Which statement best defines a drug's therapeutic range?

• A. The time to peak concentration
• B. The minimum effective dose
• C. The concentration where toxicity begins
• D. The plasma concentration range where a drug is effective without being toxic

Answer: (D)

The therapeutic range is the plasma concentration window in which a drug provides clinical benefit without causing unacceptable toxicity. This range sits between the level needed to achieve a therapeutic effect (the minimum effective concentration) and the level at which toxic effects begin (the upper bound). Staying within this window helps ensure the drug is both effective and safe.

Other concepts described by the distractors don’t capture this window: one refers to how quickly the drug reaches its peak in the blood, another is about the amount needed to produce an effect (a dose, not a concentration), and the other points to where toxicity starts, which defines only the upper limit, not the full safe range.