Cytotoxicity of Ear Drop Excipients in Human and Mouse Tympanic Membrane Fibroblasts
Carolyn O. Dirain, PhD, David N. Karnani, Patrick J. Antonelli, MDFirst Published December 3, 2019 Research Article
https://doi.org/10.1177/0194599819889701
Article information
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Abstract
Objective
Commercial ear drops contain ingredients reported to be inactive. We sought to evaluate such excipients for possible cytotoxicity on human and mouse tympanic membrane (TM) fibroblasts.

Study Design
Prospective, in vitro.

Setting
Tertiary academic center.

Subjects and Methods
Mouse and human TM fibroblasts were treated with 1:10 dilutions of benzalkonium chloride (BKC) 0.0025%, 0.006%, or 0.01%; benzyl alcohol 0.9%; polysorbate 80 (PSB) 2.5%; glycerin 2.4%; povidone 0.2%; or water (control), twice within 24 hours or 4 times within 48 hours, for 2 hours each time. Cells were placed back in growth media after the treatments. Cells were observed with phase-contrast microscopy until the cytotoxicity assay was performed.

Results
Mouse fibroblasts had lower survival in only the PSB-treated cells compared to the control (P < .0001) after 24 hours. After 48 hours, PSB killed nearly all mouse fibroblasts (P < .0001). BKC decreased fibroblast survival in a dose-dependent manner (P < .001). In human TM fibroblasts, all excipients except povidone and benzyl alcohol after 24 hours and povidone after 48 hours reduced cell survival compared to control (P = .012 to P < .0001). The cytotoxicity of BKC in human TM fibroblasts was also dose dependent (<.0001). PSB was less cytotoxic to human fibroblasts. Phase-contrast images mirrored the cytotoxicity findings.

Conclusion
Polysorbate 80 and benzalkonium chloride, at concentrations found in commercial ear drops, may be cytotoxic to human and mouse TM fibroblasts. “Inactive” ingredients may need to be considered when evaluating clinical outcomes with commercial ear drops.

Keywords ear drops, excipients, tympanic membrane, fibroblasts, cytotoxicity