A vasoconstrictor would decrease rate of absorption; why would we want this?

• A. Decrease rate of absorption; to slow absorption but longer duration
• B. Increase rate of absorption; to shorten duration
• C. No effect
• D. Increase rate and duration simultaneously

Answer: (A)

The main idea is that vasoconstrictors slow how quickly a drug is absorbed from the injection site. By constricting local blood vessels, they reduce blood flow, so the local anesthetic stays in the tissue longer and enters the bloodstream more slowly. This longer residence time gives a longer-lasting local effect and lowers the peak level reaching the rest of the body, reducing the risk of systemic toxicity. That’s why the best choice describes decreasing the rate of absorption to slow absorption and achieve a longer duration. If absorption were increased, the duration would be shorter and systemic exposure higher; no effect wouldn’t provide a longer-lasting local action; increasing both rate and duration isn’t the intended pharmacokinetic outcome.