[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Aminosalicylates (5-ASA)](https://durgical.com/en/pharmacology/classes/aminosalicylates/) › Sulfasalazine

[Pharmacology](https://durgical.com/en/pharmacology/) · [Aminosalicylates (5-ASA)](https://durgical.com/en/pharmacology/classes/aminosalicylates/)

# Sulfasalazine

A pro-drug that colonic bacteria split into 5-ASA, which calms the colon, and sulfapyridine. Used in ulcerative colitis and rheumatoid arthritis.

Updated 2026-11-01

- Class: [Aminosalicylates (5-ASA)](https://durgical.com/en/pharmacology/classes/aminosalicylates/)
- Target: Colonic mucosa (5-ASA) and immune cells (anti-inflammatory and immunomodulatory effects)
- ATC code: A07EC01
- WHO Model List of Essential Medicines

Also called: Salazosulfapyridine

## Mechanism of action

Sulfasalazine is 5-aminosalicylic acid joined to sulfapyridine by an azo bond, which keeps it from being absorbed in the small bowel. In the colon, bacterial azoreductases break the bond. 5-ASA acts topically on the inflamed mucosa and is the main active part in ulcerative colitis. Sulfapyridine is absorbed, is acetylated in the liver and causes most adverse effects; its immunomodulatory action may help in rheumatoid arthritis.

- Azo bond keeps the drug intact through the small bowel
- Colonic bacteria split it into 5-ASA and sulfapyridine
- 5-ASA calms the colonic mucosa locally
- Absorbed sulfapyridine causes most adverse effects

## Pharmacokinetics

**Absorption**
Little of the parent drug is absorbed; sulfapyridine is well absorbed from the colon, 5-ASA much less

**Distribution**
The parent drug is highly bound to albumin

**Metabolism**
Bacterial azo reduction in the colon; sulfapyridine is acetylated in the liver at a rate set by acetylator status

**Elimination**
Sulfapyridine and its metabolites in urine; most 5-ASA in stool

## Indications

- Mild to moderate ulcerative colitis, and as an add-on in severe disease [Ulcerative colitis →](https://durgical.com/en/conditions/ulcerative-colitis/)
- Maintenance of remission in ulcerative colitis [Ulcerative colitis →](https://durgical.com/en/conditions/ulcerative-colitis/)
- Crohn's disease [Crohn disease →](https://durgical.com/en/conditions/crohn-disease/)
- Rheumatoid arthritis not controlled by NSAIDs [Rheumatoid arthritis →](https://durgical.com/en/conditions/rheumatoid-arthritis/)
- Polyarticular juvenile idiopathic arthritis

## Adverse effects

### Common

- Nausea, loss of appetite and stomach upset
- Headache
- Rash and itching
- Orange-yellow urine or skin; can stain soft contact lenses
- Reversible low sperm count and infertility in men

### Serious (rare, important)

- Agranulocytosis, aplastic anaemia and other blood dyscrasias
- Haemolytic anaemia in G6PD deficiency
- Severe skin reactions (SJS/TEN, DRESS, exfoliative dermatitis)
- Hepatitis, nephritis, pneumonitis and fibrosing alveolitis
- Serious infections, including sepsis

## Contraindications

- Hypersensitivity to sulfasalazine, sulfonamides or salicylates
- Intestinal or urinary obstruction
- Porphyria

## Key interactions

**Folic acid**
Sulfasalazine lowers folate absorption; folate supplements are often added

**Digoxin**
Lower digoxin absorption

## What is monitored

- Complete blood count with differential and liver tests before starting, often in the first months, then less often
- Urinalysis and kidney function periodically
- Sore throat, fever, pallor, purpura or jaundice (possible blood or liver toxicity)
- Rash or fever early in treatment

## Administration and safety

- Delayed-release tablets are swallowed whole and taken in divided doses, preferably after meals.
- Good fluid intake prevents crystals and stones in the urine.

## Nursing care

- Ask about sulfonamide or salicylate allergy and G6PD deficiency before the first dose.
- Check that baseline blood counts and liver tests are done.
- Teach that orange urine is harmless, and that sore throat, fever, bruising or yellow skin are reported at once.
- Encourage plenty of fluids.
- Tell men that low sperm count can occur and usually reverses after stopping.

## Pregnancy and breastfeeding

There is no clear evidence of harm in pregnancy; because it lowers folate, extra folic acid is given before conception and in early pregnancy. Breastfeeding may be possible if the baby is healthy.

## Memory aid

SulfaSALAZINE = Sulfa + SALicylate: sulfapyridine brings the side effects, 5-ASA brings the benefit.

## Test yourself

Think of the answer, then tap the question to see it.

## What are the two products of sulfasalazine in the colon, and which one causes most adverse effects?

5-ASA and sulfapyridine; sulfapyridine causes most adverse effects.

## Why do slow acetylators have more sulfasalazine adverse effects?

They clear sulfapyridine more slowly, so its levels rise.

## Which vitamin is lowered by sulfasalazine and often supplemented?

Folate (folic acid).

## Which blood problem can sulfasalazine cause in G6PD deficiency?

Haemolytic anaemia.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/pharmacology/sulfasalazine/)

## Related drugs

- [Mesalazine](https://durgical.com/en/pharmacology/mesalazine/)
- [Methotrexate](https://durgical.com/en/pharmacology/methotrexate/)
- [Hydroxychloroquine](https://durgical.com/en/pharmacology/hydroxychloroquine/)

## Related conditions

- [Ulcerative colitis](https://durgical.com/en/conditions/ulcerative-colitis/)
- [Crohn disease](https://durgical.com/en/conditions/crohn-disease/)
- [Rheumatoid arthritis](https://durgical.com/en/conditions/rheumatoid-arthritis/)

[← Back to the class: Aminosalicylates (5-ASA)](https://durgical.com/en/pharmacology/classes/aminosalicylates/)

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 - SULFASALAZINE tablet, delayed release](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=257cee60-b68f-4c2b-b57d-8e4d73d17e09) (DailyMed (U.S. National Library of Medicine), 2026); [Sulfasalazine: a medicine for ulcerative colitis, Crohn's disease and rheumatoid arthritis - NHS](https://www.nhs.uk/medicines/sulfasalazine/) (NHS (National Health Service, UK), 2025); [Sulfasalazine: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a682204.html) (MedlinePlus (U.S. National Library of Medicine), 2024); Farmacología básica y clínica (Katzung), 16.ª ed., cap. 62 (McGraw Hill, 2025).

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Representative model, for educational purposes only.

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