Final answer:
Benzocaine is contraindicated for patients with PABA allergies because it is a PABA ester, unlike lidocaine and prilocaine, which are amide-type anesthetics and not related to PABA.
Step-by-step explanation:
Topical benzocaine is contraindicated for patients who are allergic to para-aminobenzoic acid (PABA). This is because benzocaine is a para-aminobenzoic acid ester and can cause allergic reactions in individuals with an allergy to PABA. Local anesthetics like benzocaine, lidocaine, EMLA (which contains lidocaine and prilocaine) and prilocaine, work by blocking sodium channels and thus prevent sodium from moving across the neuronal membrane. This blocking action stops the propagation of the nerve impulse, leading to reversible loss of sensation in the applied area. While prilocaine and lidocaine are amide-type anesthetics and generally do not cause allergic reactions related to PABA, it is benzocaine which is related to PABA and should be avoided by patients with known PABA allergies.