Example: An epileptic patient has an average phenytoin steady state conc of 10 mg/L while taking 300 mg/day phenytoin. When the same patient was taking 400 mg/day his average s.s phenytoin conc was 20 mg/L. Calculate phenytoin Vmax and Km in this patient using a graphical method. What is the maximum phenytoin total body clearance in this patient (phenytoin bioavailability is 100%).
200
400
600
Dosing rate
mg/day
KmVmax
The highest total body clearance is observed when the plasma conc approaches zero.
