ACUTE KIDNEY INJURY SECONDARY TO KIDNEY CRYSTALLIZATION ATTRIBUTABLE TO NELFINAVIR. Zaher Hamadeh, Tejinder S. Ahuja, Jeffrey Kopp. Jacobi Medical Center, New York, NY; University of Texas Medical Branch, Galveston, TX; National Institutes of Health, Bethesda, MD. Indinavir a Protease Inhibitor (PI) that can cause nephrolithiasis, crystalluria and acute kidney Injury (AKI). We are reporting a case of AKI and kidney crystallization induced by Nelfinavir another PI. A 72 years old African American male with history of HIV infection admitted with a creatinine of 3.2mg/dl (0.9mg/dl 4 months ago). His CD4 lymphocyte count is 753cells per cubic millimeter, viral load < 75 copies/ml and has been on the same highly active antiretroviral therapy (HAART) regimen including Nelfinavir for the last 2 years. He denied hematuria, back or flank pain. There was no history of urinary retention, nephrolithiasis or Nephrotoxins use. Labs showed no eosinophilia. Urinalysis showed bland urine sediment with no proteinuria. Renal ultrasound was unremarkable. Percutaneous kidney biopsy was performed and light microscopy showed tubules with intraluminal deposits and chronic tubulo-interstitial nephritis (see Fig); Electron Microscopy confirmed the amorphous crystals within the tubular lumina. Nelfinavir serum trough level was 3ug/ml at the upper normal (normal range of 1-3ug/ml). HPLC was done on a urine sample which detected Nelfinavir. A kidney tissue sample was sent for Mass Spectrometry which showed MW of the kidney crystals consistent with Nelfinavir free-base. HAART regimen was discontinued and creatinine level returned to 1.4mg/dl eight months later.