Serum Mycophenolic Acid Levels and Infection Risk in Myasthenia Gravis

Introduction/Aims Evidence linking serum mycophenolic acid (MPA) concentrations with safety outcomes in myasthenia gravis (MG) is limited. We evaluated whether single serum MPA concentrations were associated with clinically documented infection. Methods This retrospective study included acetylcholine receptor antibody‐positive MG patients treated with mycophenolate mofetil (MMF) for at least 1 year who had MPA and mycophenolic acid glucuronide (MPAG) measurement with same‐day complete blood count testing. Exact sampling time relative to MMF dosing was not uniformly documented; therefore, values were analyzed as single serum concentrations rather than confirmed trough levels. Results Among 112 MMF‐treated patients, 60 had MPA/MPAG measurement, and 10 had recent infection. Serum MPA concentration correlated strongly and positively with MPAG concentration ( r = 0.717) and moderately and inversely with lymphocyte count ( r = −0.406). Infection occurred in 0/18 low, 2/24 intermediate, and 8/18 high MPA concentration groups. Patients with infection had higher MPA concentration (median 6.15 vs. 1.80 μg/mL; Bonferroni‐adjusted p = 0.032) and higher MPA concentration per prescribed MMF dose. Discussion Higher single serum MPA concentrations were associated with recent infection. Prospective controlled studies including patients not treated with MMF are needed.