In pharmacodynamics, what is meant by binding affinity versus efficacy?

• A. Affinity is binding strength; efficacy is the ability to produce a maximal biological response after binding.
• B. Affinity is how quickly a drug is eliminated; efficacy is how it's metabolized.
• C. Affinity measures toxicity; efficacy measures absorption.
• D. Affinity and efficacy are the same concept.

Answer: (A)