Pharmacology · Mucosal protectants (sucralfate and bismuth)
Bismuth subsalicylate !
A bismuth salt for diarrhoea and upset stomach, and part of quadruple therapy for H. pylori. It turns the tongue and stools black, harmlessly.
Updated 2026-11-01
Mechanism of action
In the gut, bismuth subsalicylate splits into bismuth and salicylate. Bismuth coats the mucosa, is directly toxic to bacteria (including Helicobacter pylori) and binds bacterial toxins. The salicylate, which is absorbed, reduces prostaglandin-driven secretion and inflammation. The net effect is less fluid and electrolyte flow into the bowel and fewer loose stools.
- In the gut it splits into bismuth and salicylate
- Bismuth coats the mucosa and harms bacteria such as H. pylori
- Salicylate lowers prostaglandin-driven secretion and inflammation
- Less fluid enters the bowel: fewer loose stools
Pharmacokinetics
- Absorption
- The salicylate is absorbed; very little bismuth is absorbed.
- Elimination
- Bismuth leaves mainly in the faeces as black bismuth sulfide; the salicylate is cleared like aspirin, by the liver and kidney.
Indications
- Bismuth quadruple therapy for Helicobacter pylori, with a PPI, metronidazole and tetracycline, where clarithromycin resistance is high. Helicobacter pylori gastritis →
- Acute diarrhoea, including travellers' diarrhoea, in adults and children from 12 years.
- Heartburn, indigestion and upset stomach.
Adverse effects
Common
- Black tongue and black stools (harmless, they fade a few days after stopping)
Contraindications
- Allergy to salicylates, including aspirin
- Children and adolescents with or recovering from chickenpox or influenza-like symptoms
- Active ulcer, a bleeding disorder, or bloody or black stools
Key interactions
- Aspirin and other salicylates
- More salicylate and a higher risk of toxicity (tinnitus).
- Anticoagulants such as warfarin
- More bleeding risk; the label asks for advice before use.
- Tetracyclines (doxycycline, minocycline, tetracycline)
- Lower antibiotic absorption; the antibiotic is taken well apart from it.
- Medicines for diabetes, gout or arthritis
- The salicylate can interfere with them; advice is sought before use.
What is monitored
- Tinnitus or hearing changes
- Fever, mucus or blood in the stool, or diarrhoea lasting more than two days, which need medical review
- Other salicylate sources the patient takes
Administration and safety
- Oral tablets, chewable tablets or suspension; the suspension is shaken before use
- The darkening of stool and tongue is expected and goes away a few days after stopping
- Fluids are kept up during diarrhoea to prevent dehydration
- In H. pylori regimens it is taken together with the other drugs for the whole course
Nursing care
- Warn the patient that black stools from bismuth are expected, and teach the signs that suggest real bleeding (dizziness, weakness, vomiting blood)
- Check for aspirin allergy and other salicylate products before giving it
- Do not give it to children or teenagers with chickenpox or flu-like illness
- Ask about ringing in the ears during treatment
Pregnancy and breastfeeding
It contains a salicylate; the patient leaflet asks pregnant or breastfeeding women to discuss its use with their doctor.
Test yourself
Think of the answer, then tap the question to see it.
Which drugs make up bismuth quadruple therapy for H. pylori?
A proton pump inhibitor, bismuth, metronidazole and tetracycline.
A patient on bismuth subsalicylate reports black stools but feels well and has a normal haemoglobin. What is the likely explanation?
Bismuth sulfide colouring the stool, a harmless effect of the drug.
Which symptom means bismuth subsalicylate should be stopped at once?
Ringing in the ears or hearing loss, a sign of salicylate toxicity.
Related drugs
Related conditions
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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 - BISMUTH SUBSALICYLATE tablet, film coated (DailyMed (U.S. National Library of Medicine), 2026); Bismuth Subsalicylate: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2016); Helicobacter pylori Infection - Gastroenterology - MSD Manual Professional Edition (MSD Manual Professional Edition, 2025).
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Representative model, for educational purposes only.