The ototoxic potential of propylene glycol in guinea pigs.

Propylene glycol, previously indicated to be ototoxic and to produce "deafness," was studied in the middle ear space of guinea pigs. Ninety percent propylene glycol produced conductive middle ear problems, but there was no loss of hair cells above that found in normal untreated animals. Ten percent propylene glycol produced no negative effects in the middle ear or elsewhere. Topical ear drops containing high concentrations of propylene glycol are contraindicated in cases with perforation of the tympanic membrane.