DMARD / Anti-inflammatory Pregnancy: Reproduction studies in rats and rabbits revealed no evidence of fetal harm, but sulfasalazine inhibits folic acid absorption/metabolism and neural tube defects have been reported in exposed pregnancies (role of the drug not established). Use during pregnancy only if clearly needed. Sulfasalazine and sulfapyridine are found in low levels in breast milk — avoid breastfeeding (reports of bloody stools/diarrhoea in breastfed infants) (eMC §4.6).

Sulfasalazine

Brand names: Salazopyrin EN

Sulfasalazine is used as a disease-modifying drug in rheumatoid and other inflammatory arthritis, and in inflammatory bowel disease.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Ulcerative colitis, moderate attack: 20 mL of 250 mg/5 mL oral suspension four times daily

Route: oral

Frequency: four times daily (night-time interval between doses not exceeding 8 hours)

Max: Severe attacks: up to 40 mL four times daily (with steroids, as part of an intensive management regime)

UK SPC §4.2 (Sulfasalazine 250 mg/5 mL oral suspension; 50 mg/mL). Ulcerative colitis — severe attacks: 20–40 mL four times daily with steroids as part of an intensive management regime (night-time interval ≤8 h; rapid passage of suspension may reduce effect). Moderate attacks: 20 mL four times daily, with or without steroids. Maintenance: on induction of remission, reduce the dose gradually to 40 mL per day, continued indefinitely (discontinuation, even years after an acute attack, is associated with a four-fold increase in relapse). Children: dose reduced in proportion to body weight — acute attack or relapse 0.8–1.2 mL/kg/day; maintenance 0.4–0.6 mL/kg/day (contraindicated under 2 years; verify paediatric dosing against a children's formulary). Crohn's disease (active): administer as in attacks of ulcerative colitis. US tablet labelling (cross-check): adults initial 3–4 g daily in evenly divided doses (intervals ≤8 h; may start 1–2 g daily to reduce GI intolerance), maintenance 2 g daily; children ≥6 years initial 40–60 mg/kg/day divided into 3–6 doses, maintenance 30 mg/kg/day divided into 4 doses.

Dose adjustments

Renal

No numeric dose adjustment stated; assess baseline renal function (including urinalysis) in all patients before starting, initiate in renal impairment only if benefits outweigh risk, monitor renal function periodically (especially early), and discontinue if renal function deteriorates (§4.4).

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

US labelling (FDA)

Reference — US labelling, may differ from UK

DOSAGE AND ADMINISTRATION The dosage of Sulfasalazine Tablets should be adjusted to each individual’s response and tolerance. Initial Therapy: Adults: 3 to 4 g daily in evenly divided doses with dosage intervals not exceeding eight hours. In some cases, it is advisable to initiate therapy with a smaller dosage, e.g., 1 to 2 g daily, to reduce possible gastrointestinal intolerance. If daily doses exceeding 4 g are required to achieve desired effects, the increased risk of toxicity should be kept in mind. Children, six years of age and older: 40 to 60 mg/kg body weight in each 24-hour period, divided into 3 to 6 doses. Maintenance Therapy: Adults: 2 g daily. Children, six years of age and …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2022-12-12. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Contraindications

Infants under the age of two years
Known hypersensitivity to sulfasalazine, its metabolites or any excipient, or to sulfonamides, salicylates or the sodium benzoate preservative
Porphyria
Intestinal or urinary obstruction (US labelling)

Side effects

Gastric distress, nausea (very common)
Headache, dizziness, taste disturbance (common)
Rash, pruritus, purpura (common)
Loss of appetite; raised temperature (common)
Leukopenia (common); apparently reversible oligospermia

Interactions

Folic acid — oral sulfasalazine inhibits its absorption and metabolism and may cause folic acid deficiency, potentially resulting in serious blood disorders (e.g. macrocytosis, pancytopenia) (§4.4/§4.6)

Clinical monograph

How it works

It is split in the colon into 5-aminosalicylic acid (acting locally in the gut) and sulfapyridine, the latter relevant to its systemic effects and toxicity.

Prescribing in practice

Blood dyscrasias and hepatotoxicity can occur, especially early — monitor FBC and liver function; rash and gastrointestinal upset are common.
It can harmlessly turn urine and soft contact lenses orange and cause a reversible reduction in sperm count.
Use caution in G6PD deficiency and sulphonamide allergy.

Monitoring

Monitor FBC and liver function regularly (more often at initiation); review response.

Counselling the patient

Report sore throat, fever, unexplained bruising, or yellowing of the skin/eyes.
It can turn urine and soft contact lenses orange (harmless).
It can take weeks to work.

Evidence & guidelines

A conventional DMARD in inflammatory arthritis and a treatment in inflammatory bowel disease, with FBC/LFT monitoring.

Reference: BSR/BHPR RA Guidelines; NICE NG100; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways