Saturable Drug Metabolism
When metabolism becomes saturated, drug elimination changes from "first-order" (exponential decline in Cp) to "zero-order" (linear decline in Cp).
Most drugs have first-order elimination at therapeutic Cp. Drugs that have enzyme saturation at or near the therapeutic Cp include phenytoin, aspirin, alcohol, fluoxetine and verapamil.
Adjust dose and observe the effect on the Cp-time curve.