Which local anesthetic typically has the longest duration of action among common agents?

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

Answer: (C)

The main concept here is how the duration of a local anesthetic is determined. Drugs that are more lipid-soluble and more tightly bound to proteins tend to stay near the nerve longer and are cleared more slowly, giving a longer blockade. Bupivacaine fits that pattern best among common agents: it’s highly lipid-soluble and highly protein-bound, so once it penetrates the nerve membrane, it lingers and produces a longer-lasting effect. Its onset can be slower than some others, but the duration is markedly extended, especially when used with a vasoconstrictor like epinephrine to reduce uptake into the bloodstream.

In contrast, procaine, lidocaine, and prilocaine are less lipid-soluble and have lower protein binding, so their blocks wear off more quickly as the drug diffuses away and is absorbed systemically. Lidocaine and prilocaine provide intermediate duration, with procaine typically shorter.

So, the local anesthetic that typically lasts the longest is bupivacaine.