If two patients achieve different blood levels after the same dose, this illustrates which type of variability?

• A. Pharmacodynamic variability
• B. Environmental variability
• C. Pharmacogenomic variability
• D. Pharmacokinetic variability

Answer: (D)

Pharmacokinetic variability is being tested. When two patients receive the same dose but reach different blood levels, it reflects differences in how the body handles the drug—absorption, distribution, metabolism, and elimination. These ADME processes can vary between individuals due to factors like organ function, age, drug interactions, and genetic differences, leading to higher or lower plasma concentrations after the same dose. This is distinct from pharmacodynamic variability, which would describe differences in the drug’s effect at a given concentration, and environmental variability, which involves external factors that affect exposure. Pharmacogenomic variability is a genetic contributor to pharmacokinetic differences, but the broad concept describing the observed difference in blood levels is pharmacokinetic variability.