What does a narrow therapeutic index indicate about a drug?

• A. It has a wide margin of safety
• B. Small changes in dose can lead to severe effects
• C. It is ineffective at lower doses
• D. It is suitable for over-the-counter use

Answer: (B)

A narrow therapeutic index indicates that small changes in the dosage of a drug can lead to significant and potentially severe effects. This means that the range between the minimum effective dose and the minimum toxic dose is quite small. As a result, careful monitoring of drug levels and patient response is essential when a medication with a narrow therapeutic index is used. It emphasizes the importance of adhering to prescribed dosages and monitoring for side effects, as even a slight increase in dosage could result in toxicity, while a slight decrease might result in treatment failure. Understanding this concept is crucial for safe medication management, particularly in patient populations that may be more sensitive to changes in drug levels, such as those with existing health conditions.