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[Pharmacology](https://durgical.com/en/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)

## Key points

- Chloramphenicol: dose-related marrow suppression and rare, irreversible aplastic anaemia; grey baby syndrome in newborns.
- Rifaximin is barely absorbed, so it works in the gut lumen: hepatic encephalopathy, traveller's diarrhoea and irritable bowel syndrome with diarrhoea.
- Spectinomycin is a WHO second-choice drug for gonococcal infection.
- Chloramphenicol remains on the WHO list as a second choice for bacterial meningitis where other drugs are not available.

## Drugs in this class

- [**Chloramphenicol** An 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)](https://durgical.com/en/pharmacology/chloramphenicol/)
- [**Rifaximin** A 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](https://durgical.com/en/pharmacology/rifaximin/)
- [**Spectinomycin** An injectable aminocyclitol that binds the 30S ribosome. A WHO second-choice drug for gonorrhoea when first-line… Bacterial ribosome, 30S subunit](https://durgical.com/en/pharmacology/spectinomycin/)

## 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.

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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](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=aed29594-211d-49ef-813f-131975a8d0e3) (DailyMed (U.S. National Library of Medicine), 2026); [Rifaximin: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a604027.html) (MedlinePlus (U.S. National Library of Medicine), 2026); [eEML - Electronic Essential Medicines List](https://list.essentialmeds.org/?query=spectinomycin) (World Health Organization, 2025).

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/classes/other-antibacterials/