THE EFFECT OF GENTAMICIN AND FUROSEMIDE GIVEN IN COMBINATION ON COCHLEAR POTENTIALS IN THE GUINEA-PIG

Single doses of gentamicin and furosemide given in combination result in a rapid and profound loss of cochlear function. In this study, meas urement of three gross cochlear potentials (cochlear microphonics, com pound action potentials and the endocochlear potential) were carried o ut in order to determine the ototoxic sites of action of the drugs giv en in combination. The rapidity and severity of the cochlear deficit i s dose dependent and with the doses employed in this study (80 mg/kg g entamicin iv 80 mg/kg furosemide iv), complete loss of cochlear functi on is seen after about 72 hours. Twenty-four hours after iv administra tion of the drugs, significant increases in compound action potential thresholds between 6 and 32 kHz were seen. In contrast, over this freq uency range the generation of cochlear microphonics in response to sti mulus levels of 70 dB SPL appeared to be unaffected. The endocochlear potential remained unaffected at 24 and 72 hours after administration. These findings are taken as evidence that the primary site of ototoxi c action of the two drugs in combination may be at the level of the in ner hair cells and/or the afferent synapse.