What does pharmacokinetic variability refer to?

• A. Differing concentration at the site of action
• B. Differing response to the same concentration at the site of action
• C. Genetic differences in receptor density
• D. Variation in patient adherence

Answer: (A)

Pharmacokinetic variability is differences in the actual drug concentration reaching the site of action due to how the body handles the drug—absorption, distribution to tissues, metabolism, and elimination. These processes can vary between individuals, so the same dose can produce different exposure (drug levels) in different people, leading to different potential effects. This is about exposure, not the body’s response to that exposure. The other ideas relate to pharmacodynamics (how the body responds to a given concentration or factors like receptor density) or to adherence, which affects the amount actually taken rather than how the body processes the drug.