FPGEE for National Association of Boards of Pharmacy (NABP) Practice Exam

What is the active metabolite of primidone?

1. Phenytoin

2. Phenobarbital

3. Carbamazepine

4. Valproate

The correct answer is: Phenobarbital

Primidone is an anticonvulsant medication primarily used to control seizures. When it is administered, the body metabolizes it into two principal metabolites, one of which is phenobarbital. Phenobarbital itself possesses anticonvulsant properties and contributes to the overall therapeutic effects of primidone. This connection is significant for understanding how primidone operates within the context of epilepsy treatment. Primidone’s conversion to phenobarbital provides an extended mechanism of action that facilitates the management of seizure disorders, particularly for patients who may benefit from the more sedative effects and extended duration of anticonvulsant activity that phenobarbital offers. The other options, while they are anticonvulsants, do not serve as metabolites of primidone. Phenytoin, carbamazepine, and valproate are distinct drugs with different action mechanisms and metabolic pathways, which distinguishes them from phenobarbital in this context. Therefore, phenobarbital is recognized as the active metabolite of primidone.