Valproic acid has a __________ affinity for blood plasma protein.

• A. Low
• B. Moderate
• C. No affinity
• D. High

Answer: (D)

High affinity for plasma proteins is shown by valproic acid, which binds extensively to albumin in the blood. About 90% or more of the drug in circulation is bound, leaving only a small free fraction to exert effects, be distributed, or be cleared. This strong binding means most of the drug isn’t freely active at any moment, and it also sets the stage for possible interactions with other highly bound drugs, where displacement can raise the free drug level and toxicity risk. If the affinity were low or nonexistent, a larger portion would be unbound and active, changing both effects and clearance; a moderate binding level wouldn’t align with the well-established high binding of valproate.