Scientists probe mystery: does common antibiotic fight autoimmune disease by changing nasal bacteria?

This study aims to understand how a common antibiotic (trimethoprim-sulfamethoxazole) affects the community of bacteria and fungi in the nose of people with granulomatosis with polyangiitis (GPA), a rare autoimmune disease. Researchers will follow about 30 adult patients with GPA who are in remission, taking nasal swabs before, during, and after a 4-week course of the antibiotic to see how the nasal environment and immune markers change. The goal is to learn if the drug's benefit in preventing disease flare-ups comes from killing germs, reducing inflammation, or both.