Safety of ciprofloxacin and dexamethasone in the guinea pig middle ear

To investigate the ototoxic potential of ciprofloxacin hydrochloride, 0.3%, plus dexamethasone, 0.1%, after administration to the guinea pig middle ear.

Fifty guinea pigs were randomly assigned to 4 test groups of 10 animals each and 2 control groups of 5 animals each. The 4 test groups were treated twice daily for 4 weeks with 10 muL of (1) ciprofloxacin hydrochloride, 0.3%, plus dexamethasone, 0.1%; (2) ciprofloxacin hydrochloride, 1.0%, plus dexamethasone, 0.3%; (3) ciprofloxacin hydrochloride, 0.3%, or (4) vehicle. The positive and negative control groups were treated with neomycin sulfate, 10%, or isotonic sodium chloride solution, respectively.

Academic research laboratory.

Study animals were implanted with a drug delivery cannula to the middle ear, terminating in the round window niche for direct delivery to the round window membrane.

Auditory brainstem responses were collected at baseline and following 2 and 4 weeks of dosing. At the termination of the study, inner ear tissues were evaluated microscopically.

No biologically relevant hearing losses were observed after either 2 or 4 weeks of treatment with vehicle, ciprofloxacin alone, or combinations of ciprofloxacin plus dexamethasone. Examination of the organ of Corti revealed normal hair cell counts in all animals that received isotonic sodium chloride solution, vehicle, ciprofloxacin, or combinations of ciprofloxacin and dexamethasone. Conversely, the neomycin sulfate positive control group demonstrated a significant elevation in hearing threshold and profound hair cell loss (P <.001, P = .02, and P <.001 at 2, 8, and 16 kHz, respectively).

The results of this preclinical study support the safety of ciprofloxacin hydrochloride, 0.3%, plus dexamethasone, 0.1%, for clinical use in the open middle ear cavity.