Answer
Adrenaline narrows local blood vessels, helping bupivacaine remain near the injection site for longer and reducing its rate of systemic absorption.
Sources for this answer
- Bupivacaine & Adrenaline (Epinephrine) Injection B.P. 0.25% w/v 1 in 200,000 — Current selected SmPCemc · Summary of Product Characteristics
- NHS Specialist Pharmacy Service