The Duke MG Patient Registry III. Comparative Effectiveness of Azathioprine and Mycophenolate Mofetil in Generalized...

Azathioprine (AZA) and mycophenolate mofetil (MMF) are the most commonly used non-steroidal immunosuppressants in patients with generalized myasthenia gravis (gMG) in North America but their relative effectiveness among disease subgroups is not known. We reviewed data in the Duke MG Clinic Registry to compare the effectiveness of AZA and MMF in subgroups of patients with gMG.

This is a retrospective comparative effectiveness study of patients with acetylcholine receptor positive gMG receiving recommended doses of AZA or MMF for at least 90 days. Treatment goal (TG) was achieving MGFA Post-Intervention Status Minimal Manifestations. Time-to-event analysis, inverse probability of treatment weighting, and Cox proportional hazards (CPH) modeling were performed.

Among 320 cohort patients, 177 took AZA and 143 took MMF. TG was achieved by 66.1% taking AZA, median time 17.5 months, and 68.5% taking MMF, median time 10.5 months (p = 0.0004). Concomitant prednisone, taken by 2/3 of patients, increased the proportion of patients who reached TG with either drug (p < 0.0001). There was a positive correlation between disease duration at drug initiation and time to TG (Pearson r = 0.32, p = 2.3 × 10^-6).

Two-thirds of patients treated with AZA or MMF achieved TG after a median of 14 months. Patients taking MMF achieved TG sooner than those taking AZA, and concomitant prednisone increased the proportion of patients who achieved TG with either drug. Patients with shorter disease duration at drug initiation reached TG sooner with either drug. These results emphasize the value of concomitant prednisone and early immunosuppressive treatment of patients with gMG.