Pharmaceutics Distribution Of Drugs Practice Exam

How does a more rapid perfusion rate affect the rate at which drug distribution approaches equilibrium?

It increases the rate toward equilibrium. It decreases the rate toward equilibrium. It has no effect on the rate toward equilibrium. It delays distribution only in lipophilic drugs.

Correct Answer:

It increases the rate toward equilibrium.

Explanation:

When distribution is perfusion-limited, the speed at which drug concentrations in tissue reach equilibrium with plasma is governed by how much blood flow delivers the drug to the tissue. Increasing perfusion means more drug is delivered to tissues per unit time, so tissue concentrations rise faster and reach the equilibrium point with plasma more quickly. In other words, a higher perfusion rate speeds up the approach to distribution equilibrium. If distribution were limited by tissue permeability rather than blood flow, changing perfusion would have less effect, but under perfusion-limited conditions the rate toward equilibrium increases with perfusion.

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