Which drug pair is associated with a clinically significant interaction when the second drug is added to the first?

Which drug pair is associated with a clinically significant interaction when the second drug is added to the first?

• A. Verapamil and Amlodipine
• B. Verapamil, Metoprolol
• C. Metoprolol and Diltiazem
• D. Verapamil and Furosemide

Answer: (B)

When two drugs both slow the heart’s electrical activity, adding the second to the first can produce a dangerous drop in heart rate and impaired conduction. Verapamil slows AV nodal conduction and lowers heart rate; metoprolol does the same by blocking beta-1 receptors. Together, their effects sum, increasing the risk of symptomatic bradycardia, high-grade AV block, hypotension, or worsening heart failure. This makes their combination a well-known clinically significant interaction, especially in patients with preexisting conduction issues. Other pairs can carry risks too, but the verapamil–metoprolol combination is the classic example of a strong pharmacodynamic interaction due to dual suppression of cardiac conduction and rate. If such a combination is used, careful monitoring and dose adjustments are essential, and it’s often avoided in those with conduction abnormalities.

When two drugs both slow the heart’s electrical activity, adding the second to the first can produce a dangerous drop in heart rate and impaired conduction. Verapamil slows AV nodal conduction and lowers heart rate; metoprolol does the same by blocking beta-1 receptors. Together, their effects sum, increasing the risk of symptomatic bradycardia, high-grade AV block, hypotension, or worsening heart failure. This makes their combination a well-known clinically significant interaction, especially in patients with preexisting conduction issues. Other pairs can carry risks too, but the verapamil–metoprolol combination is the classic example of a strong pharmacodynamic interaction due to dual suppression of cardiac conduction and rate. If such a combination is used, careful monitoring and dose adjustments are essential, and it’s often avoided in those with conduction abnormalities.