Thrombin generation assay (TGA) is a sensitive method for the assessment of the global clotting potential of plasma. This kinetic assay can detect both hypocoagulable and hypercoagulable conditions: delayed or reduced thrombin generation leading to a prolonged clotting time, or induced thrombin activity, shifting the coagulation cascade toward thrombosis. The purpose of this study is to qualify the TGA in nonhuman primates (NHP) and rats for its use during nonclinical in vivo and in vitro studies. Blood was drawn from nonanesthetized animals, and platelet-poor plasma was obtained after double centrifugation; coefficients of variation were <10% for all derived parameters of thrombin generation assessed with 5 pM of tissue factor. Thrombin generation was evaluated in vitro in rat and NHP plasmas with ascending doses of unfractionated heparin (UFH), recombinant tissue factor, and anticoagulant compounds. Thrombin generation was decreased with UFH and anticoagulant compounds, but was increased in the presence of tissue factor, in a dose-dependent manner. In a rat model of inflammation, animals were administered a low dose of lipopolysaccharides. Thrombin generation measurements were decreased 3 hours post-LPS administration with a nadir at 24 hours, while thrombin–antithrombin complexes reached a peak at 8 hours, supporting an earlier production of thrombin. In conclusion, these data demonstrated that TGA can be performed in vitro for screening of compounds expected to have effects on coagulation cascade, and thrombin generation can be measured at interim time points during nonclinical in vivo studies in rats and NHP.

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A five-year-old neutered male Labrador Retriever was presented for recurring severe dyspnoeic episodes. Oral examination performed under sedation revealed a mass originating from the left arytenoid. CT highlighted a large perilaryngeal soft-tissue mass abutting the oesophagus, with a small intralaryngeal component. The mass created a narrowing of the laryngeal lumen and displaced the cranial cervical oesophagus dorsally and to the right. CT also highlighted a second smaller mass rostrally at the level of an oesophageal outpouching, narrowing the caudal aspect of the nasopharynx. The perilaryngeal mass was aspirated under ultrasound guidance. Cytology was suggestive of a tumour arising from skeletal muscle and a rhabdomyosarcoma was suspected. Due to poor prognosis, the patient was euthanased. Postmortem examination confirmed two masses affecting the cranial cervical oesophagus, one of which also invaded the perilaryngeal tissue. Histology and immunohistochemistry provided a final diagnosis of two concurrent oesophageal and perilaryngeal embryonal rhabdomyosarcomas.