Distribution of labeled chloroquine in the inner ear.

Autoradiography of the inner ear was performed at varying intervals following intravenous injection of either chloroquine tagged with carbon 14 (14C), or an iodine 125 (125l)-labeled analogue of chloroquine, in rats. In pigmented rats a strong accumulation and retention was noted in the melanin-bearing tissues. In the inner ear there was a very high concentration in the melanin-containing tissues, eg, the stria vascularis and the planum semilunatum. A strong retention was found in these structures 13 days after injection. Accumulation was not observed in the endolymph nor in the perilymph. No accumulation was found in the inner ear of an albino rat. The ototoxic effects of chloroquine may be caused by an accumulation of the drug in the melanin-containing structures in the inner ear, leading to pathological changes in these tissues and secondary lesions in the receptor cells.