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Because of its narrow therapeutic range and capacity-limited metabolism, dosage adjustment of phenytoin in epileptic patients is difficult. Currently, Bayesian method which estimates the most probable parameters of Vmax and Km for each patient based on population parameters seemed to be very useful approch for adjusting phenytoin dosage. However, published population parameters of phenytoin are variable depend on authors. Therefore, this study was performed to estimate the values of Km and Vmax in Korean. Data from 20 adult neurologic outpatients in Seoul National University Hospital whose liver ＆ renal function are normal were evaluated retrospectively. Two steady-state concentration data at two different doses were collected from each patient. In the present study, phenytoin pharmacokinetic parameters, Vmax ＆ Km, were calculated from these two dose-concentration data by using Michaelis-Mented equation. Estimated mean value of Vmax and Km were 6.72㎎/㎏/day(SD 1.34:CV 20％) and 4.77㎍/㎖(SD 2.39:CV 50％). respectively. The coefficient of variations for each parameter show significant interindividual variation which is similar to other authors´ results.
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