抄録
Phenytoin (PHT), an anticonvulsant drug, has been reported to have different absorbing dispositions caused by differences in its preparation. With PHT there is a risk that toxic effects may appear after changing to improved absorbing preparations because of its narrow therapeutic range in the serum concentration. As a result, it is necessary to determine the appropriate prescription dose based on the serum PHT concentration and symptoms of the individual patients. In order to investigate the prescription dose of PHT during the exchange from PHT 10% powder (PHT 10) prepared in our hospital to ALEVIATIN®10% Powder (ALV 10, Dainihon Seiyaku) which is reported to have improved absorption characteristics, we investigated the serum PHT concentrations, the doses of PHT 10 and ALV 10, and the symptoms of the patients before and after the change in the PHT preparations.
The mean serum PHT concentration and the mean serum PHT concentrations to the oral doses ratio (S/D ratio) with ALV 10 in the patients prescribed the same dose (n=11) during the exchange of preparations were 7.62 (μg/mL) and 1.69 (μg/mL)/(mg/kg/day), respectively, and were larger (but not significantly so) than those of PHT 10 (4.84 and 1.06, respectively). In the 21 patients receiving the reduced doses of ALV 10, the mean serum PHT concentrations treated by ALV 10 were 7.16 and were the same as those of PHT 10, however, the mean S/D ratio of ALV 10 was 1.91 and increased (not significantly) in comparison with those of PHT 10 (1.58). In the 21 patients receiving the reduced doses of ALV 10, the oral doses and the reduction rates during the change from PHT 10 to ALV 10 were the same between the patients that kept the reduced doses (n=12) and the patients required to have additional doses of ALV 10 (n=9) after a reduction of ALV 10 treatment during the change in preparations. In the patients requiring addi tional doses of ALV 10 after using the lower doses of ALV 10, the mean serum PHT concentration and S/D ratio for PHT 10 were 4.17 and 0.87, respectively, which were significantly lower than those in the patients who could be kept on the reduced doses of ALV 10 (9.39 and 2.11, respectively). The mean serum PHT concentratios and S/D ratio in the ALV 10 were 3.97 and 1.15, respectively, which were significantly lower than those of patients who were able to stay on the reduced dose of ALV 10 (9, 56 and 2.48, respectively).
When switching to the improved absorbing PHT preparations, usually the same dose should be prescribed as the PHT 10 because of the risk that a uniform reduction in the doses according to the conversion table might cause seizures especially in the patients with low serum PHT concentrations for the lower absorbing PHT preparations.
