Decreased efficacy of topical anesthetic creams in presence of benzoyl peroxide.

Background: Topical anesthetics are widely used to diminish the sensation of pain from various medical cutaneous procedures. Any topical agent that reduces the desired effect has clinical ramifications.

Materials And Methods: Topical 6% benzocaine cream was applied to both inner forearms of five persons and covered with a bandage. One of the arms was additionally treated simultaneously with 5% benzoyl peroxide. The areas were tested with a pinprick examination every 10 minutes for the ensuing hour.

Results: There was an estimated 75% increased perception of pain on the forearm to which benzoyl peroxide was applied in consort with the topical anesthetic at all examination times.

Conclusions: Benzoyl peroxide chemically reacts with topical anesthetics such as tetracaine, procaine, pramoxine, prilocaine, and lidocaine, causing a significant reduction in their numbing effect. Clinically, make sure that the skin area to be topically anesthetized is devoid of any previous treatment with benzoyl peroxide or insist that the skin is thoroughly washed prior to application of the anesthetic.