Abstract Title Drug Induced ANCA Vasculitis with Long-standing Tolerance to Hydralazine. Background Anti-neutrophil cytoplasmic antibodies (ANCA) associated vasculitis has a varied presentation and positive ANCA antibodies are commonly found in granulomatosis with polyangiitis, microscopic polyangiitis (MPA), renal-limited vasculitis, and drug-induced vasculitis. Specific ANCA antibodies, anti-protease 3 (PR3) and myeloperoxidase (MPO), can help differentiate between the various vasculitides with MPO-ANCA most closely associated with MPA, renal limited, and drug induced. Kidney biopsies most frequently demonstrate necrotizing crescentic glomerulonephritis. Symptoms vary depending on the organ system involved but consistently involve signs of systemic inflammation and end organ damage. Case Presentation This case presents a 67-year-old male with history of chronic obstructive pulmonary disease (COPD), chronic kidney disease stage IV (CKD IV), and hypertension presenting with newfound hematuria, acute respiratory failure, and altered mentation. He was found to be hypertensive and ultimately required intubation for airway protection. On review of home medications, antihypertensive regimen includes hydralazine, carvedilol, and nifedipine. Urinalysis was significant for significant hematuria and proteinuria. Lab work was significant for elevated creatinine, blood urea nitrogen, and respiratory acidosis. Rheumatologic work up revealed positive titers for antinuclear antibodies 1:640, ANCA, myeloperoxidase antibodies at 35 U/mL, and weakly positive anti-histone antibodies at 1.3 units. Work up negative for C3 abnormalities, anti-glomerular basement membrane antibodies, and anti-PR3 titers. Renal biopsy showed pauci-immune necrotizing crescentic glomerulonephritis. A presumptive diagnosis of drug-induced ANCA-associated MPA was made and methylprednisolone was started for 3 days. The patient was transitioned to high dose prednisone with appropriate taper until outpatient follow up for reevaluation. The patient also started on a two part rituximab infusion occurring 14 days apart. The patient’s renal and pulmonary function responded well to the steroid and rituximab treatment. The patient was successfully stabilized and discharged with appropriate prophylaxis and scheduled appointments for the outpatient Rituximab infusion and nephrology follow up. Discussion ANCA-associated vasculitis has a wide spectrum of symptom presentations. Thorough medication reconciliation and work up for any new acute kidney injury should include investigation into autoimmune pathologies when occurring with widespread organ involvement. Drug -induced ANCA vasculitis can present in a patient even after years of taking high risk medications, and as such previous tolerance should not exclude a new drug reaction. Furthermore, the proper coordination of inpatient services with outpatient therapy is required to promote optimum patient outcomes.