Steroids in aminoglycoside-containing ear drops: do they reduce cochlear toxicity?

Area of Science:

• Ototoxicity research
• Pharmacology of otic preparations
• Auditory neurophysiology

Background:

• Otic gentamicin (GM) can cause cochlear toxicity and hearing loss.
• Betamethasone (BM) is a corticosteroid with anti-inflammatory properties.
• The potential protective effects of BM and other agents against GM-induced ototoxicity are not fully understood.

Purpose of the Study:

• To investigate whether betamethasone (BM) reduces the cochlear toxicity of otic gentamicin (GM) when administered concurrently.
• To evaluate the role of benzalkonium chloride in combination otic drops.

Main Methods:

• A controlled animal study involving 34 mice.
• Mice received intratympanic injections of BM, GM, or a combination of GM/BM with benzalkonium chloride in one ear and saline in the contralateral ear.
• Auditory brainstem response thresholds were assessed at multiple time points post-injection.

Main Results:

• Both BM and GM alone caused significant hearing loss compared to untreated ears.
• The combination of otic GM/BM with benzalkonium chloride did not result in significant additional hearing loss compared to untreated ears.
• Hearing loss in BM-treated ears was comparable to that in GM-treated ears.

Conclusions:

• The co-administration of betamethasone (BM) and benzalkonium chloride may reduce hearing loss induced by otic gentamicin (GM).
• The findings suggest that benzalkonium chloride, not BM, might be the primary protective agent in combination otic drops.
• Further research is warranted to elucidate the protective mechanisms of benzalkonium chloride in otic formulations.