The ototoxicity of chloroquine sulphate in the guinea pig

Chloroquine has been implicated as a possible ototoxic agent. The aim of this study was to investigate whether treatment with chloroquine sulphate causes permanent damage to the sensory hair cells of the spiral organ in the guinea pig. Both albino and pigmented animals were given seven daily subcutaneous injections of either 80 mg/kg or 60 mg/kg of the drug or the equivalent volume of normal saline to act as controls. The animals were killed 21 days after the final injection, and the cochleae prepared for examination under light microscopy using the surface specimen technique. The spiral organ was assessed in segments each of 100 outer hair cells in length and the percentage of damaged inner and outer hair cells for each segment was calculated. Chloroquine sulphate was found to be highly toxic when administered in single doses in excess of 40 mg/kg. No evidence was found to suggest that chloroquine causes permanent damage to the hair cells. The affinity of chloroquine for melanin and the possible effects on its ototoxicity are discussed.