Lymphocyte counts and infection rates: Long-term fingolimod treatment in primary progressive MS

OBJECTIVE: To evaluate lymphocyte counts and incidences of infections in patients with primary progressive MS (PPMS) receiving fingolimod 0.5 mg/d or placebo over 5 years during the INFORMS study, to assess infection rates with longer-term treatment. METHODS: INFORMS was a randomized, multicenter, double-blind, placebo-controlled, parallel-group, phase 3 study of the sphingosine 1-phosphate receptor modulator fingolimod in patients with PPMS. Lymphocyte counts and incidences of infections were compared in patients receiving fingolimod or placebo. Infection rates were assessed in patients receiving fingolimod according to nadir and mean absolute lymphocyte count (ALC). RESULTS: Overall, 336 patients received fingolimod 0.5 mg/d (total exposure: 908.1 patient-years), and 487 received placebo (1,423.5 patient-years). In patients receiving fingolimod, mean ALC decreased by approximately 70% in the 2 weeks following treatment initiation and remained stable throughout the study. The incidences of all infections in the fingolimod and placebo groups were similar (53.6 vs 51.9 per 100 patient-years). The most common infections in patients receiving fingolimod were urinary tract infections (5.7 per 100 patient-years), upper respiratory tract infections (4.2 per 100 patient-years), and influenza (3.2 per 100 patient-years); incidences were similar in the placebo group (5.9, 4.2, and 3.1 per 100 patient-years, respectively). There was no apparent association between nadir or mean ALC and incidence of infection-related adverse events. CONCLUSIONS: In patients with PPMS, long-term treatment with fingolimod 0.5 mg/d for up to 5 years led to an expected decrease of approximately 70% in mean ALC and did not appear to correlate with increased risk of infection. CLASSIFICATION OF EVIDENCE: Because this is a secondary analysis, this study provides Class II evidence that long-term PPMS treatment with fingolimod decreased mean ALC by approximately 70%, but did not significantly increase infection risk.