Gentamicin works by binding to a site on the bacterial ribosome, causing the genetic code to be misread.
Like all aminoglycosides, gentamicin does not pass the gastro-intestinal tract, so it can only be given intravenously or intramuscularly.
Gentamicin can cause deafness in genetically susceptible individuals. These individuals have a normally harmless mutation in their DNA, that allows the gentamicin to affect their cells. The cells of the ear are particularly sensitive to this.
Gentamicin can also be highly nephrotoxic, particularly if multiple doses accumulate over a course of treatment. For his reason gentamicin is usually dosed by body weight. Various formulae exist for calculating gentamicin dosage. Also serum levels of gentamicin are monitored during treatment.