The effects of phenytoin on the penicillin-induced spike focus

A quantitative evaluation of the effects of phenytoin on penicillin-induced spike foci is reported. Phenytoin at blood levels considered within therapeutic range in humans increased spike frequency, decreased spike duration and abolished after-discharges. Spiking at weak foci was completely abolished when high concentrations of phenytoin were used. It is concluded that phenytoin affects mainly the long chain pathways whether the ultimate effects of these pathways are excitatory or inhibitory.