Olsalazine
5-ASA
Aminosalicylates (5-ASA)
Two mesalazine (5-ASA) molecules joined together; colonic bacteria split them. Used in ulcerative colitis when sulfasalazine is not tolerated.
Quick facts
- Group
- Aminosalicylates (5-ASA)
- Target
- Local anti-inflammatory action of mesalazine on the colonic mucosa
- Used for
- Ulcerative colitis
- Key effects
- Diarrhoea · Stomach upset · Headache
- Monitor
- Stool frequency and diarrhoea
- ATC
- A07EC03
No doses: the clinician sets them by the current guideline.
Mechanism of action
Olsalazine is two mesalazine molecules linked by an azo bond. It reaches the colon largely intact, where bacterial azoreduction releases two molecules of mesalazine. Mesalazine then reduces mucosal inflammation locally. Because there is no sulfapyridine carrier, the sulfonamide adverse effects of sulfasalazine are avoided.
- Olsalazine reaches the colon intact
- Bacteria split it into two mesalazine molecules
- Mesalazine reduces colonic inflammation
Indications
- Ulcerative colitis in adults who cannot tolerate sulfasalazine Ulcerative colitis →
Adverse effects
Common
- Diarrhoea
- Stomach upset, nausea, bloating, loss of appetite
- Headache, dizziness, poor sleep
- Joint or muscle pain
Contraindications
- Hypersensitivity to salicylates, mesalazine, sulfasalazine, balsalazide or olsalazine
- Varicella vaccine in the previous six weeks (Reye syndrome risk)
Key interactions
- Aspirin and other NSAIDs
- Added salicylate and kidney effects; checked before use
- Varicella vaccine
- Salicylate exposure after the vaccine raises the risk of Reye syndrome
What is monitored
- Stool frequency and diarrhoea
- Kidney and liver function
- Signs of intolerance reaction
Administration and safety
- Oral capsule, taken after meals or with food, with plenty of fluids.
- Urine may turn reddish-brown when it touches surfaces or toilet water; this is reported to the clinician.
- Sun protection is advised because of photosensitivity.
Pregnancy and breastfeeding
Human data are limited; use in pregnancy needs a clear benefit, keeping in mind that active colitis also carries risk.
Nursing care
- Ask about salicylate allergy, kidney and liver disease, and recent varicella vaccine.
- Track stool frequency: new watery diarrhoea is a known effect.
- Teach to report cramps with bloody diarrhoea and fever, jaundice, or rash.
Pharmacokinetics
- Metabolism
- Split by colonic bacteria (azoreduction)
Test yourself
Think of the answer, then tap the question to see it.
What is olsalazine made of?
Two mesalazine molecules joined by an azo bond.
Which vaccine is a reason to avoid it for some weeks?
Varicella vaccine, because of the risk of Reye syndrome.
Why can it be chosen over sulfasalazine?
It has no sulfapyridine, so sulfonamide adverse effects are avoided.
Connections
← Back to the class: Aminosalicylates (5-ASA)
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Olsalazine: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.