The availability of effective immunosuppressive medication has greatly improved survival for patients with antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) but also conveys increased infection risk. Infections are the leading cause of death in the year following diagnosis1 and the most common reason for hospitalization in AAV patients.2 To reduce these risks, multiple clinical practice guidelines, including those from KDIGO,3 recommend prophylaxis against Pneumocystis jiroveci pneumonia (PJP) with trimethoprim/sulfamethoxazole (TMP/SMX) for AAV patients receiving rituximab or cyclophosphamide.