Which statement about vasoconstrictors with local anesthetics is true?

• A. They shorten duration
• B. They increase peak blood levels
• C. They decrease systemic absorption and prolong duration
• D. They have no effect on bleeding

Answer: (C)

Vasoconstrictors added to local anesthetics work by constricting blood vessels in the area, which slows the absorption of the anesthetic into the bloodstream. This keeps more of the drug localized in the tissue, lowers the peak plasma concentration, and extends the duration of anesthesia because the drug is cleared more slowly from the local site. It also helps reduce bleeding by decreasing local blood flow. Therefore, the statement that is true is that they decrease systemic absorption and prolong duration. They do not shorten duration, they do not increase peak blood levels, and they do have an effect on bleeding (reducing it).