Population pharmacokinetics of riluzole in patients with amyotrophic lateral sclerosis.

OBJECTIVES: To characterize the population pharmacokinetic of riluzole in patients with amyotrophic lateral sclerosis (ALS). METHODS: One hundred patients with ALS who were participating in a multicenter phase III dose-ranging trial of riluzole were sampled on 179 visits. The sampling strategy (two samples per visit) was varied across patients to define the population kinetic profile (full screen). Riluzole plasma levels were determined by HPLC, and the data were analyzed by nonlinear mixed-effect modeling (NONMEM program) with use of a one-compartment structural model. The model incorporated interoccasion (visit-to visit) variability. RESULTS: In the basic one-compartment pharmacokinetic model, interindividual variability in plasma clearance (51.4%) was higher than intraindividual (visit-to-visit) variability (28.0%), indicating uniform pharmacokinetic behavior during long-term therapy. Riluzole clearance was independent of dosage (25 to 100 mg twice daily), treatment duration (up to 10 months), age, and renal function; gender and smoking were the most important patient covariates, with hepatic function having lesser influence. Typical value of clearance was 51.4 L/hr for a nonsmoking male patient. It was 32% lower in women than in men and 36% lower in nonsmokers than in smokers. Gender- and smoking-related variations in riluzole exposure at the recommended dosage (50 mg twice daily) were within the range of exposures achieved (with no untoward effect) in this dose-ranging study. CONCLUSION: The pharmacokinetics of riluzole has been characterized in patients during long-term therapy. Riluzole clearance is independent of dose and treatment duration. Within-patient variability is low. Gender and smoking status are the main covariates to explain interpatient variability.

The Rilutek (riluzole) Global Early Access Programme: an open-label safety evaluation in the treatment of amyotrophic lateral sclerosis.

OBJECTIVES: This study had two main objectives: 1. To enable patients with amyotrophic lateral sclerosis (ALS) who had not participated in previous riluzole trials to receive riluzole therapy, and 2. To expand safety experience with the drug in a broad patient population. METHODS: This was a Phase IIIb multicentre, multinational, open-label, uncontrolled single treatment study of riluzole. Patients with diagnosed possible or probable ALS were administered 100 mg of riluzole/day (50 mg b.i.d.). Clinical and laboratory adverse events were recorded every month for the first 3 months and thereafter at 3-monthly intervals. RESULTS: 8383 patients from 44 countries were entered into the study; 7916 of these patients with recorded data were administered the study drug. The mean duration of riluzole treatment was 202.1 days, with a range of 1-630 days. The most frequently reported serious and non-serious adverse events were common symptoms of ALS (respiratory symptoms and dysphagia), and only 1.9% of serious adverse events were considered to be related to the study drug. CONCLUSIONS: The safety results with this broad population (over 10% of the estimated ALS population worldwide) were consistent with those previously reported from placebo-controlled trials. No increase in adverse events and no unexpected adverse events were observed.