To the Editor:
We thank Dr. Park and colleagues1 for their interest in our letter2. They note another mechanism by which N-acetylcysteine might be useful as adjuvant therapy for patients with antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis. The studies that they cite3,4,5, along with those that we mentioned6,7, could be the basis to evaluate the hypothetical potential of high-dose acetylcysteine as an anti-vasculitic drug in randomized, placebo-controlled trials in humans. Meanwhile, the IFIGENIA trial (Idiopathic Pulmonary Fibrosis International Group Exploring N-Acetylcysteine I Annual study)8 revealed an interesting finding for patients treated with azathioprine that may have been overlooked. The dose of azathioprine in this trial was similar to doses used in patients with ANCA-associated vasculitis, and the bone marrow toxicity was significantly less frequent with acetylcysteine than with placebo. We believe that this lower hematologic toxicity justifies the study of high-dose acetylcysteine in patients with ANCA-associated vasculitis treated with azathioprine, regardless of a hypothetical anti-vasculitic action.