Which local anesthetic is least likely to cause an allergic reaction?

Lidocaine is considered the local anesthetic least likely to cause an allergic reaction due to its chemical structure and the fact that it is an amide-type anesthetic. Amide local anesthetics, including lidocaine, are less commonly associated with allergic reactions compared to ester-type anesthetics. This is primarily because allergic reactions to local anesthetics are often related to the metabolites or preservatives present in the formulation, especially in esters.

In contrast, other local anesthetics like procaine (an ester) have a higher potential to induce allergic reactions. This is largely due to the formation of para-aminobenzoic acid (PABA) as a metabolite, which can trigger hypersensitivity in some individuals. Cocaine, while used primarily in specific medical contexts, is also an ester and carries the same risks associated with allergic reactions. Bupivacaine, on the other hand, while an amide like lidocaine, can still provoke allergic reactions in certain individuals, albeit with lower incidence compared to ester local anesthetics.

Therefore, lidocaine’s classification as an amide and its lower association with allergic reactions supports its position as the least likely local anesthetic to cause such reactions among the choices provided.