Although their influences on ECoG or morphology of the cochlea following general administration of aminogricosides were extensively studied in the past, the comprehensive studies on the changes of ECoG with the morphological characteristics after topical administration of the drugs into the tympanic cavity were limited. Thirty six guinea pigs were treated with topical administration of the drugs into the tympanic cavity through a tube which has been inserted and fixed operatively on the retroauricular portion. These drugs were composed of Gentamicin (GM) in a dose of 8 mg/day, Sisomicin (SISO) 10 mg/day, Cefsulodin (CFS) 20 mg/day and Cefmenoxime (CMX) 2 mg/day respectively. And, ECoG examination and the electron microscopic study for these animals were performed at pre- and post-treatment days. It was revealed that the ototoxicity of SISO and GM were observed functionally and morphologically in an almost same manner. On the other hand no ototoxicity of CFS and CMX were found. From the results which has been thus obtained, clinical significance and usefulness of the topical administration into the tympanic cavity of some antibiotics were discussed briefly.
