“ARO: The Sound of Safety: Why Glp Ototoxicity Testing Must Be Standard." Ellie Khadir, Gaëlle Naert, Marie-Pierre Pasdelou, Aurore Marie, Rami Tzafriri, Donald Hodges
Background: Hearing loss affects approximately 1.5 billion people worldwide, with ototoxicity representing a leading cause of acquired hearing loss globally. The number of ototoxic drugs is estimated between 150-600, with over 200 marketed medications documented to cause ototoxicity. While FDA guidelines define otic assessments for drugs delivered directly to the ear, testing for systemically administered therapies remains optional, leaving critical regulatory gaps despite the potentially devastating consequences of auditory dysfunction.
Methods: Current FDA regulations for Good Laboratory Practices (GLP) (21 CFR Part 58) govern nonclinical studies, with guidance for otic administration specifying auditory brainstem response (ABR) and cochleogram as primary endpoints. However, for systemically administered therapies, no dedicated guidance exists, leaving assessments to case-by-case evaluations and underscoring the need for transparent dialogue between sponsors and regulatory authorities. Study designs utilize 10 animals per sex per group with preferred species including rats (Wistars in Europe and Sprague Dawley in North America), CBA/CaJ mice (age-stable hearing characteristics), and Hartley guinea pigs (enhanced ototoxic sensitivity). Three doses are tested: low (pharmacological), intermediate, and high, with reversibility periods to assess effect permanence. Key assessment methods include ABR measuring cochlear and neural pathway functionality through synchronous neuronal discharge; and cochleogram providing histological assessment of hair cell loss across 4 rows. In addition, DPOAE, electroacoustic measure, assessing outer hair cell integrity through acoustic signals from cochlear epithelium can be performed. ; Clinical interpretation follows ASHA criteria defining significant hearing change as ≥20 dB decline at any frequency or ≥10 dB decline at two adjacent frequencies. Key components of GLP include an effective quality assurance program, proper management and staff training, adequate facilities and equipment, clear and documented procedures, and meticulous record-keeping to provide traceability and reproducibility of study results, with compliance ensured via regulatory agency audits and inspections.
Results: Preclinical data demonstrate that small threshold shifts (5-10 dB) without histopathological changes may represent normal test-retest variability, requiring integrated interpretation of ABR, DPOAE, and cochleogram findings. Therapy-specific study designs include: small molecules utilizing standard repeated-dose protocols with functional testing at baseline, interim, and terminal timepoints; gene therapy requiring specialized round window/cochleostomy injection with 3-6 month observation periods and biodistribution studies; cell therapy employing local delivery approaches with engraftment monitoring and immune response evaluation; local delivery necessitating trans-tympanic or intracochlear routes demanding specialized surgical expertise
Conclusions: Ototoxicity assessment is established for local otic administration but remains optional for systemic dosing, reflecting on regulatory gaps. Comprehensive evaluation requires integration of electrophysiological and histological expertise and, for otic delivery, surgical proficiency,. Given the devastating impact of auditory dysfunction and the absence of formal regulatory requirements, incorporating ototoxicity testing into standard GLP safety guidelines would enable earlier detection of auditory risk, prevent irreversible hearing loss, and strengthen the evidence base for therapeutic decision-making.