Topical Anaesthesia of the Normal Tympanic Membrane: A Controlled Clinical Trial of Different Suspensions of Lidocaine

The purpose of this investigation was to find an effective method for topical lidocaine anaesthesia of the tympanic membrane for minor therapeutical procedures. Twelve subjects with healthy ears were tested in a randomized double-blind crossover trial. Xylocaine (lidocaine) aerosol 10%, lidocaine 4%, and lidocaine hydrochloride 5% were tested against placebo. Xylocaine aerosol was sprayed into a small container, shaken, and tempered. This made the application painless. The eardrum was stimulated by a point of a needle effective 25 min after application (p = 0.008 and p less than 0.05, respectively). Lidocaine hydrochloride showed no effect. No side effects were observed. The effectiveness seems to be dependent on the ionization of the drug, since the two effective drugs lidocaine and Xylocaine are un-ionized, whereas the ineffective lidocaine hydrochloride is ionized.