Leukocytoclastic Vasculitis Associated with Coumarin Derivatives: A Case Report.

Coumarin derivatives, including warfarin and acenocoumarol, are widely used oral anticoagulants that inhibit vitamin K-dependent coagulation factors. They are commonly prescribed for the prophylaxis of thromboembolic disorders. Although effective, these agents are associated with many adverse drug reactions, which include hemorrhagic complications, warfarin-induced skin necrosis, hypersensitivity reactions, and, rarely, leukocytoclastic vasculitis (LCV). LCV is an immune-mediated small-vessel vasculitis characterised by palpable purpura, often triggered by drugs, infections, or autoimmune conditions. Here, we present the case of a 53-year-old female with a history of rheumatic heart disease and mechanical mitral valve replacement who developed LCV after 5 years on acenocoumarol. The reaction persisted despite adjunct therapy and worsened upon switching to warfarin, suggesting possible cross-reactivity between these coumarin derivatives. Ultimately, transitioning to apixaban led to the complete resolution of symptoms. This case underscores the importance of early recognition of drug-induced vasculitis and highlights the need for individualised anticoagulation strategies in patients with hypersensitivity reactions.