Background: Stiripentol (STP) was approved as an orphan drug in 2007 in Europe as adjunctive therapy with valproic acid (VPA) and clobazam (CLB) for Dravet syndrome. Dravet syndrome is a highly pharmacoresistant form of epilepsy, which starts in early childhood. Data about STP pharmacokinetics and interactions are still limited and in part inconsistent. The aim of our study was to analyze the effect of age, gender, daily STP dose per body weight (milligrams per kilogram), VPA, CLB, and enzyme-inducing antiepileptic drugs on STP concentration-to-dose ratio (CDR), STP clearance, and STP trough concentrations.
Methods: Retrospectively, 220 STP serum concentrations in 75 patients from 3 German Epilepsy Centers were analyzed. Analysis of variance, regression analysis, and generalized estimating equations were used for statistical analysis.
Results: Our findings confirm the nonlinear STP pharmacokinetics. At steady state, STP CDR increased with daily STP doses. Compared with patients older than 12 years, STP concentrations were decreased by 39.6% in children aged 6-12 years (P < 0.001) and by 57.5% in children younger than 6 years (P < 0.001). Phenobarbital and phenytoin decreased STP concentrations by 63.2%. This effect was highly significant (P < 0.001), despite the small number of patients (n = 7) treated with phenobarbital or phenytoin. VPA had no significant effect on STP serum concentrations, whereas STP serum concentrations were moderately but significantly increased by CLB (24.6%, P = 0.011).
Conclusions: Therapeutic drug monitoring of STP seems to be useful because of the wide variation of STP CDR, the nonlinear concentration-to-dose relationship, age-dependent pharmacokinetics, and drug-drug interactions.