Perioperative drugs that impair coagulation

My notes flag four drugs or groups: nonaspirin NSAIDs, warfarin, aspirin and clopidogrel. Their mechanisms differ, so a drug's plasma half-life does not tell us when haemostasis has recovered.

The original and second-edition Table 7.5 give these recall intervals: nonaspirin NSAIDs, at least 24 hours; warfarin, 3–7 days; aspirin and clopidogrel, 7–10 days. These are conditional book cues, not validated stop rules for every dog or cat. The table weighs bleeding risk against thromboembolism. The exact drug, formulation, species, regimen, procedure and patient matter. Some veterinary NSAID products are labelled for perioperative use.

Aspirin irreversibly inhibits platelet COX-1. This reduces thromboxane A2 production and can impair platelet function. The effect on exposed platelets lasts beyond aspirin's time in plasma. Recovery depends on platelet turnover. Other NSAIDs differ in COX selectivity and usually inhibit COX reversibly; their platelet effects vary with the drug and the test used.

Warfarin inhibits vitamin K epoxide reductase. This limits vitamin K recycling and production of functional factors II, VII, IX and X. It mainly affects secondary haemostasis. Thrombocytopathia means impaired platelet function.

Clopidogrel is a prodrug activated by hepatic metabolism. Its active metabolite irreversibly blocks ADP signalling at P2Y12. This prevents ADP-driven activation of platelet integrin αIIbβ3, fibrinogen binding and sustained aggregation. The original 1–2-day onset cue is regimen- and species-dependent. It is not the same as a withdrawal interval or time to maximal effect. Arterial thromboprophylaxis includes secondary prevention of cardiogenic arterial thromboembolism in cats.

The other original thrombocytopathia cues are colloids, hepatic disease and disseminated intravascular coagulation (DIC). These can affect several parts of haemostasis; effects are context-dependent.

References

Johnston/Tobias, 2nd ed., Ch. 7; Hogan 2004/2015; Blois 2010; Mullins 2012.