Pharmacology · Other antibacterials
Rifaximin !
A rifamycin that is barely absorbed, so it acts inside the gut: hepatic encephalopathy, traveller's diarrhoea and IBS with diarrhoea.
Updated 2026-11-01
The figure shows rifampicin, a close rifamycin relative that occupies the same pocket, bound to RNA polymerase of Thermus aquaticus.
Mechanism of action
Rifaximin binds the β subunit of bacterial DNA-dependent RNA polymerase and blocks the growing RNA chain, so transcription stops. Because almost none is absorbed, it stays in the intestine and reduces gut bacteria, including those that make ammonia and other toxins in liver disease.
- Stays in the gut lumen after an oral dose
- Binds the β subunit of bacterial RNA polymerase
- RNA synthesis is blocked
- Gut bacteria and their toxins decrease
Pharmacokinetics
- Absorption
- Very low, with or without food.
- Elimination
- Almost entirely in the faeces as unchanged drug.
Indications
- Reducing the risk of hepatic encephalopathy in cirrhosis Cirrhosis →
- Irritable bowel syndrome with diarrhoea Irritable bowel syndrome →
- Traveller's diarrhoea caused by non-invasive bacteria (not bloody diarrhoea or diarrhoea with fever)
Adverse effects
Common
- Nausea, stomach pain and dizziness
- Tiredness and headache
- Muscle tightness and joint pain
Contraindications
- Allergy to rifaximin
- Diarrhoea with fever or blood
Key interactions
- Other drugs
- Few interactions, because so little reaches the blood.
What is monitored
- Mental status in hepatic encephalopathy
- Stool pattern
- Persistence of diarrhoea beyond a few days
Administration and safety
- Taken by mouth, with or without food
- Not a treatment for bloody diarrhoea or diarrhoea with fever
Nursing care
- Teach the family the early signs of encephalopathy (confusion, sleep changes)
- Teach to report bloody stools or fever
- Check that lactulose or other measures continue as prescribed
Pregnancy and breastfeeding
Human data are limited; pregnancy is discussed before use.
Test yourself
Think of the answer, then tap the question to see it.
Why does rifaximin act mainly in the gut?
It is barely absorbed and is excreted unchanged in the faeces.
What is its target?
The β subunit of bacterial DNA-dependent RNA polymerase.
Which traveller's diarrhoea should not be treated with rifaximin?
Diarrhoea with blood or fever (invasive infection).
Related drugs
Related conditions
← Back to the class: Other antibacterials
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Rifaximin: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); Rifaximin (PubChem (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); Taq RNA polymerase-rifampicin complex (RCSB Protein Data Bank, 2026).
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Representative model, for educational purposes only.