Prevention of the formation of arterial thrombi using different antiplatelet drugs: experimental study in 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.

Consensus on the Rational Use of Antithrombotics in Veterinary Critical Care (CURATIVE): Domain 3-Defining antithrombotic protocols

OBJECTIVES

To systematically examine the evidence for use of a specific protocol (dose, frequency, route) of selected antithrombotic drugs, in comparisons to no therapy or to other antithrombotic therapies, to reduce the risk of complications or improve outcomes in dogs and cats at risk for thrombosis.

DESIGN

Standardized, systematic evaluation of the literature, categorization of relevant articles according to level of evidence (LOE) and quality (Good, Fair, or Poor), and development of consensus on conclusions via a Delphi-style survey for application of the concepts to clinical practice.

SETTINGS

Academic and referral veterinary medical centers.

RESULTS

Databases searched included Medline via PubMed and CAB abstracts. Eight different antithrombotic drugs were investigated using a standardized Patient, Intervention, Comparison, Outcome (PICO) question format both for dogs and cats, including aspirin, clopidogrel, warfarin, unfractionated heparin (UFH), dalteparin, enoxaparin, fondaparinux, and rivaroxaban, generating a total of 16 worksheets. Most studies identified were experimental controlled laboratory studies in companion animals (LOE 3) with only four randomized controlled clinical trials in companion animals (LOE 1).

CONCLUSIONS

Overall, evidence-based recommendations concerning specific protocols could not be formulated for most antithrombotic drugs evaluated, either because of the wide range of dosage reported (eg, aspirin in dogs) or the lack of evidence in the current literature. However, clopidogrel administration in dogs and cats at risk of arterial thrombosis, notably in cats at risk of cardiogenic thromboembolism, is supported by the literature, and specific protocols were recommended. Comparably, aspirin should not be used as a sole antithrombotic in cats with cardiomyopathy. Using the available safety profile information contained in the literature, the panel reached consensus on suggested dosage schemes for most antithrombotics. Significant knowledge gaps were highlighted, which will hopefully drive novel research.

Juvenile nephropathy in two related Pembroke Welsh corgi puppies

Juvenile nephropathy has been documented in many breeds. Two related Pembroke Welsh corgi puppies presented at three and five months of age, respectively, for evaluation of lethargy, diarrhoea, poor body condition, polyuria and proteinuria. Based upon the clinical presentation, urinalysis and serum biochemistry, chronic renal failure was diagnosed. Renal histopathology was consistent with juvenile nephropathy, revealing lesions similar to the juvenile renal disease of dobermann dogs. To the authors' knowledge, this is the first report of juvenile nephropathy in related Pembroke Welsh corgi dogs. Familial nephropathy should now be considered as a differential diagnosis in cases of young Pembroke Welsh corgi dogs presenting with clinical signs indicating renal failure.

Antithrombotic effect of TA-993, a novel 1,5-benzothiazepine derivative, in conscious rats

Since reported experimental models of thrombosis are not suitable for comparison of several drugs by oral administration, we developed a convenient model for this purpose by applying direct current through an intravascular electrode. In conscious rats, which were implanted with anodal electrodes in the abdominal aorta on the day before the experiment, application of 200 microA of direct current induced the formation of a platelet-rich thrombus around the intravascular electrode. Using this model, we studied the antithrombotic effect of the novel antiplatelet agent TA-993, (-)-cis-3-acetoxy-5-(2-(dimethylamino)ethyl)-2,3-dihydro-8-methyl-2-(4- methylphenyl)-1,5-benzothiazepin-4(5H)-one maleate, and compared its effect with other antiplatelet agents. TA-993 at doses of 30 mg/kg, p.o. or more by single administration or at doses of 10 mg/kg or more by repeated administration dose-dependently suppressed the thrombus formation. Aspirin (10 mg/kg, p.o. or more), cilostazol (100 mg/kg, p.o.) and ticlopidine (30 mg/kg, p.o. or more) also suppressed the thrombus formation by single administration. These results suggest that TA-993 has a comparable antithrombotic effect with other antiplatelet agents, and thus it is a possible remedy for thrombotic and embolic diseases.

Application of new coatings for vascular grafts based on polyacrylic systems with antiaggregating activity

A study has been made of the behaviour of knitted and woven Dacron mesh used in the preparation of vascular grafts when coated with either a layer of poly(2-hydroxyethyl methacrylate) or co-polymers of 2-hydroxyethyl methacrylate with 5, 10 or 20 wt% of an acrylic derivative of salicylic acid, 2-methacryloyloxybenzoic acid. In vitro studies were carried out to quantify the loss of polymer under flow conditions, and ex vivo studies were done in dogs to quantify the deposition of 111In-oxine-labelled platelets. The treated materials showed a lesser deposition of platelet thrombi when compared with the control group.

Prevention of arterial thrombosis by a monoclonal antibody against the 100 to 109 amino acid sequence stretch of the beta-subunit of the human platelet fibrinogen receptor: a comparative study with low dose aspirin

OBJECTIVES

The aim of this study was to compare, in dogs, the antithrombotic activity of aspirin and the murine monoclonal antibody P37, which inhibits platelet aggregation and fibrinogen binding to activated platelets.

BACKGROUND

The antithrombotic activity of P37 has been somewhat predictable, given its in vitro platelet antiaggregating activity and localization at or very near the fibrinogen binding site in the platelet fibrinogen receptor, the glycoprotein IIb/IIIa or integrin alpha IIb-beta 3.

METHODS

The monoclonal antibody P37 of the immunogamma-globulin-1 isotype was prepared according to previously described immunization and fusion protocols and screening assays. To compare its antiaggregating capacity with that of aspirin, experimental thrombosis was induced in all dogs by means of direct current applied to the carotid artery. Autologous platelets had previously been labeled with indium-111 oxine. The dogs were assigned to three groups: group I (n = 18) was the control group; group II (n = 12) was treated orally with 5 mg of aspirin/kg body weight per day for 7 days before induction of thrombosis, and group III (n = 10) was treated intravenously with a single dose of P37 (0.8 mg/kg).

RESULTS

The indium-111 oxine activity deposited in the thrombi was 12.94 +/- 12.83% (mean +/- SD) in group I, 3.55 +/- 2.99% in group II and 0.03 +/- 0.03% in group III. The differences between groups were always statistically significant (p < 0.05).

CONCLUSIONS

We conclude that a single dose (0.8 mg/kg) of P37 in a canine model of arterial thrombosis is approximately 100 times more efficient than the administration of aspirin (5 mg/kg per day) in preventing platelet deposition during thrombus formation.

Prevention of thrombus formation on biomaterials exposed to blood using different antiplatelet drugs: experimental study in dogs

An ex vivo shunt, established in dogs between both femoral arteries and right atrium, has been used to quantify the platelet deposition on six prosthetic materials used in the construction of cardiovascular prostheses: highly porous knitted Dacron (intervascular HP 800, 1400 mL/cm2/min/120 mm Hg), low-porosity woven Dacron (intervascular LP 200, 200 mL/cm2/min/120 mm Hg), double velour knitted Dacron, Avcothane 51 elastomere, and the mesothelial and epipericardial surfaces of bovine pericardium. In the search for a method to prevent platelet thrombi formation on these materials, we studied four groups of dogs: group 1 (control), group 2 (5 mg/kg body weight (BW)/day acetylsalicylic acid), group 3 (20 mg/kg BW/day acetylsalicylic acid), and group 4 (5 mg/kg BW/day acetylsalicylic acid plus 5 mg/kg BW/day dipyridamole). Platelets were labeled with 111In-oxine. The least thrombogenic material was Avcothane 51 elastomere. The only effective treatment for reduction of platelet deposition on the six materials was 5 mg/kg BW/day of acetylsalicylic acid. The dose used in group 3 only decreased the deposition of platelets on three of the six materials studied. The treatment employed in group 4 did not significantly reduce the deposition of platelets on any of the materials when compared with the control group.