Inter- and intraindividual variability of riluzole serum concentrations inpatients with ALS

All patients with amyotrophic lateral sclerosis (ALS) are treated with the same dose of riluzole: 50 mg twice daily. Reasonably large interindividual differences in clearance of the drug have been reported. The relatively sma ll group of patients with high blood concentrations of riluzole has probabl y primarily influenced the efficacy and the incidence of side-effects in th e previously conducted clinical trials with riluzole. Individual dosing of the drug may, in the case of large interindividual differences in serum con centrations of the drug, be necessary in the future. Exact data concerning the plasma and serum concentrations of riluzole in patients with ALS, after standardized intake of the drug, diet and blood sampling are unknown so fa r. In this study, inter- and intraindividual. variability of serum and plas ma levels of riluzole in 21 patients with "probable" or "definite" ALS were determined. The interindividual variability of peak serum levels (coeffici ent of variation = 74%) was significantly larger than intraindividual varia bility (p < 0.001). Serum levels were not correlated with age or smoking st atus. The determination of a correlation between riluzole serum concentrati ons and survival of patients with ALS will be the aim of further studies. ( C) 2001 Elsevier Science B.V. All rights reserved.