Pharmacology · Class
Aminoglycosides !
Bactericidal antibiotics that make bacteria misread their genetic code; strong against aerobic gram-negatives but toxic to kidney and ear.
Updated 2026-11-01
What they are
A family of water-soluble sugar-based antibiotics (gentamicin, tobramycin, amikacin, streptomycin, neomycin, plazomicin). They are given by injection or inhalation, are used for serious aerobic gram-negative infections and, combined with a cell-wall drug, for some gram-positive endocarditis. Streptomycin and amikacin also treat mycobacterial infections.
Mechanism of action
They pass the outer membrane through porins and then cross the inner membrane by an oxygen-dependent transport, which is why anaerobes resist them. Inside, they bind the 16S rRNA of the 30S ribosomal subunit: they block the start of protein synthesis, cause misreading of the mRNA and premature stops. Faulty proteins inserted into the membrane let even more drug in. Killing depends on the peak concentration, and the effect lasts after levels fall (postantibiotic effect).
Target: 16S rRNA of the bacterial 30S ribosomal subunit
Drugs in this class
- GentamicinThe workhorse injectable aminoglycoside for serious gram-negative infections and, with penicillin, for some…Decoding (A) site of the bacterial 16S rRNA, 30S ribosomal subunit
- AmikacinA semisynthetic aminoglycoside that resists most bacterial inactivating enzymes; used for resistant gram-negatives and…Decoding (A) site of the bacterial 16S rRNA, 30S ribosomal subunit
- TobramycinAn aminoglycoside close to gentamicin but more active against Pseudomonas aeruginosa; injected, or inhaled in cystic…Decoding (A) site of the bacterial 16S rRNA, 30S ribosomal subunit
- StreptomycinThe first aminoglycoside; given intramuscularly for tuberculosis, plague, tularemia and brucellosis. It damages…16S rRNA and ribosomal protein S12 of the bacterial 30S subunit
- PlazomicinA newer aminoglycoside built to resist modifying enzymes; used for complicated urinary infections, including…Decoding (A) site of the bacterial 16S rRNA, 30S ribosomal subunit
- NeomycinAn aminoglycoside used by mouth to suppress gut bacteria (bowel preparation, hepatic encephalopathy) and on the skin…Decoding (A) site of the bacterial 16S rRNA, 30S ribosomal subunit
Others in the class
- kanamycin
- netilmicin
- paromomycin
Test yourself
Think of the answer, then tap the question to see it.
Why are aminoglycosides inactive against Bacteroides fragilis and other anaerobes?
Their transport across the bacterial inner membrane needs oxygen-dependent electron transport, which strict anaerobes lack.
What are the three classic toxicities of aminoglycosides?
Nephrotoxicity, ototoxicity (hearing and balance) and neuromuscular blockade, which can cause apnea after anaesthesia or in myasthenia gravis.
Why can an aminoglycoside be given once a day despite a short half-life?
Killing rises with the peak level and the postantibiotic effect keeps suppressing growth after levels fall below the MIC.
Which part of the ribosome do aminoglycosides bind?
The 16S rRNA of the 30S subunit, at the decoding (A) site, which causes mRNA misreading.
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 59 (McGraw Hill, 2023); DailyMed - GENTAMICIN SULFATE injection, solution (DailyMed (U.S. National Library of Medicine), 2026); DailyMed - AMIKACIN SULFATE injection, solution (DailyMed (U.S. National Library of Medicine), 2026).
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Representative model, for educational purposes only.