Reversible hearing impairment related to quinine blood concentrations in guinea pigs.

The hearing ability was measured in anaesthetised guinea pigs by recording cochlear evoked potentials induced by standardised sound stimulation. The animals were given quinine intravenously and blood samples were withdrawn for assay of quinine. The shift in hearing threshold was closely related to the quinine blood concentration. The effect-concentration relationships were analysed according to the equation L = 10 (log k+a.log (s-b] which can be viewed as a special case of the Hill equation assuming that the stimulation (s) is of very low intensity compared to the stimulus at which half of the maximum response would be obtained and introducing an absolute limit for a stimulus at which no response is obtained.