Usefulness of monitoring mycophenolic acid exposure in systemic sclerosis-related interstitial lung disease: a retrospective cohort study.

Background: Systemic sclerosis-related interstitial lung disease (SSc-ILD) represents a significant cause of morbidity and mortality in Systemic Sclerosis (SSc). Mycophenolate mofetil (MMF) is currently the first line treatment for SSc-ILD. There is no recommendation on the dosage of mycophenolic acid (MPA) blood concentrations, so we aimed to study the correlation between MPA exposure and respiratory outcomes in this population.

Methods: We conducted a retrospective cohort study of SSc-ILD patients treated with MMF in our center. According to our policy, a complete patient evaluation was performed approximately one year after MMF initiation, during which the mycophenolic acid (MPA) residual rate (RR) was measured. We analyzed the association between RR and changes in forced vital capacity (FVC) and diffusion capacity for carbon monoxide (DLCO) over time.

Results: Forty-three SSc-ILD patients were included. Patients with higher RR levels (≥ 1.5 mg/L) had a significantly better FVC evolution with a higher proportion of stabilization and lower proportion of FVC decrease (p = 0.024). RR above 1.5 mg/L was a predictive factor of reduced FVC decline compared with lower RR levels adjusting for MMF dose and duration of MMF exposure (p = 0.008). There was no difference regarding DLCO outcome.

Conclusion: Our study suggests that optimal MPA exposure, as indicated by RR levels, may better protect against FVC decline in SSc-ILD patients treated with MMF. Routine monitoring of MPA exposure could be beneficial in optimizing treatment outcomes. Prospective, multicenter studies are needed to further explore the relationship between MPA exposure and clinical outcomes in SSc-ILD.