Treatment Outcomes of Mycobacterium Avium Complex Pulmonary Disease With a Two Drug Regimen Using Macrolide and Ethambutol

Abstract Background: Limited data exist on the treatment outcomes of a two-drug regimen of macrolide and ethambutol in patients with Mycobacterium avium complex pulmonary disease (MAC-PD). In this study, we aimed to evaluate the microbiological responses, antibiotic resistance rates, and recurrence rates in MAC-PD patients who received macrolides and ethambutol treatment for more than 12 monthsMethods: In total, 108 patients with MAC-PD who completed at least 12 months of treatment with macrolides and ethambutol were included in this outcome analysis. Results: The median overall treatment duration for 108 patients was 13.2 months (interquartile range [IQR] 12.1-14.6 months). A total of 72 (67%) patients achieved culture conversion and microbiological cure, with a median time to culture conversion of 1.7 months (IQR 1.2-4.0 months). A clinical cure was observed in 11 patients; thus, 83 (77%) patients demonstrated a favorable overall response. In the multivariate analysis models adjusted for important clinical variables, no clinical factors were significantly associated with culture conversion. Among patients who failed to achieve culture conversion, macrolide resistance developed in 2 of 18 patients (11%) who had both pre- and post-treatment isolates available. In two other patients who failed culture conversion, the minimum inhibitory concentration for ethambutol in the post-treatment isolates increased to ≥ 8 μg/mL, which was considered resistant. Of the 72 patients who achieved a microbiological cure, 16 (22%) experienced recurrence during follow-up. Conclusions: The two-drug regimen of macrolides and ethambutol showed moderate efficacy in treating MAC-PD when used for > 12 months. However, macrolide resistance occurred in some refractory cases, and recurrence was noted even after successful treatment, highlighting the need for close follow-up.