Which statement best defines a drug's therapeutic range?

• A. The time to reach peak concentration after dosing
• B. The maximum tolerated dose
• C. The plasma concentration range where a drug is effective without being toxic
• D. The concentration at which a drug is excreted

Answer: (C)

The therapeutic range describes the range of plasma drug concentrations that provide the desired therapeutic effect without causing unacceptable toxicity. If levels are below this window, the drug may be ineffective; if levels exceed it, toxicity becomes more likely. This concept centers on blood concentration, not how long it takes to reach peak, not the maximum tolerated dose, and not a specific excretion level. For drugs with a narrow therapeutic window, clinicians actively monitor blood levels and adjust dosing to stay within this safe, effective range.