A phase I clinical trial of dextromethorphan in intractable partial epilepsy

We conducted an open-label pilot study of dextromethorphan (DM) in intractable partial epilepsy with the following objectives: a preliminary evaluation of the drug's safety and efficacy in the epileptic patient and a definition of a concentration range which can be safely achieved in future studies. Sixteen patients with drug-resistant, localization-related epilepsies entered the trial. After an 8-week baseline period, DM was added to the existing antiepileptic drugs at a dose of 40 and 50 mg every 6 h (160 and 200 mg/day). Each treatment period lasted 8 weeks. Seizure control improved after administration of DM, especially in the group of intermediate and slow metabolizers. Two patients, however, experienced increased seizure frequency and withdrew from the study. Adverse effects during DM administration were mild and transient. DM was well tolerated even in patients with high plasma levels of the drug (up to 15020 ng/dl). Our results indicate that DM is safe and effective in the treatment of comedicated patients with intractable partial epilepsies.