Rapid and slow release phenytoin in epileptic patients at steady state: comparative plasma levels and toxicity

Phenytoin plasma level and toxicity data were compared in a three-way crossover study performed in 18 patients at steady state. Formulations compared were a rapid and a slow release capsule and an oral solution. Plasma concentration-time integrals and maximum plasma phenytoin levels were significantly greater for the rapid release capsule and solution than for the slow release capsule. The incidence of nystagmus and toxicity did not differ for the three treatments, but the occurrence of mental symptoms was more frequent for the oral solution, possibly because of the solvent used in this formulation.