Cytotoxicity of Tetracyclines in Human Tympanic Membrane Fibroblasts

Hypothesis Tetracyclines are less cytotoxic to tympanic membrane (TM) fibroblasts than quinolones. Background Use of quinolone ear drops after tympanostomy tube placement and for acute otitis externa has been linked to an increased risk of TM perforation. This has been verified in animal models. Cell culture studies have shown quinolones to be highly toxic to TM fibroblasts. Tetracyclines are a potential alternative to quinolones as they have been used to treat acute otitis externa and are thought to be nontoxic to the inner ear. We aimed to determine if tetracyclines are cytotoxic to TM fibroblasts. Methods Human TM fibroblasts were treated with 1:10 dilutions of ofloxacin 0.3%, ciprofloxacin 0.3%, doxycycline 0.3 and 0.5%, minocycline 0.3 and 0.5%, tetracycline 0.3 and 0.5%, or dilute HCl (control), twice within 24 hours or four times within 48 hours. After 2 hours of treatment, cells were returned to growth media. Cells were observed with phase-contrast microscopy until cytotoxicity was measured. Results Fibroblasts had lower survival with ciprofloxacin 0.3% and doxycycline 0.5% treatment compared with the control after 24 and 48 hours (all p < 0.0001). Fibroblasts treated with minocycline 0.5% had increased cell survival after 24 hours. Minocycline 0.3 and 0.5% showed increased TM fibroblast survival after 48 hours (all p < 0.0001). Phase-contrast images mirrored the cytotoxicity findings. Conclusions Tetracyclines are less toxic to cultured TM fibroblasts than ciprofloxacin. Fibroblast tetracycline toxicity is drug and dose specific. Minocycline shows the most promise for possible otic applications in which fibroblast toxicity is a concern.