Late effects of topical anesthetics on the healing of guinea pig tympanic membranes after myringotomy

Background: The optimal local anesthetic for myrin-gotomies or the insertio n of tympanostomy tubes in adults should be easy and rapid to use, be painl ess during ap plication, provide good anesthesia, be reversible, be inexpen sive, and not cause any long-term damage to the tympanic membrane (TM). Objective: To evaluate the histologic effects of topical anesthetic agents on the healing of the TM after myringotomy. Methods: Sixty male albino guinea pigs were randomly assigned to 1 of 5 gro ups. Of the 5 groups, 2 were used as controls: one group underwent a myring otomy and the other group did not. The remaining 3 groups had both TMs trea ted with a topical anesthetic (phenol, tetracaine base, and eutectic mixtur e of lidocaine and prilocaine in a cream) prior to myringotomy. All TMs wer e inspected periodically and then harvested at 3 months or 6 months postope ratively for histologic examination. Results: The TMs of the group treated with tetracaine appeared the most nor mal at 6 months (P=.001). However, histologic evaluation failed to demonstr ate any significant differences in the thickness of the TM or the lamina pr opria (P=.45), the amount (P=.80) and orientation (P=.07) of collagen, or t he number of infiltrating lymphocytes (P=.70). Conclusion: Based on the histologic findings, all 3 topical anesthetic agen ts appear to cause equivalent changes to the TM when used for a myringotomy .