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

OBJECTIVES/HYPOTHESIS: To determine whether betamethasone (BM) reduces the cochlear toxicity of otic gentamicin (GM) if given together. STUDY DESIGN: Controlled animal study. METHODS: Thirty-four mice were assigned at random to receive intratympanic injections of either 0.1 % BM (11 mice), 0.3% GM (13 mice), or a combination of both (GM/BM) with benzalkonium chloride (10 mice) in the left ear (treated) and saline on the right (untreated). Six injections were given on alternate days. Auditory brainstem response thresholds were assessed at 1 month, 2 months, and >2 months. RESULTS: There was a significantly greater degree of hearing loss in the BM-treated ears compared to the untreated ears (6.48 dB hearing loss, P = .007) and in the GM-treated ears compared to untreated ears (6.59 dB hearing loss, P = .010,). However, otic GM/BM and benzalkonium chloride did not cause significant additional hearing loss compared with the untreated ears (3.56 dB hearing loss, P = .242). CONCLUSIONS: Our data suggest that hearing loss caused by GM otic drops may be reduced by the inclusion of BM and benzalkonium chloride. Our finding that BM alone was associated with hearing loss suggests that the benzalkonium chloride may be the protective agent in combination otic drops.

End points for cisplatin ototoxicity.

INTRODUCTION: Hearing loss owing to ototoxicity in humans is usually presumed to be irreversible and stable. Most articles in the literature study the effects of ototoxic agents such as cisplatin only over a few days or weeks. This study focused on the recovery of hearing over several months in mice. The same treatment was applied to guinea pigs to determine whether there were significant differences in response between the two species. METHODS: Thirty-two mice and 37 guinea pigs were randomized to receive either saline or cisplatin (15 mg/kg). After this exposure, we performed auditory brainstem response (ABR) testing on the mice over 8 months and on the guinea pigs for 1 month. RESULTS: Hearing loss owing to cisplatin shows significant variability between and within species. In mice, hearing loss is maximal at about 17 dB during the third month after cisplatin administration but actually improves to the level attributable to presbyacusis. Guinea pigs, however, experience greater, approximately 25 dB hearing loss within a month of administration of the same dose of cisplatin, tested with the same protocol. CONCLUSION: In general, ototoxicity end points should be assessed more than 1 month after exposure for animals. Our observation that hearing loss is incomplete before 1 month in mice opens the possibility of studies for preventive treatment during that time.

Does sodium thiosulphate delay presbyacusis?

INTRODUCTION: This study compares the effects of sodium thiosulphate (STS) and normal saline on the prevention of hearing loss. SETTING: Animal research laboratory. METHODS: Sixteen mice were randomized to receive intraperitoneal injections of either normal saline or STS. Auditory brainstem response testing was used to determine baseline and posttreatment hearing thresholds over the course of 1 year. RESULTS: Compared with saline, treatment with STS resulted in a statistically significant improvement in click and pure-tone thresholds until the end of the year. CONCLUSION: STS can significantly delay hearing loss associated with age in this murine model.