Inhibition by astemizole of activity from the isolated semicircular canal

Since astemizole does not readily pass the blood-brain barrier, it was surprising that it was found useful in patients with chronic vertigo. We therefore speculated that the drug may reach the inner ear and act directly on the sensory cell-afferent nerve synapse. Mice, injected with tritiated astemizole and killed 17 hours later, showed the presence of the drug in the vestibular tissues. Nerve recordings were made from the isolated posterior semicircular canal of the frog. Both spontaneous and stimulated firing rates were obtained with artificial perilymph containing astemizole bathing the isolated canal preparation. Results showed that astemizole has a significant inhibitory effect on vestibular nerve activity at concentrations of 10(-7) mol/L and higher. The exact site of astemizole's inhibitory action is undetermined but is most likely at the hair cell-afferent nerve synapse.