Comparison of the effectiveness of two oral phenytoin products and chronopharmacokinetics of phenytoin.

A cross-over study was carried out in 14 epileptic patients to compare the steady-state serum phenytoin concentrations produced by two phenytoin formulations (Phenytoin Sodium and Epanutin). Differences in steady-state phenytoin concentrations following a change from one product to the other were not significant, indicating that the two brands manifest equivalent therapeutic efficacy. The results suggest that no overall dosage adjustments are required when switching from one brand to the other. Chronopharmacokinetic parameters of a single 300-mg dose of phenytoin, given at 08.00 and 20.00 hours, were studied in 10 healthy, male volunteers under controlled conditions. No evidence was found that circadian rhythms influenced absorption and disposition.