Drugs bound to plasma proteins mainly affect which pharmacokinetic parameter?

Drugs bound to plasma proteins mainly affect which pharmacokinetic parameter?

• A. Onset
• B. Duration
• C. Intensity
• D. Rate of Absorption

Answer: (B)

Protein binding creates a reservoir in the bloodstream: only the unbound drug can reach the site of action and be cleared. As free drug is eliminated, bound drug dissociates to replace it, slowing overall clearance and prolonging the effect. So, binding to plasma proteins mainly extends the duration of action. Onset depends on how quickly the free drug appears at the target, rate of absorption is about how the drug enters the system, and intensity relates to the actual free concentration at the site—both are influenced by binding, but the lasting effect is governed most by the reservoir effect and slower clearance, i.e., duration.

Protein binding creates a reservoir in the bloodstream: only the unbound drug can reach the site of action and be cleared. As free drug is eliminated, bound drug dissociates to replace it, slowing overall clearance and prolonging the effect. So, binding to plasma proteins mainly extends the duration of action. Onset depends on how quickly the free drug appears at the target, rate of absorption is about how the drug enters the system, and intensity relates to the actual free concentration at the site—both are influenced by binding, but the lasting effect is governed most by the reservoir effect and slower clearance, i.e., duration.