Gentamicin

Gentamicin is a mixture of closely related aminoglycosides made by Micromonospora purpurea. It binds the 30S ribosomal subunit, causes misreading of mRNA and kills Pseudomonas, E. coli, Klebsiella and staphylococci. Streptococci and enterococci resist it on its own, but with a penicillin it kills them synergistically. It is not metabolized and leaves unchanged in the urine.

Like other aminoglycosides: Aminoglycosides bind the 16S rRNA of the bacterial 30S ribosomal subunit, so the ribosome misreads mRNA and builds faulty proteins, and the bacteria die. Killing grows with peak concentration and goes on after levels fall (a post-antibiotic effect), which suits once-daily dosing. Anaerobes resist them, and with a cell wall agent such as a penicillin they act synergistically.

• Peak and trough levels guide dosing; a high trough signals accumulation and a higher risk of kidney and ear damage.
• Doses follow kidney function; older people, newborns, obesity, dehydration and long courses all need closer monitoring.
• Avoid with furosemide, other aminoglycosides, vancomycin, cisplatin, amphotericin B or ciclosporin, which add ear or kidney damage.
• UK labels contraindicate it in myasthenia gravis; in surgery it can prolong the block from curare-type muscle relaxants.

Good to know: WHO lists it, like ampicillin and benzylpenicillin, as a first-choice Access antibiotic for sepsis in newborns and children, and as a second choice for gonorrhea.

Easily mixed up with tetracyclines and glycopeptides.