Analysis of Concentrations of Monomethyl Fumarate in Patients with Multiple Sclerosis: Result from Routine Health Care

Abstract

Dimethyl fumarate is used to treat patients with relapsing-remitting multiple sclerosis. After ingestion, it is rapidly hydrolyzed to the active primary metabolite monomethyl fumarate. The main objective of our study was to analyze serum concentrations of monomethyl fumarate during routine health care in patients with multiple sclerosis treated with a fixed dose of dimethyl fumarate. In the pilot cross-sectional study, data from 42 patients treated with dimethyl fumarate at a dose of 240 mg twice daily were collected. Concentrations of the active metabolite monomethyl fumarate were determined at 1-8 h (median, 3 h) or 10-14 h (median, 13 h) after taking the dose. The relationship between monomethyl fumarate concentrations and absolute lymphocyte count was evaluated. Concentrations of monomethyl fumarate ranged from 2.5-3177.9 μg/L, with most concentrations being undetectable approximately 10 hours after administration. In the 1-8 h (median, 3 h) post-dose subgroup, the concentration/dose ratio ranged widely from 0.04-6.62. The median concentration of monomethyl fumarate in the group with the absolute lymphocyte count <0.8 x 10^9/l was more than four times higher than in the group with the absolute lymphocyte count ≥0.8 x 10^9/l (median 440.1 μg/L versus 98.4 μg/L). The wide interindividual variability in monomethyl fumarate pharmacokinetics could contribute to the differential response to dimethyl fumarate in multiple sclerosis patients. A nonsignificant but noticeable trend was observed in the relationship of higher serum monomethyl fumarate concentrations to absolute lymphocyte counts.