Effects of phenytoin administration on vestibular function in the rat

Acute or chronic treatment of epileptic patients with phenytoin is often associated with the appearance of disturbances such as postural impairment and ocular nystagmus, probably due to high toxic plasma levels of the drug. We describe the changes in spontaneous electrical activity of vestibular units in cerebellectomized rats following an acute nontoxic dose of phenytoin, in static conditions and after macular stimulation. Administration of phenytoin induced an inhibition of Deiters cells and a drug level-dependent biphasic effect (excitation followed by inhibition) on medial and superior vestibular cells. The experiments pointed to a direct action of phenytoin on the vestibular nuclear complex, indicating that postural and motor disturbances are not only cerebellar but also vestibular in origin.