Effects of nimodipine on quinine ototoxicity.

The compound action potential (CAP) in response to a click train stimulus was recorded at the round window of guinea pigs. Administration of quinine hydrochloride (200 mg/kg) significantly elevated the CAP thresholds by 5 to 25 dB (p < .05), and the CAP waveform elicited by the click train stimulus was abnormal. The amplitude of the CAP elicited by the second click was bigger than that elicited by the first click. These changes may be caused by an abnormally broadened N1 response to the first click in the click train. In contrast, CAP waveforms elicited by the second and subsequent clicks appeared normal. After administration of nimodipine (2 mg/kg), the CAP thresholds and waveforms elicited by the click train stimulus were unchanged. Simultaneous administration of both quinine (200 mg/kg) and nimodipine (2 mg/kg) resulted in the same electrophysiological changes as those induced by quinine alone. These results suggest that nimodipine prevents neither the deterioration in the CAP nor the abnormal properties in the response to a click train stimulus.