Prevention of Noise-Induced Hearing Loss Using Investigational Medicines for the Inner Ear: Previous Trial Outcomes Should Inform Future Trial Design

Abstract

Significance. Noise-induced hearing loss (NIHL) is an important public health issue resulting in decreased quality of life for affected individuals and significant costs to employers and governmental agencies.Recent Advances. Advances in the mechanistic understanding of NIHL have prompted a growing number of proposed, in-progress, and completed clinical trials for possible protections against NIHL via antioxidants and other drug agents. Thirty-one clinical trials evaluating prevention of either temporary or permanent NIHL were identified and are reviewed.Critical Issues. This review revealed little consistency in the noise-exposed populations in which drugs are evaluated or the primary outcomes used to measure NIHL prevention.Changes in pure-tone thresholds were the most common primary outcome; specific threshold metrics included both average hearing loss and incidence of significant hearing loss. Changes in otoacoustic emission (OAE) amplitude were a relatively common secondary outcome. Extended high frequency (EHF) hearing and speech-in-noise perception are commonly adversely affected by noise exposure but are not consistently included in clinical trials assessing prevention of NIHL.Future Directions. Multiple criteria are available for monitoring NIHL, but the specific criterion to be used to define clinically significant otoprotection remains a topic of discussion. Audiogram-based primary outcome measures can be combined with secondary outcomes, including OAE amplitude, EHF hearing, speech-in-noise testing, tinnitus surveys, and patient-reported outcomes. Standardization of test protocols for the above primary and secondary outcomes, and associated reporting criterion for each, would facilitate clinical trial design and comparison of results across investigational drug agents.

Investigational Medicinal Products for the Inner Ear: Review of Clinical Trial Characteristics in ClinicalTrials.gov

“…Additional detailed discussion of the state of the science for NIHL otoprotection research based on both the peerreviewed literature and studies listed in ClinicalTrials.gov can be found in Le Prell. 130 Looking beyond the audiogram, DPOAEs were monitored in about 33% of the DIHL and 56% of the NIHL trials, but they were largely absent from stable SNHL and acute SSNHL clinical trials. In participants entering a clinical trial with significant hearing loss, as in many of the stable SNHL and acute SSNHL trials in ►Tables 3 and 4, DPOAEs likely have limited utility as they are expected to be compromised at enrollment and thus it is not surprising they were not included in the study test battery.…”

“…Additional detailed discussion of the state of the science for NIHL otoprotection research based on both the peer-reviewed literature and studies listed in ClinicalTrials.gov can be found in Le Prell. 130 …”