What effect would adding a vasoconstrictor to a subcutaneous injection have on absorption?

• A. Slower absorption
• B. Faster absorption
• C. No effect
• D. Dramatic tissue damage

Answer: (A)

The rate at which a drug leaves subcutaneous tissue and enters the bloodstream mostly depends on local blood flow. A vasoconstrictor narrows small vessels, cutting down perfusion at the injection site. With less blood flow, the drug is taken up into the circulation more slowly, so absorption is slowed. This is why vasoconstrictors are used with local anesthetics—to prolong local action and reduce systemic spread. It wouldn’t speed up absorption or have no effect, and dramatic tissue damage isn’t the expected outcome when used correctly, though improper use in certain areas can cause ischemic risk.