Which local anesthetic is the longest-acting when used without epinephrine for long-duration surgeries?

• A. Lidocaine
• B. Bupivacaine
• C. Prilocaine
• D. Mepivacaine

Answer: (B)

When a local anesthetic is used without epinephrine, the length of the nerve block is determined by how long the drug stays in the nerve tissue, which is largely a function of its lipid solubility and protein binding. The more lipid-soluble and highly protein-bound a local anesthetic is, the longer it remains in the nerve and the longer the block lasts. Bupivacaine has the greatest lipid solubility and protein binding among the common options, so it stays in the nerve tissue longest and produces the longest-duration block without epinephrine. This makes it the best choice for long-duration surgeries when vasoconstrictors are not used. Its onset tends to be slower, but the overall duration outlasts lidocaine, prilocaine, and mepivacaine in the absence of epinephrine.