Thromboembolic Therapies in Dogs and Cats: An Evidence-Based Approach

Retrospective Evaluation of Intravenous Enoxaparin Administration in Feline Arterial Thromboembolism

Simple Summary

Feline arterial thromboembolism is a painful disease characterized by acute ischemic necrosis of one or more limbs due to cardiac diseases, hyperthyroidism, or neoplasia. Among others, medical treatment consists of preventing new thrombus formation primarily using heparin products, such as enoxaparin. This retrospective study reports clinical data, regain of perfusion, short-term outcome, and complications of 36 affected cats treated with a novel intravenous enoxaparin protocol. Furthermore, we aimed to report monitoring and management of the intravenous enoxaparin treatment for this disease. In our population, visible hemorrhage was rare. The most common causes of death/euthanasia were cardiac instability, acute kidney injury, neurological abnormalities, and limb necrosis. The hospital discharge rate was 47% overall and was significantly different between single limb (83%) and dual limb (29%) thromboembolism. Our study supports the intravenous use of enoxaparin in combination with oral clopidogrel for cats with thromboembolism as an alternative treatment method.

Abstract

Induction of a hypocoagulable state is imperative in the treatment of feline arterial thromboembolism. Publications in human medicine report the use of enoxaparin intravenously in selected cases. The aim of our retrospective study was to report the regain of perfusion, short-term outcome, and complications of cats treated with a novel intravenous enoxaparin protocol (1 mg/kg bolus injection followed by 3 mg/kg/day continuous infusion) combined with oral clopidogrel administration. The secondary aim was to report the monitoring of enoxaparin with anti-Xa activity. There were 36 cats included. The probability of reaching limb reperfusion was significantly (p = 0.0148) higher with anti-Xa activity within or above the target range compared to results below the target range (19/21, 90% versus 11/20, 55%). The complications observed were acute kidney injury (15/36, 42%), hemorrhage (2/36, 6%), and neurological signs (6/36, 17%). The most common causes of death/euthanasia were cardiac instability, acute kidney injury, neurological abnormalities, and limb necrosis. The hospital discharge rate was 83% (10/12) for single limb and 29% (7/24) for dual limb thrombosis; the difference was significant (p = 0.0039). The median hospitalization time for the survivors was 119.5 (95–480) h. Our study supports the use of intravenous continuous rate infusion of enoxaparin in combination with oral clopidogrel for cats with aortic thromboembolism. We report similar discharge rates and lower hemorrhage rates than previously reported with thrombolytic treatment.

Evaluation of the Abdominal Aorta and External Iliac Arteries Using Three-Dimensional Time-of-Flight, Three Dimensional Electrocardiograph-Gated Fast Spin-Echo, and Contrast-Enhanced Magnetic Resonance Angiography in Clinically Healthy Cats

Arterial thromboembolism is associated with high morbidity and mortality rates in cats. Definitive diagnosis requires advanced imaging modalities, such as computed tomography angiography (CTA) and contrast-enhanced (CE) magnetic resonance angiography (MRA). However, CTA involves exposure to a large amount of ionized radiation, and CE-MRA can cause systemic nephrogenic fibrosis. Non-contrast-enhanced (NE) MRA can help accurately diagnose vascular lesions without such limitations. In this study, we evaluated the ability of NE-MRA using three-dimensional electrocardiograph-gated fast spin-echo (3D ECG-FSE) and 3D time-of-flight (3D TOF) imaging to visualize the aorta and external iliac arteries in clinically healthy cats and compared the results with those obtained using CE-MRA. All 11 cats underwent 3D ECG-FSE, 3D TOF, and CE-MRA sequences. Relative signal intensity (rSI) for quantitative image analysis and image quality scores (IQS) for qualitative image analysis were assessed; the rSI values based on the 3D TOF evaluations were significantly lower than those obtained using 3D ECG-FSE (aorta 3D TOF: 0.57 ± 0.06, aorta 3D ECG-FSE: 0.83 ± 0.06, P < 0.001; external iliac arteries 3D TOF: 0.45 ± 0.06, external iliac arteries 3D ECG-FSE:0.80 ± 0.05, P < 0.001) and similar to those obtained using CE-MRA (aorta: 0.58 ± 0.05, external iliac arteries: 0.57 ± 0.03). Moreover, IQS obtained using 3D TOF were significantly higher than those obtained using 3D ECG-FSE (aorta 3D TOF: 3.95 ± 0.15, aorta 3D ECG-FSE: 2.32 ± 0.60, P < 0.001; external iliac arteries 3D ECG-FSE: 3.98 ± 0.08, external iliac arteries 3D ECG-FSE: 2.23 ± 0.56, P < 0.001) and similar to those obtained using CE-MRA (aorta: 3.61 ± 0.41, external iliac arteries: 3.57 ± 0.41). Thus, 3D TOF is more suitable and produces consistent image quality for visualizing the aorta and external iliac arteries in clinically healthy cats and this will be of great help in the diagnosis of FATE.

Case Report: Non-traumatic Unilateral Forelimb Arterial Thrombosis Associated With Hyperadrenocorticism in a Dog

A 16-year-old spayed female Pomeranian dog was presented to the hospital with an acute onset of pain and non-weight-bearing lameness in the right forelimb. On physical examination, knuckling, coolness, pain, and cyanosis were observed in the affected forelimb. Peripheral blood glucose concentration and body surface temperature differed between the right and left forelimbs. Hypercoagulable thromboelastographic results and increased D-dimer levels were suggestive of thrombus. Accordingly, recombinant tissue plasminogen activator (rtPA) was administered intravenously. Prompt clinical improvements (including restored warmth of the affected limb) occurred, and rtPA was discontinued after two shots administered 2 h apart owing to concerns of bleeding side effects. The dog was discharged 6 days after admission, and outpatient treatment with clopidogrel was continued for the prevention of re-thrombosis. Following patient stabilization, further examinations for underlying diseases of hypercoagulability were conducted; hyperadrenocorticism (HAC) was diagnosed, and oral trilostane therapy was thus administered. Eight weeks later, the patient regained normal mobility. Finally, in the present canine patient with arterial thrombosis, thrombolysis with rtPA successfully improved clinical symptoms and the following administration of clopidogrel inhibited the formation of additional thrombus.

Dual therapy with clopidogrel and rivaroxaban in cats with thromboembolic disease

OBJECTIVES

Feline arterial thromboembolism (ATE), an often devastating outcome, was recently shown to affect 11.3% of cats with hypertrophic cardiomyopathy over 10 years. Current American College of Veterinary Internal Medicine guidelines recommend the use of clopidogrel in cats at risk for ATE, with addition of a factor Xa inhibitor in very high risk or post-ATE cases. To date, no studies have examined the safety or efficacy of this combined antithrombotic therapy. This retrospective case series aimed to assess the frequency and type of adverse events that occurred in cats prescribed dual clopidogrel and rivaroxaban therapy. Secondary aims were to evaluate indications for dual therapy and clinical outcome.

METHODS

The study included 32 cats prescribed clopidogrel (18.75 mg PO q24h) and rivaroxaban (2.5 mg PO q24h) on an outpatient basis over a 5-year period.

RESULTS

Cats were prescribed dual therapy for at least one of the following: ATE event (n = 18), presence of an intracardiac thrombi (n = 17) or presence of spontaneous echocardiographic contrast (SEC) (n = 16). Five cats experienced adverse effects that could be attributed to medications, a median of 13 days from initiation (epistaxis, hematemesis, hematochezia or hematuria). No cat required hospitalization as a result of these events. Median survival time from onset of therapy was 257 days (interquartile range [IQR] = 38-497) for all cats, 502 days (IQR = 171-663) for ATE cats, 725 days (IQR = 133-856) for cats with an ATE to two or more limbs and 301 days (IQR = 221-431) for cats with only one limb affected. Recurrence rate of ATE while on dual therapy was 16.7%; no cat newly developed an ATE while on dual therapy.

CONCLUSIONS AND RELEVANCE

Dual antithrombotic therapy with clopidogrel and rivaroxaban resulted in a low reported incidence of adverse events. Cats placed on dual therapy for an ATE event experienced a low rate of recurrence and effective thromboprophylaxis was achieved in cats with intracardiac thrombi or SEC.

The Use of Antithrombotics in Critical Illness

Hypercoagulable tendencies may develop in critically ill dogs and to a less known extent, cats. Although the use of antithrombotics is well-established in critically ill people, the indications and approach are far less well-known in dogs and cats. The goal of this article was to review the relevant CURATIVE guidelines, as well as other sources, and to provide recommendations for critically ill patients with directions for future investigation.

Outcome and treatments of dogs with aortic thrombosis: 100 cases (1997-2014)

Background

Aortic thrombosis (ATh) is an uncommon condition in dogs, with limited understanding of risks factors, outcomes, and treatments.

Objectives/Hypothesis

To describe potential risk factors, outcome, and treatments in dogs with ATh.

Animals

Client‐owned dogs with a diagnosis of ATh based on ultrasonographic or gross necropsy examination.

Method

Multicentric retrospective study from 2 academic institutions.

Results

One hundred dogs were identified. Anti‐thrombin diagnosis, 35/100 dogs were nonambulatory. The dogs were classified as acute (n = 27), chronic (n = 72), or unknown (n = 1). Fifty‐four dogs had at least one comorbidity thought to predispose to ATh, and 23 others had multiple comorbidities. The remaining 23 dogs with no obvious comorbidities were classified as cryptogenic. Concurrent illnesses potentially related to the development of ATh included protein‐losing nephropathy (PLN) (n = 32), neoplasia (n = 22), exogenous corticosteroid administration (n = 16), endocrine disease (n = 13), and infection (n = 9). Dogs with PLN had lower antithrombin activity than those without PLN (64% and 82%, respectively) (P = .04). Sixty‐five dogs were hospitalized with 41 subsequently discharged. Sixteen were treated as outpatient and 19 euthanized at admission. In‐hospital treatments varied, but included thrombolytics (n = 12), alone or in combination with thrombectomy (n = 9). Fifty‐seven dogs survived to discharge. Sixteen were alive at 180 days. Using regression analysis, ambulation status at the time of presentation was significantly correlated with survival‐to‐discharge (P < .001).

Conclusions/Clinical Importance

Dogs with ATh have a poor prognosis, with nonambulatory dogs at the time of presentation having worse outcome. Although the presence of comorbid conditions associated with hypercoagulability is common, an underlying cause for ATh was not always identified.

Abnormal platelet activity in dogs and cats - impact and measurement

Abnormal platelet activity can either lead to bleeding tendencies or inappropriate thrombus formation and can occur secondarily to a wide variety of disease processes, with a range of clinical consequences and severity. This article will discuss the pathophysiology of platelet function abnormalities and consider a logical diagnostic approach applicable to veterinary practice. Recent advances in platelet function testing will then be discussed, with regards to detection of platelet dysfunction and tailoring of pharmacological manipulation. Although many of these tests are still confined to research or academic institutions, techniques for indirectly assessing platelet function are starting to become more widely available. Although we still require further research to develop guidelines for the use of these tests in clinical decision-making, the recent advances in this field are an exciting step forward in being able to detect and manage platelet dysfunction in both primary care and referral practice.

Innovative application of an implantable venous access system in the portal vein: technique, results and complications in three dogs

Background

Vascular access port (VAP) systems are widely used in human medicine to provide long-term venous access. However, in veterinary medicine the use of VAP systems is not common practice and publications on their potential applications have been limited. A VAP system was used as part of an experimental study on liver regeneration and implanted in the canine portal vein to create direct access to the portal venous circulation of the liver. The aim of the present study is to describe the surgical technique, its use, and the complications of a VAP system in three research dogs.

Results

The VAP system was successfully used for the intraoperative measurement of portal blood pressure, the administration of cell suspensions, and the collection of portal venous blood samples. Long-term complications consisted of dislocation of the VAP system in one dog (2 months after implantation) and thrombus formation at the catheter tip in two dogs (3 months after implantation). Both complications prevented further use of the VAP but had no adverse clinical implications.

Conclusions

This pilot study suggests that the VAP system is an effective and safe technique to obtain long term access to the portal venous system in dogs. However, complications with port detachment and thrombosis may limit long term use of VAPs in the portal system of dogs.

American College of Veterinary Emergency and Critical Care (ACVECC) Consensus on the Rational Use of Antithrombotics in Veterinary Critical Care (CURATIVE) guidelines: Small animal

OBJECTIVES

To systematically review available evidence and establish guidelines related to the risk of developing thrombosis and the management of small animals with antithrombotics.

DESIGN

Standardized, systematic evaluation of the literature (identified by searching Medline via PubMed and CAB abstracts) was carried out in 5 domains (Defining populations at risk; Defining rational therapeutic use; Defining evidence-based protocols; Refining and monitoring antithrombotic therapies; and Discontinuing antithrombotic therapies). Evidence evaluation was carried out using Population, Intervention, Comparison, Outcome generated within each domain questions to address specific aims. This was followed by categorization of relevant articles according to level of evidence and quality (Good, Fair, or Poor). Synthesis of these data led to the development of a series of statements. Consensus on the final guidelines was achieved via Delphi-style surveys. Draft recommendations were presented at 2 international veterinary conferences and made available for community assessment, review, and comment prior to final revisions and publication.

SETTINGS

Academic and referral veterinary medical centers.

RESULTS

Over 500 studies were reviewed in detail. Worksheets from all 5 domains generated 59 statements with 83 guideline recommendations that were refined during 3 rounds of Delphi surveys. A high degree of consensus was reached across all guideline recommendations.

CONCLUSIONS

Overall, systematic evidence evaluations yielded more than 80 recommendations for the treatment of small animals with or at risk of developing thrombosis. Numerous significant knowledge gaps were highlighted by the evidence reviews undertaken, indicating the need for substantial additional research in this field.

Investigation into the causes of aspirin resistance in healthy dogs

Antiplatelet effects of acetylsalicylic acid (ASA, aspirin) may be poor in some individuals. Additionally, no method exists for predicting poor ASA response (resistance) in individual dogs. This study's main objective was to determine whether poor ASA response results from pharmacodynamic or pharmacokinetic causes. ASA concentrations causing 50% inhibition of platelet aggregation (in vitro IC50) were determined using whole blood collected from 21 drug-free healthy dogs to evaluate intrinsic sensitivity of platelets to ASA. Dogs were then administered ASA at 4 mg/kg once orally. Percent decrease in platelet aggregation from baseline, and plasma ASA and salicylic acid (SA) concentrations (expressed as AUC values) were measured for up to 3 hr. By 3 hr, 13/21 (62%) dogs showed >50% aggregation inhibition, while 8/21 (38%) dogs showed <50% inhibition. Aggregation inhibition values were negatively correlated with in vitro IC50 values (Rs = -0.49; p = 0.028) and positively correlated with ASA concentrations (Rs = 0.48; p = 0.03). Furthermore, ASA concentrations were strongly negatively correlated (Rs = -0.88; p < 0.001) with SA/ASA concentration ratios, an index of ASA metabolism to SA by esterase enzymes. Multiple linear regression analysis indicated that 59% (p < 0.001) of interindividual variability in aggregation inhibition was explained by in vitro IC50 values (29% of variability) and ASA concentrations (29% of variability). Consequently, poor in vivo ASA response in these dogs resulted from both pharmacodynamic (decreased platelet sensitivity) and pharmacokinetic (lower ASA concentrations) causes. Lower ASA concentrations may be explained by reduced bioavailability associated with higher esterase activities.

Establishment of reference ranges and evaluation of in vitro concentration-dependent platelet inhibition by acetylsalicylic acid for multiple electrode impedance aggregometry in healthy dogs

Acetylsalicylic acid (ASA, aspirin) is an antiplatelet medication used for prevention of thromboembolism. Effects of ASA appear to vary widely between dogs, but the underlying mechanisms are not understood. The Multiplate analyzer is a newer form of whole-blood impedance aggregometry recently validated for use in healthy dogs. A method utilizing this instrument to measure ASA effects on platelet function has not been established. The goals of this study were to establish reference ranges for the Multiplate in healthy dogs and secondly, to develop a technique to determine the in vitro concentration of ASA needed to cause 50% inhibition of platelet aggregation (IC50). Reference ranges established from 40 dogs at multiple test times for three agonists were consistent with previously published values. In vitro IC50 values were calculated using the sigmoid E_max model in 20 healthy dogs on two occasions to determine individual repeatability. Calculated in vitro IC50 demonstrated four ASA response groups: responder (n = 16), poor responder (n = 1), variable responder (n = 2), and nonresponder (n = 1). Multiplate within-assay variability was  <10% for area under the curve (AUC), and between-assay baseline AUC variability was  <15%. The described technique allowed for determination of an in vitro IC50 for ASA in dogs using a multiple electrode impedance aggregometer.

Bilateral Vertebral Venous Sinus Thrombosis Causing Cervical Spinal Cord Compression in a Dog

A 10-year-old male neutered mixed breed dog was evaluated for cervical hyperesthesia and tetraparesis. Magnetic resonance imaging of the brain and cervical spinal cord identified an extradural compressive lesion over the body of C2 caused by marked dilation of the vertebral venous sinuses. Following intravenous contrast administration both vertebral sinuses had heterogeneous contrast enhancement consistent with incomplete thrombi formation. An abdominal ultrasound also showed a distal aortic thrombus. A definitive cause for the thrombi formation was not identified, but the patient had several predisposing factors which may have contributed. The patient was treated with a combination of warfarin, clopidogrel, and enoxaparin as well as analgesics. Within 48 h of initiation of warfarin therapy, the tetraparesis and hyperesthesia were markedly improved. Repeat abdominal ultrasound 3 weeks after discharge showed reduction in size of aortic thrombus. Neurologic function remained normal for 6 weeks following initiation of treatment. Seventy-four days following initial diagnosis the patient rapidly declined and passed away at home. Necropsy was declined. This is the first report of vertebral venous sinus enlargement leading to spinal cord compression and tetraparesis in a dog. Additionally, warfarin in combination with clopidogrel and enoxaparin appeared to be a safe and effective treatment for the suspected thrombi reported in this case. Vertebral sinus enlargement secondary to thrombi should be considered as a differential diagnosis in patients presenting with tetraparesis and cervical hyperesthesia.

Heparinase-modified thromboelastography in cats

BACKGROUND

Evaluation of underlying hemostatic function is challenging when feline patients are receiving an anticoagulant medication. Discontinuing the anticoagulant to obtain accurate results for hemostatic testing may lead to thrombotic complications. The addition of heparinase to blood samples may mitigate the effects of exogenous heparin and allow hemostatic testing.

METHODS

Tissue factor (TF)-activated thromboelastography (TEG) was performed using citrated whole blood from 19 cats. Assays were performed using citrated whole blood, with and without addition of unfractionated heparin to a concentration of 0.2 U/mL. For each blood sample, TEG assays were performed using a standard cup and a heparinase-coated cup.

KEY FINDINGS

For TEG variables R, k, α-angle, and MA, mean values were not statistically different when citrated blood was used with standard or heparinase-coated cups. Heparinized blood assayed in standard cups displayed a significantly increased R and k, and significantly decreased α-angle and MA when compared to heparinized blood assayed in heparinase-coated cups. TEG variables for heparinized blood assayed in heparinase cups was not statistically different from those of the citrated whole blood without added heparin.

SIGNIFICANCE

Heparinase modified, TF-activated, TEG reverses heparin effects in feline-citrated blood.

Evaluation on antithrombotic effect of aspirin eugenol ester from the view of platelet aggregation, hemorheology, TXB2/6-keto-PGF1α and blood biochemistry in rat model

Background

Based on the prodrug principle, aspirin and eugenol, as starting precursors, were esterified to synthesize aspirin eugenol ester (AEE). The aim of the present study was to evaluate the antithrombotic effect of AEE in an animal disease model. In order to compare the therapeutic effects of AEE and its precursors, aspirin, eugenol and a combination of aspirin and eugenol were designed at the same molar quantities as the AEE medium dose in the control group.

Methods

After oral administration of AEE (dosed at 18, 36 and 72 mg/kg) for seven days, rats were treated with k-carrageenan to induce tail thrombosis. Following the same method, aspirin (20 mg/kg), eugenol (18 mg/kg) and 0.5 % CMC-Na (30 mg/kg) were administered as control drug. Different drug effects on platelet aggregation, hemorheology, TXB₂/6-keto-PGF_1α ratio and blood biochemistry were studied.

Results

AEE significantly inhibited ADP and AA-induced platelet aggregation in vivo. AEE also significantly reduced blood and plasma viscosity. Moreover, AEE down-regulated TXB₂ and up-regulated 6-keto-PGF_1α, normalizing the TXB₂/6-keto-PGF_1α ratio and blood biochemical profile. In comparison with aspirin and eugenol, AEE produced more positive therapeutic effects than its precursors under the same molar quantity.

Conclusion

It may be concluded that AEE was a good candidate for new antithrombotic and antiplatelet medicine. Additionally, this study may help to understand how AEE works on antithrombosis in different ways.

Consensus recommendations for standard therapy of glomerular disease in dogs

Standard therapy forms the basic foundation for care of dogs with glomerular disease, as it is herein recommended for use in all affected animals regardless of causation of the disease. Consensus recommendations target the evaluation and management of proteinuria, inhibition of the renin-angiotensin-aldosterone system, modification in dietary intake with special consideration for those nutrients with renal effects, diagnosis and treatment of systemic hypertension, and evaluation and management of body fluid volume status in dogs with glomerular disease.

49-month survival following caval venectomy without nephrectomy in a dog with a pheochromocytoma

An 11 yr old spayed female Labrador retriever was diagnosed with a right adrenal tumor. At surgery, adhesions to the right kidney were dissected, allowing the right kidney to be preserved. The tumor showed extensive invasion into the suprarenal vena cava. It was felt that thrombus removal via venotomy could not be performed. Instead, the vena cava was ligated caudal to the liver and cranial to the right renal vein. The neoplastic gland was then excised en bloc together with the portion of the invaded caudal vena cava. Hind limb edema had developed preoperatively and increased transiently in the first days postoperatively. The animal was discharged 6 days postoperatively with no other clinical disorders, and hind limb edema resolved over time. Histopathology identified a pheochromocytoma. The dog died 49 mo later. A neoplastic thrombus of the vena cava may require venotomy to allow thrombus removal. Occasionally, removal of the thrombus by venotomy may prove impossible. In such a situation, en bloc removal of the concerned portion of the vena cava may be performed with a good long-term outcome provided that gradual occlusion of the vena cava by the thrombus has allowed time for collateral circulation to develop.

Platelet signaling-a primer

OBJECTIVE

To review the receptors and signal transduction pathways involved in platelet plug formation and to highlight links between platelets, leukocytes, endothelium, and the coagulation system.

DATA SOURCES

Original studies, review articles, and book chapters in the human and veterinary medical fields.

DATA SYNTHESIS

Platelets express numerous surface receptors. Critical among these are glycoprotein VI, the glycoprotein Ib-IX-V complex, integrin α(IIb) β(3) , and the G-protein-coupled receptors for thrombin, ADP, and thromboxane. Activation of these receptors leads to various important functional events, in particular activation of the principal adhesion receptor α(IIb) β(3) . Integrin activation allows binding of ligands such as fibrinogen, mediating platelet-platelet interaction in the process of aggregation. Signals activated by these receptors also couple to 3 other important functional events, secretion of granule contents, change in cell shape through cytoskeletal rearrangement, and procoagulant membrane expression. These processes generate a stable thrombus to limit blood loss and promote restoration of endothelial integrity.

CONCLUSIONS

Improvements in our understanding of how platelets operate through their signaling networks are critical for diagnosis of unusual primary hemostatic disorders and for rational antithrombotic drug design.

Effect of pimobendan on the clinical outcome and survival of cats with non-taurine responsive dilated cardiomyopathy

This retrospective study was designed to assess the effect of pimobendan on the median survival time (MST) of cats with non-taurine responsive dilated cardiomyopathy (DCM). Thirty-two client-owned cats with a left ventricular internal dimension at end systole (LVIDs) >14 mm, a fractional shortening (FS) <28% and a lack of response to taurine therapy were included over a 9-year period (2001-2010). These cats were divided into pimobendan (n=16) and non-pimobendan (n=16) treatment groups. All cats received standard treatment with frusemide, taurine and benazepril or enalapril. Nine cats in the non-pimobendan group also received digoxin. The MST of the pimobendan group (49 days; range 1 to >502 days) was four times that of the non-pimobendan group (12 days; 1 to 244 days). The difference in survival between the two groups was statistically significant (P = 0.048). Hypothermia and FS <20% were associated with a poor prognosis. No adverse effects to pimobendan were noted.

Unilateral femoral arterial thrombosis in a dog with malignant mammary gland tumor: clinical and thermographic findings, and successful treatment with local intra-arterial administration of streptokinase

An 8-year-old intact female dog presented with a sudden onset of unilateral hindlimb paralysis of 3 days duration. Based on the history and results of physical, neurological, and histopathological examinations, and blood work, an arterial thrombosis was suspected as a complication of the hypercoagulability from a malignant mammary gland tumor. Thermography provided evidence of the unilateral femoral thrombus. Initially, thrombolysis with streptokinase administered by intravenous infusion was ineffective. Thereafter, the direct delivery of streptokinase to the site of thrombus was attempted. The approach was curative. These results suggest that thermography could describe the site of the arterial thrombus, and local intra-arterial administration of streptokinase may be an effective therapy for the canine arterial thrombosis complicated by malignant mammary gland tumor.

Lack of inhibitory effect of acetylsalicylic acid and meloxicam on whole blood platelet aggregation in cats

OBJECTIVE

To determine the effects of acetylsalicylic acid (ASA) and meloxicam on feline platelet aggregation and associated platelet thromboxane production and serotonin release.

DESIGN

Prospective interventional study.

SETTING

University research facility.

ANIMALS

Eight healthy male castrated domestic short hair cats from a research colony.

INTERVENTIONS

Oral medications were administered to 8 cats for 14 days in a randomized, placebo-controlled, crossover design. Treatment groups included: aspirin (ASA) (5 mg/kg q 48 h), meloxicam (0.05 mg/kg q 24 h), and placebo (0.5 mL of water q 24 h). Thromboxane assays (TXB(2) ) and whole blood (impedance) aggregometry (WBA) were performed on samples collected before drug administration, and on days 7, 15, and 17, using adenosine diphosphate (ADP; 10 μM) and collagen (5 μg/mL) as agonists for WBA. Serotonin release was assayed on postaggregation plasma. Oral mucosal bleeding time (OMBT) and complete blood cell counts were measured on days 0 and 15.

MEASUREMENTS AND MAIN RESULTS

Neither medication affected WBA at any time point. OMBT decreased in the ASA group relative to baseline. No differences were detected in WBA and OMBT baseline between any groups. No difference was detected in serotonin secretion at any time point. TXB(2) was significantly decreased in the ASA group at all times after initiation of treatment but no change was noted in the meloxicam or placebo groups.

CONCLUSIONS

At the doses studied, neither meloxicam nor ASA had an inhibitory effect on WBA or OMBT in cats. Thromboxane concentrations were significantly decreased with ASA treatment.

Pharmacokinetics of the low molecular weight heparin dalteparin in cats

Low molecular weight heparin (LMWH) is used as an anticoagulant in cats although only limited pharmacokinetic data are available in this species. The aim of the present study was to establish the pharmacokinetics of dalteparin in cats based on anti-FXa heparin activities. Groups of clinically healthy cats (six animals per treatment) received individual LMWH injections at three different doses intravenously (IV) (25, 50, 100 anti-factor Xa international units [IU anti-FXa]/kg) or subcutaneously (SC) (50, 100, 200 IU anti-FXa/kg). Blood samples were collected before and at various times after injection. Anti-FXa activity was measured with a chromogenic substrate test. Following IV injection, maximum plasma heparin activities (C(max)) were 0.67 ± 0.14, 1.44 ± 0.22 and 2.87 ± 0.38 IU anti-FXa/mL, respectively. The calculated mean half-life (t(½)) was between 39 and 57 min and was not significantly dose-dependent (P=0.139). The volume of distribution (35-39 mL/kg) was almost equivalent to the plasma volume. After SC injection, C(max) values of 0.41 ± 0.10, 0.86 ± 0.17 or 1.91 ± 0.16 IU anti-FXa/mL, respectively, were calculated at 91-110 min post-injection. The t(½) values were between 106 and 122 min and were not significantly influenced by dose (P=0.784). The bioavailability after SC injection was approximately 100%. The high bioavailability of the SC administered LMWH dalteparin in cats was consistent with other species and indicated predictable blood levels. However, the comparatively short t(½) may indicate the necessity of multiple daily injections, which should be verified in clinical trials.

Thromboembolic Conditions, Aetiology Diagnosis and Treatment in Dogs and Cats

In veterinary medicine, thrombo-embolism (TE) is an under-appreciated medical condition that requires immediate recognition. Since TE is multifactorial and its mode of presentation may vary, veterinarians face great difficulties in making a definitive diagnosis in a timely manner. In addition, most of the underlying conditions that give rise to TE are life-threatening and an aggressive diagnostic and therapeutic approach is required. Not only does the diagnosis and treatment of this condition require the collaboration of many specialties, the costs of therapy can be excessive with a high risk of recurrence. As such, owners have to be thoroughly informed before the therapy commences. While TE has been well-characterized in humans and is associated with significant morbidity and mortality, little information of similar quality is available in veterinary medicine. In addition, TE in animals is distinct from its human counterpart and we cannot simply adapt what is known from human clinical trials. With the promise of improvements in imaging modalities that improve our diagnostic capabilities, the window of opportunity to treat TE increases. This article focuses on aetiology, clinical presentation, diagnosis, and treatment of dogs and cats affected by TE.

Effects of prednisone alone or prednisone with ultralow-dose aspirin on the gastroduodenal mucosa of healthy dogs

BACKGROUND

The coadministration of prednisone and ultralow-dose aspirin has been recommended for the management of various diseases, but the safety of this combination in dogs has not been studied.

HYPOTHESES

The gastroduodenal lesions associated with prednisone and ultralow-dose aspirin administration will be similar to those caused by prednisone alone, but both treatments will result in more severe lesions than placebo.

ANIMALS

Eighteen healthy adult purpose-bred dogs.

METHODS

Randomized, blinded, placebo-controlled study of 3 treatment groups for 27 days: placebo, prednisone, and prednisone and aspirin. Gastroduodenoscopy was performed before and on days 5, 14, and 27 of treatment and mucosal lesions scores were assigned. Mucosal lesion scores were compared by a Kruskal-Wallis test. Clinical signs were compared by the Friedman's chi-square test (significance at P < .05).

RESULTS

There were no significant differences in the gastroduodenal lesion scores among groups, or within groups at any time during the study. Significantly more dog-days of diarrhea occurred in the prednisone and aspirin group during treatment, compared with baseline. No significant differences in clinical signs were found among any of the groups.

CONCLUSION

The concurrent use of prednisone and ultralow-dose aspirin did not increase the severity of gastroduodenal lesions compared with prednisone or placebo. Coadministration of prednisone and ultralow-dose aspirin increases the frequency of mild, self-limiting diarrhea in some dogs.