title: Life-threatening retroperitoneal bleeding due to warfarin-drug interactions.
abstract: Warfarin-drug interactioions, which can result in life-threatening bleeding, are preventable. A 53-year-old man was admitted to hospital with exacerbation of chronic obstructive airways disease, cor pulmonale, pneumonia, deep vein thrombosis and acute pulmonary embolism. His pulmonary thromboemobolism was initially treated by low-molecular-weight-heparin and heparin. After a loading dose of 5 mg for 2 days, warfarin was given in a daily dose of 2 mg. On the fifth day of warfarin therapy, the last dose of Enoxaparin was given in the morning. He had a fall in the bathroom with blunt injury to the right flank. He complained of right thigh numbness and increasing pain and swelling over his right flank and abdomen. A tender mass was noted over the right flank. His Hb level dropped to 9.7 g/dl. His INR increased from 2.46 to 3.49-3.71 one day later. On further questioning, he admitted self applications of 20 g of Analgesic balm (50% methyl salicylate) over his right calf for 3 days. CT scan showed a large right retroperitoneal haematoma and right iliacus intramuscular haematoma. Warfarin was withheld. He was given fresh frozen plasma, packed cells and vitamin K(1). Inferior vena cava filter was inserted. The haematomas were resolving. He was subsequently discharged to convalescence hospital for continuation of anticoagulant therapy and close monitoring. Significant usage of topical methyl salicylate ointment can potentiate the anticoagulant effect of warfarin. The over-anticoagulation and the presence of platelet dysfunction increase the risk of severe bleeding, which can be provoked by trauma.
authors.affiliation: Division of Clinical Pharmacology, Department of Medicine and Therapeutics, Faculty of Medicine, The Chinese University of Hong Kong, Prince of Wales Hospital, New Territories, Hong Kong. tykchan@cuhk.edu.hk
authors.forename: Thomas Y K
authors.initials: TY
authors.lastname: Chan
mesh_terms: D000925:Anticoagulants / Q000009:adverse effects*; D004347:Drug Interactions; D006470:Hemorrhage / Q000139:chemically induced*; D006801:Humans; D019934:International Normalized Ratio; D008297:Male; D008875:Middle Aged; D010314:Partial Thromboplastin Time; D012187:Retroperitoneal Space; D012459:Salicylates / Q000009:adverse effects*; D014859:Warfarin / Q000009:adverse effects*
chemical_list: D000925:Anticoagulants; D012459:Salicylates; D014859:Warfarin; C033069:methyl salicylate