A client receiving metoprolol (Lopressor), a substrate of the CYP2D6 system, is started on ...

Correct Answer: 3
Rationale 1: Lopressor, not amiodarone, is more likely to be toxic, as it will take longer to be inactivated.
Rationale 2: It is not necessary to administer the drugs on an empty stomach; this will not alter the metabolism by the CYP enzyme system.
Rationale 3: The CYP enzyme system determines the speed at which most drugs are metabolized in the liver. When one drug inhibits the action of the same isoenzyme system, other drugs being metabolized by this same system might not be inactivated as quickly, leading to prolonged effects of the drug.
Rationale 4: It would not be necessary to administer the drugs two hours apart; this would not alter their metabolism by the CYP enzyme system.
Global Rationale: The CYP enzyme system determines the speed at which most drugs are metabolized in the liver. When one drug inhibits the action of the same isoenzyme system, other drugs being metabolized by this same system might not be inactivated as quickly, leading to prolonged effects of the drug. Lopressor, not amiodarone, is more likely to be toxic, as it will take longer to be inactivated. It is not necessary to administer the drugs on an empty stomach; this will not alter the metabolism by the CYP enzyme system. It would not be necessary to administer the drugs two hours apart; this would not alter their metabolism by the CYP enzyme system.