There's not much in the literature about the toxicity of ear packs using the ingredients in Oti-Pak E and BNT. Most of the issues are with the use of gentamicin, which is not in these particular products. However, I did find the following warnings about the use of ear packs in general:
(1) If the ear drum is broken, then drugs that would not normally cause deafness can flow into the middle ear and cause deafness:
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The most severe signs of ototoxicity become apparent when the ear drum is damaged and the barrier between the external ear canal and middle and inner ear is breached. This allows topical medication to enter the middle ear which can lead to profound damage. It is thus crucially important when deciding on therapy for ear disease that the clinician is able to examine the ear canal and the ear drum effectively. When it is impossible to visualize the tympanum it is safest to assume it is ruptured. If the tympanic membrane is intact then the risks of causing damage to the ear are reduced.
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from
https://www.cabdirect.org/cabdirect/...0073120055.pdf (OTOTOXICITY – WHAT TO CHOOSE WHEN YOU HAVE TO USE SOMETHING? by Sue Patterson. North American Veterinary Conference, 2007.)
(2) Ear packs can cause toxic substances released by yeast and bacteria to remain in contact with the lining of the ear, causing damage:
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Use ear packings of topical drugs cautiously; they maintain cytopathic enzymes in contact with the ear canal longer.
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from
https://www.cliniciansbrief.com/site...tisExterna.pdf (Otitis Externa, by Louis Gotthelf, DVM, Montgomery, AL)