Pharmacokinetics: why do certain drugs follow zero-order kinetics?

Question

I understand that alcohol and phenytoin are two examples of drugs that follow zero-order kinetics. Why do these two particular drugs follow zero-order kinetics as opposed to first-order kinetics?

Answer 1

A drug will have zero order kinetics of when it’s metabolic route of elimination is saturated. For alcohol, the amount of alcohol dehydrogenase (metabolic clearance route) is low relative to the amount of alcohol present following ingestion. For phenytoin, the key CYP450 enzymes are saturated at therapeutic doses.

Does this make sense?