Pharmacology · Class
Other antibacterials !
Antibacterials that fit no larger family: chloramphenicol, rifaximin and spectinomycin, each with a narrow but important role.
Updated 2026-11-01
What they are
A grouping for single drugs from different chemical families. Chloramphenicol is a broad-spectrum 50S inhibitor kept for serious infections when safer drugs cannot be used; rifaximin is a rifamycin that stays in the gut; spectinomycin is an injectable 30S inhibitor for gonorrhoea.
Mechanism of action
Chloramphenicol blocks the peptidyl transferase centre of the 50S subunit; spectinomycin binds the 30S subunit and blocks translocation; rifaximin binds the β subunit of bacterial RNA polymerase and stops transcription, acting almost only inside the intestine because it is barely absorbed.
Target: Bacterial ribosome (chloramphenicol, spectinomycin) or RNA polymerase (rifaximin)
Drugs in this class
- ChloramphenicolAn old broad-spectrum antibiotic kept for serious infections when safer drugs fail, because it can destroy the bone…Bacterial ribosome, 50S subunit (peptidyl transferase centre)
- RifaximinA rifamycin that is barely absorbed, so it acts inside the gut: hepatic encephalopathy, traveller's diarrhoea and IBS…Bacterial DNA-dependent RNA polymerase, β subunit
- SpectinomycinAn injectable aminocyclitol that binds the 30S ribosome. A WHO second-choice drug for gonorrhoea when first-line…Bacterial ribosome, 30S subunit
Test yourself
Think of the answer, then tap the question to see it.
What is grey baby syndrome?
Chloramphenicol toxicity in newborns, who cannot yet clear the drug well: abdominal distension, vomiting, pallid cyanosis and circulatory collapse.
Why does rifaximin act mainly in the gut?
It is very poorly absorbed, so almost all of it stays in the intestinal lumen and leaves in the faeces.
For which infection is spectinomycin used?
Gonorrhoea, as a second-choice injectable drug.
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - CHLORAMPHENICOL SODIUM SUCCINATE- chloramphenicol sodium succinate injection, powder, lyophilized, for solution (DailyMed (U.S. National Library of Medicine), 2026); Rifaximin: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); eEML - Electronic Essential Medicines List (World Health Organization, 2025).
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Representative model, for educational purposes only.