A Review of Animal Studies for the Efficacy of D-Methionine in Reducing Threshold Shifts and Affecting Biochemical Changes after Exposure to Noise

Noise induced hearing loss (NIHL) is a major public health concern in the United States and worldwide. Certain individuals such as factory workers and military personnel are at greatest risk for irreversible sensorineural hearing loss due to the limitations of hearing protection measures and devices. D-Methionine (d-Met) is an antioxidant otoprotective agent that currently is in human clinical trials. The purpose of this systematic literature review was to review d-Met’s efficacy in reducing threshold shifts as well as in producing biochemical and physical changes in animal studies vis-à-vis the administration paradigm (preloading, rescue and a combined approach), d-Met dose quantity and the number and schedule of administrations. The results revealed that d-Met is efficacious across administration paradigms and dosing strategies. A consensus regarding an optimal dose amount or schedule of administration was not found in the studies reviewed. Clinical utility for the pre-loading paradigm exists in the opportunity to utilize d-Met as a prophylactic otoprotective agent. A rescue paradigm similarly provides clinical utility, offering a way to recover NIHL in cases where noise exposure is unforeseen