Population pharmacokinetics of phenytoin in South African black patients

In the routine care of 37 patients at the epilepsy outpatient clinic of Baragwanath Hospital, Johannesburg, 100 steady-state serum phenytoin concentrations were measured. Total and free phenytoin as well as albumin serum concentrations were determined. Computer analysed data were fitted to the Michaelis-Menten model for steady-state serum concentrations. As a function of the Michaelis-Menten constant (P less than 0.1) total serum phenytoin concentration provided a significantly better fit than free phenytoin combined with albumin serum concentrations. The Vm and Km of 6.5 mg/kg/d and 13.6 mumol/l respectively, determined by using total serum concentration, could be to estimate phenytoin dosage requirements in a hospital population.