Gentamicin - Side Effects

Side Effects

These aminoglycosides are toxic to the sensory cells of the ear, but they vary greatly in their relative effects on hearing versus balance. Gentamicin is a vestibulotoxin, and can cause permanent loss of equilibrioception, caused by damage to the vestibular apparatus of the inner ear, usually if taken at high doses or for prolonged periods of time, but there are well documented cases in which gentamicin completely destroyed the vestibular apparatus after three to five days. A small number of affected individuals have a normally harmless mutation in their mitochondrial RNA (m1555 A>G), that allows the gentamicin to affect their cells. The cells of the ear are particularly sensitive to this, sometimes causing complete hearing loss. However, gentamicin is sometimes used intentionally for this purpose in severe Ménière's disease, to disable the vestibular apparatus. These side effects are most common when the drug is administered via drops directly to the eye.

Gentamicin can also be highly nephrotoxic, particularly if multiple doses accumulate over a course of treatment. For this reason gentamicin is usually dosed by body weight. Various formulae exist for calculating gentamicin dosage. Also trough and peak serum levels of gentamicin are monitored during treatment, generally before and after the third dose is infused.

Gentamicin, like other aminoglycosides, causes nephrotoxicity by inhibiting protein synthesis in renal cells. This mechanism specifically causes necrosis of cells in the proximal tubule, resulting in acute tubular necrosis which can lead to acute renal failure.

Side effects of gentamicin toxicity vary from patient to patient. Side effects may become apparent shortly after or up to months after gentamicin is administered. Symptoms of gentamicin toxicity include:

• Balance difficulty
• Bouncing, unsteady vision
• Ringing in the ears (tinnitus)
• Difficulty multi-tasking, particularly when standing

Psychiatric symptoms related to gentamicin can occur. These include anorexia, confusion, depression, disorientation and visual hallucinations. Immediate professional help should be sought if any of these symptoms or others appear after administration of aminoglycosides. General medical practitioners should refer patients with such symptoms to an otolaryngologist, commonly known as an 'ear, nose, and throat doctor', for comprehensive tests.

A number of factors and determinants should be taken into account when using gentamicin, including differentiation between empirical and directed therapy which will affect dosage and treatment period. Many medical practitioners freely administer gentamicin as an antibiotic without advising patients of the severe and permanent potential ramifications of its use. Gentamicin is well known to be a cheap, low-cost yet old medicine when compared with modern alternatives, and is typically US$3–6 per dosage less than modern alternatives.

Many people recover from gentamicin toxicity naturally over time if the drug is discontinued, but they recover slowly and usually incompletely. Sometimes the toxicity of gentamicin can still increase over months after the last dose. Upon cessation of gentamicin therapy symptoms such as tinnitus and imbalance may become less pronounced. Sensori-neural hearing loss caused by gentamicin toxicity is permanent however.