Chinese Herbal Medication Induces Interstitial Nephritis Treated with Infliximab Therapy and Monitored with Urinary Retinol-Binding Protein-to-Creatinine Ratio

Introduction: The mainstay of treatment for interstitial nephritis remains stopping the offending agent and glucocorticoid therapy. However, infliximab therapy has been shown as an effective treatment for immune checkpoint inhibitor induced interstitial nephritis. Here we describe a case of interstitial nephritis and oxalate nephropathy after Chinese herbal medication exposure that was treated with infliximab therapy and monitored with urinary retinol binding protein (RBP)/Crt ratio. Case Description: A 75-year-old male with pre-diabetes, hypertension, CKD stage II presented with 1-2 weeks of poor oral intake, decreased urine output and progressively worsening altered mental status. On initial work up, he had an acute kidney injury (serum creatinine 16.5 mg/dL) superimposed on CKD (baseline serum creatinine 1.4 mg/dL). The only new medication was Nhan Sam Tuyet Lien Truy Phong Hoan. His initial URBP/Crt ratio was elevated (57,925 mcg/g) along with his CRP level (9mg/dL). The patient’s kidney function did not improve, so he was initiated on temporary hemodialysis. A kidney biopsy was performed revealing acute on chronic active interstitial nephritis and intratubular calcium oxalate crystals. The patient started oral steroid treatment, showed clinical improvement, and was able to come off hemodialysis. However, he developed steroid induced psychosis and was initiated on infliximab therapy. After 2 doses of infliximab (5mg/kg IV), he had progressive improvement in his kidney function (serum creatinine 2.1 mg/dL), uRBP/Crt ratio (600mcg/g), and CRP level (<3 mg/dL). His steroids were tapered off in 3 weeks as a result. Discussion: Although infliximab is not the mainstay of treatment for interstitial nephritis, our patient achieved resolution of his acute kidney injury after 2 treatments. The uRBP/Crt ratio measurements correlated with the progressive improvement in the patient’s kidney function. This case highlights the utility of uRBP/Crt ratio in interstitial nephritis and showcases infliximab as an alternative, steroid-sparing, treatment for non-immune checkpoint inhibitor interstitial nephritis.