A prospective evaluation of rivaroxaban on haemostatic parameters in apparently healthy dogs

Monitoring of Rivaroxaban Therapy in Hypercoagulable Dogs

BACKGROUND

Measurement of rivaroxaban efficacy using the rivaroxaban-specific anti-Xa assay (raXa) can be used for monitoring in veterinary medicine. Detection of rivaroxaban efficacy using other hemostatic tests would make monitoring timelier and more accessible.

OBJECTIVES

Compare results of raXa with prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen concentration, tissue factor (TF) and kaolin-activated thromboelastography (TEG), and thrombin generation (TG) in hypercoagulable dogs.

ANIMALS

Twelve client-owned dogs, diagnosed with hypercoagulability or thromboembolic disease, and prescribed rivaroxaban, were recruited from a tertiary referral hospital from 2020 to 2022.

METHODS

Prospective clinical trial. Jugular vein blood samples were collected before treatment, and 1 week and 1-3 months after initiation of rivaroxaban therapy. Hemostatic tests were performed at each visit (3 h after rivaroxaban dosing). TG curve parameters lag time, endogenous thrombin potential (ETP), peak, and time to peak (ttpeak) were assessed.

RESULTS

There was a significant linear relationship between raXa and PT (r2 = 0.74, p < 0.001), ETP (r2 = 0.83, p < 0.001), lag time (r2 = 0.87, p < 0.001), peak (r2 = 0.86, p < 0.001), and ttpeak (r2 = 0.86, p < 0.001). There was a weak linear relationship between raXa and kaolin-activated TEG parameter reaction time (R) (r2 = 0.49, p = 0.026). There was no significant relationship between raXa and aPTT, fibrinogen concentration and the remainder of the TEG variables (p > 0.05).

CONCLUSION AND CLINICAL IMPORTANCE

PT and TG correlated with raXa. PT performed at a reference laboratory appeared to be a convenient method to monitor a small cohort of dogs receiving rivaroxaban therapy.

Comparison of the pharmacokinetics and pharmacodynamics of apixaban and rivaroxaban in dogs

BACKGROUND

Comparative pharmacokinetics and pharmacodynamics (PK/PD) of apixaban and rivaroxaban have not been studied in dogs and the propensity of these drugs to cause hypercoagulability after discontinuation is unknown.

HYPOTHESIS

Compare the PK/PD of clinical dosing regimens of PO apixaban and rivaroxaban administered repeatedly to healthy dogs and assess the effect of abrupt drug discontinuation on coagulation.

ANIMALS

Six University-owned, purpose-bred, middle-aged, mixed-breed dogs (4 male, 2 female).

METHODS

Dogs were given apixaban or rivaroxaban PO at 0.5 mg/kg q12h for 7 days with a 14-day washout period between drugs. Plasma drug concentrations were quantitated, and anticoagulant effects were measured using clotting times, calibrated anti-Xa bioactivity assays, and measurements of thrombin generation. The potential for rebound hypercoagulability was assessed by measuring D-dimers, thrombin-antithrombin (TAT) complexes, and antithrombin activity after drug discontinuation.

RESULTS

Plasma drug concentrations and anti-Xa bioactivities were closely correlated for both drugs, but drug concentrations varied considerably among dogs, despite consistent dose regimens. Thrombin generation variables were significantly correlated with the anti-Xa bioactivity of both drugs and no significant differences in the effects of apixaban and rivaroxaban on thrombin generation were observed. Drug discontinuation had no effect on D-dimer concentrations. The concentration of TAT complexes decreased after apixaban discontinuation and did not change after rivaroxaban discontinuation.

CONCLUSIONS AND CLINICAL IMPORTANCE

Repeated PO administration of apixaban or rivaroxaban to healthy dogs produced comparable anticoagulant effects measured by inhibition of thrombin formation. Rebound hypercoagulability after drug discontinuation was not observed and weaning of these drugs in clinical patients might not be necessary.

Case report: Severe hepatopathy following rivaroxaban administration in a dog

Rivaroxaban, a specific factor Xa inhibitor and commonly utilized anticoagulant, has been known to cause hepatotoxicity and liver failure in humans. Although rivaroxaban is frequently used in veterinary medicine, hepatotoxicity has not been previously reported in dogs. The current case report describes a dog that developed severe hepatopathy following rivaroxaban administration for a large right pulmonary artery thrombus. An estimated 6-year-old spayed female mixed-breed dog developed anorexia and lethargy 9 days after rivaroxaban administration began. Subsequent labwork revealed severe hepatocellular hepatopathy, and rivaroxaban was discontinued. Additional diagnostics did not reveal an underlying etiology, although hepatic cytology could be consistent with a toxic injury. The hepatopathy and clinical signs improved after rivaroxaban was discontinued. The time to onset, type of hepatopathy, and time to resolution were all similar to those reported for human cases. This case provides precedence to advocate for improved and closer monitoring of dogs receiving factor Xa inhibitors. In cases of suspected hepatotoxicity with no other identifiable cause, a risk-benefit analysis should be performed, and discontinuation of rivaroxaban administration or alternative anticoagulant medications should be considered.

Clinical features and posttreatment monitoring of dogs administered rivaroxaban (2018-2020): 19 cases

OBJECTIVE

To describe a population of sick dogs administered rivaroxaban monitored with a rivaroxaban-calibrated anti-Xa activity assay (aXa).

DESIGN

Descriptive retrospective study.

SETTING

Two veterinary teaching hospitals.

ANIMALS

Client-owned dogs administered rivaroxaban and monitored with aXa from January 2018 to January 2020 were eligible for study.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Medical records were reviewed and 19 dogs with a variety of underlying disease processes were identified. Rivaroxaban was administered to 12 of 19 dogs (63%) with confirmed thrombosis, 4 of 19 dogs (21%) with a strong clinical suspicion of thrombosis, and in 3 of 19 dogs (16%) with no current evidence of thrombosis. The median rivaroxaban dose administered was 0.96 mg/kg/day (0.62-1.58 mg/kg/day), with 15 of 19 dogs (79%) receiving rivaroxaban once daily. Clopidogrel was concurrently administered to 11 of 19 dogs (58%). Complete or partial thrombus resolution was identified in 5 of 12 (42%) and 3 of 12 (25%) dogs, respectively. Rivaroxaban appeared safe, with only 1 of 19 dogs (5%), concurrently administered clopidogrel, developing evidence of mild hematuria. Posttreatment monitoring revealed that 8 of 19 dogs (42%) had aXa below the target (aXa range of 150-250 ng/ml associated with effective treatment and prevention of venous thrombosis in people). The remaining 3 to 19 dogs (16%) achieved this range, and 8 of 19 dogs (42%) exceeded the range. No significant relationship between the initial rivaroxaban dose administered and the corresponding aXa result was identified. There were also no significant differences in baseline clinicopathological variables in dogs in which aXa fell within or outside this range.

CONCLUSIONS

aXa was most commonly measured in dogs receiving rivaroxaban with confirmed or suspected thrombosis. Dogs in this study received a range of rivaroxaban dosages and attained variable aXa values that were not directly correlated with dosage.