True or False: The plasma concentration is typically lower than the concentration at the site of absorption.

• A. False
• B. True
• C. Sometimes
• D. Not determinable

Answer: (B)

When a drug is given, it first sits at the site of absorption in a relatively small, local space (for an oral drug, the intestinal lumen) with a fairly high concentration from the dosage form. To get into the bloodstream, it must cross the gut wall, which takes time. As the drug leaves the lumen and enters the blood, the lumen’s drug concentration falls while the plasma concentration rises. But plasma is a large, well-mixed compartment and the drug is also being distributed to tissues and cleared, which keeps its concentration in plasma typically lower than the local concentration at the absorption site during the absorption phase. So, in general, the site of absorption has a higher concentration than plasma, making the statement true.