[Phenytoin pharmacokinetics in young and older adults]

To study the effect of old age on phenytoin pharmacokinetics, twelve young and nine old adults aged 21.7 +/- 1.8 and 71.8 +/- 4.9 years respectively, were studied. No significant differences of phenytoin indicating the drug distribution and elimination does not change with aging. After oral administration, significant differences were observed between young and old adults for absorption, measured through oral residence half time (36.89 +/- 5.07 h in young and 29.25 +/- 8.64 h in old adults p < 0.05), absorption half time (6.91 +/- 3.6 vs 3.29 +/- 2.35 h) and maximal concentration (1.45 +/- 0.37 vs 2.0 +/- 0.79 micrograms/ml). However, absolute bioavailability of the drug was not different in both age groups (72.9 and 67.6% in young and old adults respectively). It is concluded that no modifications of phenytoin dosage are necessary in elderly people.