Which factor is a source of variation in drug responsiveness between patients?

• A. The time of day the drug is taken
• B. Rate of absorption of a drug
• C. The brand name of the drug
• D. The patient’s favorite food

Answer: (B)

Differences in how quickly a drug is absorbed into the bloodstream create variation in how patients respond. The rate of absorption determines how fast and how much of the drug reaches systemic circulation, which affects the onset, intensity, and duration of the effect. If absorption is rapid, plasma levels rise quickly, often producing a quicker and stronger response; if it’s slower, the onset is delayed and peak effect may be reduced. Many patient-specific factors influence absorption rate, including gastric emptying time, intestinal motility and surface area, pH, and interactions with food or other substances. This makes absorption rate a key driver of interpatient differences in drug response. Other options, like the time of day, brand name, or a person’s favorite food, don’t consistently account for why responses vary between individuals.