MACE Medication Assistant Exam Prep

Answer: B - Phenytoin is metabolized primarily by hepatic microsomal enzymes. Concomitant use of drugs that inhibit or enhance hepatic microsomal activity results in altered drug metabolism/activity level. Of the drugs choices listed above, phenytoin increases the serum levels of just amiodarone; serum levels of amiodarone are not decreased by phenytoin.

For the remaining drugs, doxycycline, cyclosporine, furosemide, and quinidine, phenytoin decreases serum levels.