Alterations in ABR thresholds after drug-eluting electrode insertion. ABR thresholds at 4, 8 and 16 kHz were obtained before, immediately after surgery and repeated for 4 weeks until the end of the treatment (n = 5 per group). Graphs show ABR thresholds in decibels (mean ± SD) of average of three frequencies (4, 8, and 16 kHz). Repeated measures ANOVA of average ABR thresholds revealed significant differences between non-coated (gel (−)) and IGF1- (gel (+) IGF1) or HGF-adsorbed (gel (+) HGF) hydrogel electrodes (*P < 0.05). Hydrogel-coated electrode without medication (gel (+)) showed superior protective effect over bare electrode. In individual frequency analyses at 4, 8, or 16 kHz, IGF1 or HGF electrode showed significant attenuation of hearing loss after surgery, whereas IGF plus HGF electrode showed significant differences only at 16 kHz. Gel (+) electrode showed significant hearing loss-reducing effect until 2 weeks after surgery in analyses using 4 kHz ABR thresholds (**P < 0.025).