The efficacy of topical anesthetics has been difficult to assess in man because no wholly satisfactory method of study has been available. A technique embodying electrical stimulation of the mucous membranes was devised which permitted a comparison to be made of effectiveness, duration of action, and potency of such drugs. Over 40 drugs said to be active topically were studied. Tetracaine, cocaine, dibucaine, lidocaine, dyclonine, and hexylcaine proved to be the most serviceable. A maximum concentration exists for each drug above which no further enhancement of activity is noted. The most serviceable drugs are the ones which clinical experience has shown to be the most toxic systemically. Vasoconstrictors, detergents, demulcents, and other nonanesthetic substances do not enhance or prolong the effects of topical anesthetics. The latent period is shortened as the maximum effective concentration is approached.
Adriani J, Zepernick R. Clinical Effectiveness of Drugs Used for Topical Anesthesia. JAMA. 1964;188(8):711-716. doi:10.1001/jama.1964.03060340009003