Bimodal evoked potentials during long-term therapy with conventional or slow release preparations of carbamazepine and valproic acid in children and adolescents with epilepsy

The measurement of evoked potentials (EPs) may be particularly useful in clinical neuropharmacology for investigation of drug effects of afferent nerve conduction within CNS. The study aims at estimating the long term effects of conventional or slow release formulation (CR) of carbamazepine (CBZ) and valproid acid (VPA) on visual (VPA) and brainstem auditory (BAEP) evoked potentials. Investigation covered 125 patients 8 to 18 years old to whom both formulations of CBZ or VPA were administered in monotherapy. Everyone received a drug dosage which gave an adequate therapeutic plasma concentration and satisfactory seizure control. Antiepileptic drugs (AEDs) plasma levels were measured by means of fluorescence polarization immunoassay method aided of TDx Analyzer (Abbott, Diagnostic). EPs were registered by means of Multiliner (Toennies, Germany). A pattern of reversal stimulation for VEP was used. The latencies of N75, P100, N145 as well as interpeak amplitudes of N75/P100, P100/N145 were evaluated. The following BAEP parameters were considered: morphology of the potential, absolute latencies of waves I, III, V and I-III, III-V, I-V. EP were always performed in the same conditions and with the same equipment for the epileptic and control groups. The obtained values were compared with age-matched control group. The following BAEP abnormalities were observed: prolonged absolute latencies of waves I, III, V as well as prolonged IPLs I-III. The BAEP V/I amplitude ratio and morphology of the waves were normal in all patients. The VEPs abnormalities manifested as prolongation of P100 or N145 latencies and reduction of amplitudes N75/P100, P100/N145. Results of these electrophysiological studies with CBZ and VPA demonstrate that EP are sensitive, noninvasive reflectors of AEDs effects within the CNS.