Which two pharmacological properties depend on a drug's chemical structure?

• A. Potency and efficacy
• B. Affinity and intrinsic activity
• C. Bioavailability and half-life
• D. Selectivity and safety

Answer: (B)

The key idea is how a drug’s chemical features govern its interaction with a target receptor—the structure-activity relationship. Affinity, or how tightly a drug binds to its receptor, comes from how well the molecule fits the binding pocket—shape, charge, hydrogen-bond donors/acceptors, and hydrophobic contacts shaped by its structure. Intrinsic activity, the ability of the bound drug to activate the receptor and produce a response, also hinges on structure because certain functional groups and conformations stabilize the receptor in its active form. Together, these two properties are direct reflections of the drug’s chemical structure.

Other options mix in pharmacokinetic factors or broader effects. Potency is influenced by both binding strength and how the body handles the drug, so it’s not as direct a readout of just structure. Bioavailability and half-life depend heavily on absorption, distribution, metabolism, and excretion, which involve many properties beyond receptor binding. Selectivity and safety are important but encompass broader off-target interactions and toxicology, not only the primary receptor binding and activation.