This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
Regarding phenytoin all are true except ? 
Select and explain. 
A. Potent microsomal enzyme inducer, B. Highly protein bound, C. At lower concentration it follows zero order kinetics, D. With increasing dose, the VA increases.
C: At lower concentration it follows zero order kinetics
Answer: C: At lower concentration it follows zero order kinetics 
Explanation: Ans. is 'c' i.e., At lower concentration it follows zero order kinetics o The kinetics of metabolism of phenytoin is capacity limited; changes from first order to zero order over the therapeutic range, i.e., at lower concentration it follows first order kinetics and changes to zero order at higher doses. About other options o Phenytoin is a potent enzyme inducer. o It is 80-90% bound to plasma protein. o T1/2 increases with dose because clearance progressively decreases as dose is increased.