What is the mechanism of action for topical benzocaine anesthesia?

• A. It blocks potassium channels.
• B. It blocks voltage-gated sodium channels in mucosal membranes to numb the surface.
• C. It inhibits COX enzymes.
• D. It activates chloride channels.

Answer: (B)

Topical benzocaine produces numbness by blocking voltage-gated sodium channels on peripheral nerve membranes. Local anesthetics must cross the nerve membrane in their nonionized form and then inside the neuron bind to the sodium channel, stabilizing it in a non-conducting state. This prevents sodium influx during depolarization, halting action potential propagation and resulting in loss of sensation on the mucosal surface. The rapid surface effect seen with benzocaine reflects its topical use on mucosa, focusing the action on these superficial nerve endings. Other mechanisms, like blocking potassium channels, inhibiting COX enzymes, or activating chloride channels, do not explain how a local anesthetic ceases nerve signaling.