Bioavailability and clinical usefulness of low-strength tablets of phenytoin

Low-dosage (25 or 50 mg) tablets of phenytoin were developed for routine use in epilectic patients. The in vitro dissolution behavior of such tablets was similar to that of 100 mg commercial tablets. The in vivo bioavailability of the new tablets was investigated by a preliminary single-dose study in 2 patients and a steady-state study in 7 patients. The single-dose study showed that the bioavailability of the new tablets was about 80% with respect to that of the commercial product. This finding was substantially confirmed by the results of the steady-state study. Finally, the clinical usefulness of the new tablets was evaluated in 14 patients who were chronically treated with a mixed regimen of the commercial product and the 25 mg tablets. This study demonstrated the utility of the low-dosage phenytoin tablets when small dosage adjustments are needed, as it occurs frequently, due to the nonlinear pharmacokinetic of the drug.