Question

Why dose dependent kinetics known as non linear kinetics?

Answer 1

A second consequence is that, because clearance decreases, apparent half-life increases from about 12 hours at low phenytoin concentrations to as long as a week or more at high concentrations. This means that

i. the time to reach steady state can be as long as 1-3 weeks at phenytoin concentrations near the top of the therapeutic range

ii. in the therapeutic range, the phenytoin concentration fluctuates little over a 24 hour period allowing once daily dosing and sampling for drug concentration monitoring at any time between doses

iii. if dosing is stopped with concentrations in the toxic range, phenytoin concentration initially falls very slowly and there may be little change over a number of days.