Population pharmacokinetics of phenytoin in Singapore Chinese

Summary The pharmacokinetics of phenytoin was studied in 66 epileptic Chinese children and adults. The data were analysed by the population approach, using the non-linear mixed effect model, in the MULTI (ELS) program. There was no age or gender-related effect on either the apparent maximum elimination rate (k_max) or Michaelis-Menten constant (K_M). K_max was related to body weight 0.656. The population pharmacokinetics was similar in children and adults. K_max and K_M were estimated to be 30.72 mg·kg^–0.656 day^–1 and 2.307 mg·l^–1, respectively. K_max was higher than reported values, and K_M was comparable to that reported in a study in Japanese, but was much lower than that reported in studies of European patients. The inter-individual variability of K_M (CV 65.58%) was substantially higher than that of k_max (CV 28.49%), and the residual (intra-individual) variability was found 21.33% (CV).