Apixaban-Related Acute Interstitial Nephritis: A Rare Adverse Effect

Introduction: Apixaban is widely prescribed for the prevention of stroke and systemic embolism in atrial fibrillation and the management of venous thromboembolism. Its favorable efficacy and safety profile has escalated its use. However, emerging evidence suggests that apixaban may be associated with adverse renal effects. Here we report a case of apixaban related acute interstitial nephritis. Case Description: A 62-year-old female with atrial fibrillation, hypertension, hyperlipidemia initially presented to hospital after elevated creatinine on outpatient labs. Patient denied any symptoms apart from fatigue and continued to make urine. She reported the initiation of apixaban 1 month prior to admission. She reported no proton pump inhibitor or antibiotic use. Patient was afebrile and normotensive on admission. She appeared euvolemic and had no rashes or skin changes. Initial laboratory findings were notable for sCr 4.5 mg/dL, serum sodium 137 mmol/L, serum potassium 3.7 mmol/L, serum bicarbonate 20 mmol/L, blood urea nitrogen 50 mg/dL, white blood cell count 8.8 x109/L with 5.3% eosinophils on differential. Urinalysis was noted to have positive leukocyte esterase, 30 mg/dL protein, 50 red blood cells per high power field, and 26 white blood cells per high power field with few eosinophils. Urine protein creatinine ratio with 1.69 g/g protein. Urine culture was found to have no growth. Serologic work up was unremarkable. Serum creatinine peaked at 4.6 mg/dL. A renal biopsy was completed and notable for diffuse interstitial infiltrate enriched in eosinophils and mononuclear inflammatory cells. Immunofluorescence and electron microscopy were unremarkable. A diagnosis of acute interstitial nephritis was made. Apixaban was discontinued and transitioned to warfarin. Patient was started on prednisone 1 mg/kg (80 mg daily). Serum creatinine improved to 3.5 mg/dL at the time of discharge. Patient was continued on steroid taper. Two weeks after discharge, sCr had improved to 1.54 mg/dL. Discussion: This case report highlights the importance of vigilance regarding apixaban-induced AIN, particularly as the use of apixaban continues to rise. While AIN remains a relatively rare side effect of apixaban therapy, clinicians should maintain a high index of suspicion when evaluating patients with unexplained renal dysfunction and be prepared to promptly diagnose and manage this potentially reversible condition.