Increased depressant effect of phenytoin sodium as compared to carbamazepine on cortical excitability: A transcranial magnetic evaluation

To evaluate the effect of monotherapy (phenytoin sodium (DPH) and carbamazepine (CBZ) on the threshold intensity (TI), cortical latency (CL), central conduction time (CCT), using transcranial magnetic stimulation (TMS). A single pulse transcranial magnetic stimulation was used for recording the motor-evoked potentials (MEP) from the thenar muscles of both hands, in 36 patients with well-controlled epilepsy on monotherapy, with normal EEG and imaging studies. The TI, CL, CCT and the MEP amplitude were recorded and compared with 20 healthy controls. The threshold intensity was significantly higher in patients on DPH, (P<0.05) with a significant decrease in the MEP amplitude when compared with controls (P<0.05). Anticonvulsants alter the excitability of human motor pathways in epileptic subjects. This effect differs among the drugs used; DPH had a greater depressant effect on the excitability than CBZ in the present study.