticipated on the basis of original description of the experimental model. Blood samples for hemostasis evaluation were collected before and after carbohydrate overload in trial 1 and after carbohydrate overload in trial 2. Significant changes were not detected in platelet count, mean platelet volume, prothrombin time, activated partial thromboplastin time, fibrinogen concentration, plasminogen concentration, alpha-2-antiplasmin, antithrombin III, protein C, thromboxane B2, or fibrin(ogen) degradation product concentration. We concluded that an imbalance in coagulation and fibrinolysis is not pathogenic in the onset of experimentally induced equine acute laminitis. Because several test methods used to evaluate hemostasis in these horses were new, reference values for 34 healthy adult horses were established.

Changes in clotting time (CT) and fibrinolytic activity (FA) were evaluated in 6 mature, female horses during exercise. Two trials were performed on consecutive days, using a randomized crossover design. Each mare was assigned to either an exercise trial or a control trial on the first day, and to the alternate trial 24 hours later. Mares exercised for 20 minutes on a treadmill at an elevation of 2 degrees and a velocity of 5 m/s. Venous blood samples were collected immediately before exercise, at 4, 8, 12, 16, and 20 minutes during exercise, and 15 minutes after cessation of exercise. Blood was placed into plain glass tubes for determination of CT, and into chilled, citrated tubes for determination of FA, plasminogen/plasmin complex activity (PLG), one-stage prothrombin time (OSPT), activated partial thromboplastin time (APTT), and antithrombin-III (AT-III) activity. There were significant differences (P < 0.05) between the control and exercise groups for CT, FA, and PLG. During exercise, clotting time decreased from 21.5 +/- 1.6 minutes to 9.9 +/- 1.6 minutes (mean +/- SD; P < 0.05), without significant changes in OSPT, APTT, or AT-III. Fibrinolytic activity and PLG increased (P < 0.05) during exercise. Changes in CT, FA, and PLG were significant at 4 minutes of exercise, remained altered until the end of exercise, and returned to baseline values by 15 minutes of recovery. Clotting time, OSPT, APTT, FA, AT-III, and PLG did not change (P > 0.05) during control trials.

Fetal and neonatal lamb hemostasis were studied from the 60th day of pregnancy to birth. Platelet counts and blood coagulation, as assessed by tests such as recalcification time and thromboelastography, were similar in fetuses, neonates, and adult sheep. The values of coagulation factors were low, ie, vitamin K-dependent Factors II, VII, IX, and X remained unchanged (30 and 40% of adult reference values) until the last 10 days of gestation, and then increased until birth (40 to 60%). Values of fibrinogen and Factor V followed a similar pattern, although their activities became identical to adult values at birth. Also, we measured values of protein C and antithrombin III, which are synthesized by the liver. The importance of hepatic failure and fetal vitamin K deficiency were discussed. Factors VIII and XII activities increased gradually during pregnancy to reach adult values at birth. Fetal fibrinolytic activity increased. This could not be explained by the values or tissue-type plasminogen activator (it was not detectable) or by the presence of its fast-acting inhibitor, whose concentration did not decrease.

OBJECTIVE To determine effects of oral administration of Yunnan Baiyao on platelet activation, coagulation, and fibrinolysis in healthy horses. ANIMALS 12 healthy adult horses. PROCEDURES In a randomized blinded crossover study that included a 4-week washout period between treatments, horses were orally administered a paste containing Yunnan Baiyao (15 mg/kg) or placebo at 12-hour intervals for 3 days. Blood samples were collected before start of treatment (time 0) and at 24 and 72 hours for a CBC, measurement of fibrinogen concentration, coagulation screening tests, and a panel of assays to assess platelet activation (including ADP- and collagen-induced aggregation and closure times, flow-cytometric variables of platelet-leukocyte aggregates, platelet membrane P-selectin and phosphatidylserine expression, and microparticle release), von Willebrand factor (vWF) concentration, and cofactor activity. In addition, thrombelastography was used to evaluate fibrin formation in tissue factor–activated whole blood and plasma and to assess tissue plasminogen activator–induced plasma fibrinolysis. For each treatment, values obtained before and 72 hours after start of administration were compared by use of Wilcoxon signed rank tests. RESULTS Yunnan Baiyao treatment had no significant effect on any hemostatic variable, compared with results for the placebo treatment. CONCLUSIONS AND CLINICAL RELEVANCE Administration of Yunnan Baiyao at a dosage typically used in clinical practice had no effect on in vitro measures of platelet or vWF function and no enhancement of fibrin-clot formation or stability. Any hemostatic actions of Yunnan Baiyao may require higher dosages or result from cell-surface interactions at sites of vascular and tissue injury not examined in this study.

Objective—To optimize the overall hemostasis potential (OHP) assay for use with canine platelet-poor plasma and determine reference intervals in healthy dogs. Animals—40 healthy dogs. Procedures—Blood was collected from the dogs into citrated tubes, and platlet-poor plasma was obtained. The OHP assay and standard coagulation assays (prothrombin time, activated partial thromboplastin time, and fibrinogen concentration) were performed for each sample. The OHP assay outputs were tested for correlations with results of the standard coagulation assays, age, and sex. Results—Modifications to the published methodology for the OHP assay were required for use with canine plasma, with less coagulation activator (thrombin) and more fibrinolysis activator (tissue plasminogen activator) than used with human plasma. Male dogs had a higher OHP than did females. High fibrinogen concentrations were associated with increases in maximum optical density, OHP, and overall coagulation potential, and reduced prothrombin time was associated with increases in maximum optical density, overall coagulation potential, OHP, and maximum slope. Conclusions and Clinical Relevance—Results supported the use of the OHP assay as an accessible, cost-effective global coagulation assay. Further research is required to determine its clinical application as an alternative to thromboelastography or thrombin generation assays.

Cats with cardiomyopathy, especially dilated cardiomyopathy associated with taurine deficiency, often develop systemic thrombi. To investigate the relation of taurine deficiency to formation and persistence of thrombi, cats were made taurine-deficient by consumption of a casein-based taurine-deficient diet, then were evaluated for anticoagulant and pro-fibrinolytic activities and platelet function. The cats served as their own controls in the taurine-replete state; then, values were compared for the taurine-deficient state. Plasma (P < 0.01), blood (P < 0.05), and platelet (P < 0.05) taurine concentrations were decreased markedly after cats consumed the taurine-deficient diet for 6 weeks, compared with baseline concentrations before diet. Compared with the taurine-replete state, taurine deficiency induced significantly (P < 0.05) increased mean antithrombin III activity, no significant change in plasminogen and fibrinolytic activities, and similar clot retraction/lysis test results. Decreased (P < 0.01) adenosine diphosphate (ADP)-induced platelet aggregation and [14C]serotonin release, and slightly increased (P < 0.05) collagen-induced platelet [14C]serotonin release, but unchanged collagen-induced platelet aggregation were observed in taurine-deficient cats, compared with taurine-replete cats. Changes in antithrombin III activity most likely reflected hepatocellular acute-phase reaction, which indicates that taurine deficiency may induce a stress-responsive state. Results of platelet function testing indicate that taurine may modulate platelet responsiveness to physiologic agonists, but not in a consistent manner. That platelets from the taurine-deficient cats had decreased responsiveness to ADP, but increased responsiveness to collagen is surprising, because irreversible aggregation is mediated by release of granule-associated ADP after sufficient initial stimulus. All cats had normal clot retraction in dilute blood, which indicated adequate platelet numbers and function; however, clots failed to lyse in vitro. To the authors knowledge, this observation, at present, lacks adequate explanation. Development of marked taurine deficiency and altered in vitro results of anticoagulant activities and some platelet function tests did not result in clinical manifestations in our cats. Results of our study do not conclusively document a pathophysiologic role of taurine depletion in the formation or persistence of thrombi.

Plasma and peritoneal fluid samples were collected before and after surgery from 6 horses undergoing a ventral midline exploratory laparotomy and from 6 anesthetized control horses. Coagulation/fibrinolytic components measured in the plasma and peritoneal fluid of these horses included the functional activity of antithrombin III, alpha-2 antiplasmin, plasminogen, and protein C, and the concentrations of fibrinogen and fibrin degradation products. Peritoneal fluid antithrombin III, fibrin degradation products, and plasminogen values were significantly increased after surgery (over time) in principal horses. Compared with control horses, postoperative peritoneal fluid from horses undergoing laparotomy had significantly increased antithrombin-III activity at 12 and 72 hours, alpha-2 antiplasmin activity at 24 hours, fibrin degradation product concentrations at 6, 12, 24, 72, 96, and 144 hours, plasminogen activity at 6, 12, 24, 48, 72, and 96 hours, and protein-C activity at 12, 24, 72, and 96 hours. There were no significant changes in the peritoneal fibrinogen concentration in principal horses. Plasma plasminogen activity was significantly decreased at 24 hours after surgery in principal horses, compared with controls. Changes were minimal in the remaining plasma coagulation/fibrinolytic components of horses undergoing laparotomy. Plasma and peritoneal fluid values of anesthetized control horses did not change.