Which term describes the interaction where two or more drugs are used at the same time and the combined effect is less than the sum?

Which term describes the interaction where two or more drugs are used at the same time and the combined effect is less than the sum?

• A. Drug interaction classifications
• B. Additive effects
• C. Synergistic interactions
• D. Antagonistic interactions

Answer: (D)

Antagonistic interactions occur when two drugs are given together and one diminishes the effect of the other, so the overall effect is smaller than the sum of their individual effects. This happens when one drug blocks the receptor or interferes with the other's signaling, or when pharmacokinetic factors reduce the concentration of the other drug at the site of action. For example, an opioid antagonist like naloxone can blunt the effect of morphine. This differs from additive effects, where the total is exactly the sum of each drug’s effect, and from synergistic effects, where the total is greater than the sum.

Antagonistic interactions occur when two drugs are given together and one diminishes the effect of the other, so the overall effect is smaller than the sum of their individual effects. This happens when one drug blocks the receptor or interferes with the other's signaling, or when pharmacokinetic factors reduce the concentration of the other drug at the site of action. For example, an opioid antagonist like naloxone can blunt the effect of morphine. This differs from additive effects, where the total is exactly the sum of each drug’s effect, and from synergistic effects, where the total is greater than the sum.