Serum levels of carbamazepine and cortical excitability by magnetic brain stimulation.

We investigated the correlation between serum levels of carbamazepine (CBZ) and motor excitability studied by different parameters of transcranial magnetic stimulation (TMS) in patients at the beginning of antiepileptic treatment. A total of 10 patients with complex partial seizures following stroke were treated with loading doses of CBZ. Motor evoked potential (MEP) was recorded from the thenar eminence (TE) muscles of the unaffected arm. In all patients, we studied rest and active motor threshold (rMT, aMT), MEP amplitude and cortical silent period (CSP). In three patients, intracortical inhibition (ICI) and intracortical facilitation (ICF) were measured using paired TMS at short interstimulus intervals (1-25 ms). The recording sessions were performed before treatment and after 7, 15 and 60 days (SD=16 days). Serum level of CBZ were monitored at each recording session. We observed a progressive increase in rMT and aMT until the serum levels of CBZ reached a steady state condition. No significant changes were observed in MEP amplitude, CSP, ICI and ICF. This study documents the increase of both motor threshold and drug serum levels in patients treated with loading doses of CBZ, suggesting a relationship between drug metabolism and the effect on motor cortical excitability.