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Tim Boysen's Gentamicin observations

  • (Copied over from our old MM.org archives for database reference)

    I believe Gentamicin is the best option for some Meniere's patients. Since 1948, aminoglycosides have been used to selectively destroy the vestibular hair cells in an ear (or ears) that produce unrelenting, disabling vertigo. Maybe 10% of Meniere's patients end up in that state. In the 47 years of experimentation and treatment several things have been learned and the procedures have been steadily refined. For a patient facing general anesthesia and neurosurgery (with risks of paralysis or encephalitis) to obliterate the inner ear, gentamicin treatment can be a godsend.

    A few things that have been learned:
    • The ototoxic drug destroys the vestibular hair cells (the neural sensory cells) before (at lower doses) it destroys the auditory hair cells. With carefully controlled doses spaced over days or administered continuously over days or weeks, damage to the hearing function can be almost totally avoided and damage to the vestibular hair cells can be stopped as soon as vertigo is controlled.

    • As is the case with many instances in neurosurgery, the staged application of the drug over a long period while the patient remains active appears to allow the central nervous system to "recalibrate" fairly well and avoid significant balance problems or visual fixation/stabilixzation problems. The alternative--surgery--cannot provide this important advantage. In fact, many patients who have severe Meniere's and end up having both vestibular systems destroyed or disconnected by surgery end up fully disabled. With current methods of bilateral ototoxic vestibular ablation the patient is able to move around essentially normally.

    • It has been documented in the past few years, that the gentamicin also destroys or changes part of the "dark cells" in the inner ear. These cells appear to be responsible for control of ionic balances within the inner ear and the production of endolymph. In Meniere's disease, the dark cells are suspect. They may be the root cause of at least some cases. Gentamicin has been shown to reduce production of endolymph in healthy guinea pigs. Whether gentamicin can reduce the endolymphatic hydrops that is believed to be responsible for the symptoms and progression of Meniere's is not yet known, but data showing hearing preservation show that it may work that way in some cases.

    • There is evidence that gentamicin in low doses can preserve hearing. Not all studies show this result and researchers are trying to determine how the different treatments/protocols vary in this regard. Some large studies have shown hearing stabilization of over 90%, others have shown no hearing stabilization at all. The assumption is that gentamicin selectively destroys the endolymph-production capacity of the inner ear, resulting in better ionic (salt) balance in the fluid and lowered pressure.
    Let me add that the most ototoxic thing in Meniere's disease is the endolymph that is overproduced in part of the cochlea. This fluid appears to leak and enter the perilymph and contact both vestibular and auditory hair cells which it then poisons. Introduction of the right amount of the "ototoxic" gentamicin can--maybe--stop this natural ototoxic process.

    Thanks to Jim Chinnis for this explanation.
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