Pharmacokinetics of phenytoin in routine clinic patients in Malaysia.

We estimated individual and population Michaelis-Menten pharmacokinetic parameters for phenytoin (DPH) in epileptic patients attending our neurology clinic using the computer programme. OPT. Our results agreed well with literature values but were lower than those we obtained earlier in a smaller number of patients. The Km was independent of age, weight and sex but there was a weak, correlation between Vm and body weight. We conclude that the use of population Vm and Km in normograms could lead to errors in DPH dose estimations as they correlated very poorly with patient characteristics. OPT was easy to use and sufficiently accurate for deriving dose estimates in routine patients. Its use would enable practitioners to generate their patients' own parameters for use in individual dosage adjustments. The estimates can subsequently be updated as more data become available.