What is the purpose of including a vasoconstrictor in a local anesthetic?

• A. Blocks nerve conduction
• B. Reduces blood flow to localize and slow absorption
• C. Increases diffusion of the anesthetic
• D. Neutralizes the anesthetic

Answer: (B)

In local anesthesia, a vasoconstrictor is added to narrow the blood vessels at the injection site. This reduces local blood flow, which localizes the anesthetic and slows its absorption into the bloodstream. By keeping more of the drug near the nerve fibers for a longer period, the duration of numbness is extended and the risk of systemic toxicity is lowered. The vasoconstrictor doesn’t itself block nerve conduction or neutralize the anesthetic; those roles belong to the local anesthetic agent. It also doesn’t increase diffusion—in fact, reduced blood flow helps retain the drug locally and limits rapid washout. Additionally, vasoconstriction can aid hemostasis, helping with a cleaner surgical field.