Given constant arterial concentration, what happens to tissue concentration and rate of uptake over time?

Given constant arterial concentration, what happens to tissue concentration and rate of uptake over time?

• A. Tissue concentration would decrease; uptake rate would increase
• B. Tissue concentration would remain constant; uptake rate would remain constant
• C. Tissue concentration would increase; uptake rate would increase
• D. Tissue concentration would increase; uptake rate would decrease

Answer: (D)

With constant arterial concentration, drug transfer into tissue is driven by the concentration gradient between blood and tissue. As the drug moves into the tissue, tissue concentration rises. Since the arterial level is fixed, the gradient diminishes over time, decreasing the driving force for further uptake. Consequently, tissue concentration increases over time, but the rate of uptake decreases as equilibrium is approached. This matches the idea that early on uptake is fast and slows down later as the gradient shrinks.

With constant arterial concentration, drug transfer into tissue is driven by the concentration gradient between blood and tissue. As the drug moves into the tissue, tissue concentration rises. Since the arterial level is fixed, the gradient diminishes over time, decreasing the driving force for further uptake. Consequently, tissue concentration increases over time, but the rate of uptake decreases as equilibrium is approached. This matches the idea that early on uptake is fast and slows down later as the gradient shrinks.