Which term describes the degree to which a drug binds to a receptor compared with other receptors?

• A. Efficacy
• B. Potency
• C. Affinity
• D. Safety

Answer: (C)

Affinity is the degree to which a drug binds to a receptor, reflecting how tightly it fits and how readily it stays bound. When a drug has high affinity for a receptor, it tends to bind that receptor preferentially over others, giving selective effects even at lower concentrations. Potency describes how much drug is needed to produce a given effect and is influenced by affinity but also by how the body processes the drug and the receptor's signaling. Efficacy refers to the maximal effect a drug can produce, not its binding strength. Safety concerns relate to adverse effects and are not about binding affinity. So, the term that best fits describes binding strength and selectivity across receptors: affinity. Lower dissociation constants (Kd) indicate higher affinity, meaning tighter binding to the target receptor.