Which concept refers to a drug being both effective and requiring monitoring?

The concept that refers to a drug being both effective and requiring monitoring is the therapeutic index. This measure indicates the range of doses that produces the desired effect without causing significant adverse effects. A drug with a narrow therapeutic index means there is a small margin between effective doses and toxic doses, necessitating careful monitoring of drug levels and patient responses to ensure safety and efficacy.

In contrast, bioequivalence refers to the comparison of two drug formulations to determine if they have similar bioavailability and effects in the body. An exceptional drug might refer to a drug with unique or uncommon properties, but it does not inherently relate to effectiveness and monitoring. The mechanism of action describes how a drug exerts its effects at a molecular level and does not imply anything about the need for monitoring or its overall effectiveness in practice.