A vasodilator would ______ rate of absorption.

• A. Decrease rate of absorption
• B. Irregular rate of absorption
• C. No change in rate of absorption
• D. Increase rate of absorption

Answer: (D)

Absorption rate depends on how much blood is flowing to the site where the drug is entering the body. A vasodilator widens the blood vessels, increasing local blood flow. With more blood moving away from the administration site, the drug can leave the site and enter the bloodstream faster, so the rate of absorption increases. This effect is especially evident for topical, subcutaneous, or intramuscular administration, and can also influence oral absorption to some extent when gut blood flow is enhanced. Decreased rate would come from vasoconstriction, irregular rate from inconsistent perfusion, and no change would occur if blood flow weren’t a limiting factor; but with vasodilation, the rate generally goes up.