Quantitative assessment of torasemide ototoxicity.

Torasemide (1-isopropyl-3- ([4-(3-methyl-phenylamino)pyridine]-3-sulfonyl)urea), a new loop diuretic, was quantitatively tested for ototoxicity in cats. The toxic dose that causes a defined hearing loss in 50% of the animals (TD50) was determined. TD50 was calculated as 20.8 mg/kg. This is slightly but not significantly above the value for furosemide (18.37 mg/kg). Hearing function tended to recover after the acute effect. The main metabolite in man (1-isopropyl-3-([(3-carboxy-anilino)-3-pyridyl]sulfonyl)urea, M5) showed no ototoxic action even in excessive doses. To ensure complete recovery, hearing function was tested in animals pretreated with torasemide in doses higher than TD50. There was no indication for permanent hearing impairment in these pretreated animals.