Chronic treatment with phenytoin in rats: effects of peripheral nervous system.

60 albino Sprague-Dawley female rats, 250 g of body weight, were treated for 6 months with phenytoin 30 mg/100 g/die per os (mean plasma levels: 10-20 gamma/ml). Between 75 and 90 days of treatment motor and sensory nerve conduction velocities were examined along the tail (Miyoshi and Goto, 1973; Fiaschi et al., 1977) in 15 treated animals and in 10 untreated control animals. A slowing of sensory conduction velocity was shown in 6 treated animals (40%); in 2 of them (13%) the motor conduction velocity was also showed. 25 treated rats were controlled with the same neurophysiologic methods after 165-180 days of PHT treatment in comparison with 10 controls; a slowing of sensory conduction velocity was observed in 14 treated rats (56%) and a slowing of motor conduction in 5 of them (20%). The hystological and ultrastructural study carried out on the sciatic nerves of all animals revealed changes of myelinated fibres only in the animals with slowed motor conduction velocity. The non-myelinated fibres were apparently normal.