Objective method for differentiating between drug-induced vestibulotoxicity and cochleotoxicity.

Hypothesis: An objective direct method is proposed to differentiate between drug-induced functional vestibulotoxicity and cochleotoxicity.

Background: Many substances are ototoxic. Although there are objective methods to directly evaluate functional cochlear toxicity (auditory nerve brainstem responses [ABR]), it is more difficult to assess direct functional ototoxicity to the various vestibular end organs.

Methods: Short-latency vestibular evoked potentials (VsEP) from different vestibular end organs and ABR, were used to assess functional impairment of the vestibular and cochlear end organs caused by daily injections of the aminoglycoside amikacin (known to be preferentially cochleotoxic) in guinea pigs.

Results: There was no significant change in the various VsEPs. whereas ABR thresholds were elevated, confirming the selective functional cochleotoxicity previously reported, as evaluated by other (mainly nondirect) methods.

Conclusion: This study demonstrates the feasibility in general of using short-latency evoked potentials to evaluate functional cochleotoxicity and vestibulotoxicity of ototoxic drugs and to differentiate between them.