Example: The steady state phenytoin plasma conc in an epileptic patient was 10 mg/L when the dose was 300 mg/day and was 20 mg/L when the dose was 400 mg/day. Using the direct linear plot calculate the dose required to achieve a steady state plasma conc of 15 mg/L. What will be the steady state if a dose of 700 mg/day is administered to the same patient. (phenytoin bioavailability is 100%).
200
400
600
Dosing rate
mg/day
Dose
15 mg/L
KmVmax
When the dose is larger than Vmax the drug will keep accumulating in the body and steady state will never be achieved.
