212 J Med Assoc Thai Vol. 98 No. 2 2015 J Med Assoc Thai 2015; 98 (2): 212-6 Full text. e-Journal: http://www.jmatonline.com Case Report Correspondence to: Larpparisuth N, Division of Nephrology, Department of Medicine, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, 2 Prannok Road, Bangkok Noi, Bangkok 10700, Thailand Phone: +66-2-4198383, Fax: +66-2-4121762 E-mail: nl7569@yahoo.com Warfarin Related Nephropathy: The First Case Report in Thailand Nuttasith Larpparisuth MD*, Bunyarit Cheunsuchon MD**, Ratana Chawanasuntorapoj MD*, Somkiat Vasuvattakul MD*, Kriengsak Vareesangthip MD* * Division of Nephrology, Department of Medicine, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand ** Department of Pathology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand Warfarin is the most prescribed oral anticoagulant. Adverse renal effect from warfarin therapy are uncommon and Thailand is not acquainted. Warfarin-related nephropathy (WRN) is a newly recognized complication of warfarin treatment, especially in patients with chronic kidney disease. The authors hereby report a 56-year-old man who developed gross hematuria and severe acute kidney injury (AKI) necessitating hemodialysis, following supra-therapeutic INR level. Renal pathology revealed extensive intratubular obstruction with red blood cell casts. From the literature, there were only twelve case reports of WRN, which were confirmed by renal histopatology. Renal survival of this condition was unsatisfactory. However, our patient was dialysis-independent after vitamin K treatment and temporary warfarin discontinuation. To the best of our knowledge, this is the first case report of biopsy-proven WRN in Thailand. Keywords: Warfarin, Warfarin related nephropathy, Acute kidney injury, Intratubular hemorrhage, Gross hematuria, Anticoagulants Since an initial introduction to clinical practice in 1954, warfarin has become the most prescribed oral anticoagulant in the world. The most common side effect of warfarin is bleeding which is associated with supra-therapeutic dosage. Adverse renal effects from warfarin therapy are uncommon. Various renal complications of warfarin therapy have been reported, including pre-renal acute kidney injury (AKI) or ischemic acute tubular necrosis secondary to massive hemorrhage, atheroembolic renal disease, obstructive uropathy from renal hematoma (1) and acute interstitial nephritis with leukocytoclastic vasculitis (2) . In 2009, another distinct AKI syndrome associated with warfarin overdose was addressed. Brodsky SV et al reported nine patients who developed AKI resulting from intratubular red blood cell (RBC) casts obstruction (3) . Five of the nine patients experienced unfavorable renal outcome. This clinical entity was termed as “warfarin-related nephropathy” (WRN). Here, we report on a patient who developed gross hematuria and AKI necessitating hemodialysis following supra-therapeutic INR level. Renal pathology revealed intratubular obstruction with RBC casts without evidence of active glomerulonephritis. Case Report A 56-year-old man with well-controlled essential hypertension, presented with gross hematuria for 2 weeks. Two years ago, he developed Streptococcus suis endocarditis with severe mitral and aortic regurgitation. He underwent mitral valvuloplasty and aortic valve replacement with St. Jude prosthesis. Intravenous penicillin G sodium was given for four weeks. Warfarin had been started after the operation. At that time, he also experienced AKI with nephritis urine sediment and a low-complement C3 level. Cause of AKI was presumably endocarditis associated glomerulonephritis. Renal failure was resolved after completion of treatment. His blood urea nitrogen and serum creatinine at discharge were 17 and 1.4 mg/dl, respectively, which remained stable during the follow-up period. Urinalysis revealed no red blood cells (RBC) and urine protein per creatinine ratio (UPCR) was 1.1 g/g creatinine. He had excellent compliance and international normalized ratio (INR) was within acceptable range (range, 2.33 to 2.48 IU). Three weeks before the admission, he attended regular follow-up with a cardiovascular