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)
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 →
Maintenance of remission in ulcerative colitis Ulcerative colitis →
Crohn's disease Crohn disease →
Rheumatoid arthritis not controlled by NSAIDs 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

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.

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.

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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 - SULFASALAZINE tablet, delayed release (DailyMed (U.S. National Library of Medicine), 2026); Sulfasalazine: a medicine for ulcerative colitis, Crohn's disease and rheumatoid arthritis - NHS (NHS (National Health Service, UK), 2025); Sulfasalazine: MedlinePlus Drug Information (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.