Gentamicin is an aminoglycoside antibiotic, and can treat many types of bacterial infections, particularly Gram-negative infection. However, gentamicin is not used for Neisseria gonorrheae, Neisseria meningitidis or Legionella pneumophila infections.
Gentamicin is a bactericidal antibiotic that works by binding the 30S subunit of the bacterial ribosome, interrupting protein synthesis.
Like all aminoglycosides, when gentamicin is given orally, it is not effective. This is because it is absorbed from the small intestine, and then travels through the portal vein to the liver, where it is inactivated. Therefore, it can only be given intravenously, intramuscularly or topically.
All 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 usually cause permanent loss of equilibrioception, caused by damage to the vestibular apparatus of the inner ear if taken more than a few times. Gentamicin has on occasion impaired or even wholly destroyed hearing and effects kidney function. In most instances, the affected individual has undergone treatment for 2 weeks or more. A small number of affected individuals have a normally harmless mutation in their mitochondrial RNA, that allows the gentamicin to affect their cells. The cells of the ear are particularly sensitive to this. Gentamicin is sometimes used intentionally for this purpose in severe Ménière’s disease, to disable the vestibular apparatus.
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 serum levels of gentamicin are monitored during treatment.