Gentamicin-induced sensorineural auditory loss in healthy adult horses.
Authors: Aleman Monica R, True Alexander, Scalco Rebeca, Crowe Chelsea M, Costa Lais R R, Chigerwe Munashe
Journal: Journal of veterinary internal medicine
Summary
# Gentamicin-induced Sensorineural Auditory Loss in Horses Aminoglycosides are well-established ototoxic agents in human medicine, yet their auditory effects in horses have remained unexplored until this investigation. Ten healthy adult horses received gentamicin sulphate at the standard clinical dose of 6.6 mg/kg intravenously for seven consecutive days, with auditory function assessed via brainstem auditory evoked responses (BAER) before treatment, immediately post-treatment, and 30 days later; bone conduction testing ruled out conductive hearing disorders. Seven of the ten horses (70%) developed sensorineural auditory loss, with presentations ranging from complete bilateral loss (one horse) through complete or partial unilateral loss (six horses combined), and crucially, four horses demonstrated reversible dysfunction whilst three retained permanent hearing deficits. This finding fundamentally challenges current assumptions about gentamicin safety in equine practice and warrants urgent reconsideration of aminoglycoside protocols; practitioners should discuss ototoxicity risk with clients before commencing treatment, consider alternative antimicrobials where possible, and recognise that even standard recommended dosing carries a substantial risk of irreversible hearing loss in a significant proportion of treated horses.
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Practical Takeaways
- •Gentamicin at standard recommended doses carries significant risk of hearing loss in horses; consider whether alternative antibiotics are appropriate before initiating treatment
- •If gentamicin is necessary, monitor horses for auditory changes and counsel owners that some hearing loss may be permanent despite standard dosing protocols
- •Baseline and post-treatment BAER testing should be considered in horses requiring extended gentamicin courses to detect auditory changes early, as reversibility was possible in some cases
Key Findings
- •70% of horses (7/10) treated with recommended IV gentamicin dosage (6.6 mg/kg daily for 7 days) developed sensorineural auditory loss
- •Auditory loss ranged from complete bilateral to partial unilateral, with 1 complete bilateral case, 2 complete unilateral cases, and 4 partial unilateral cases
- •Auditory dysfunction was reversible in 57% of affected horses (4/7) at 30-day follow-up, but 3 cases remained irreversible
- •Bone conduction testing confirmed sensorineural rather than conductive etiology in horses with absent BAER responses