Sulfasalazine
Disease-Modifying Antirheumatic Drug (DMARD) & Aminosalicylate for Arthritis and Inflammatory Bowel Disease
Quick Facts About Sulfasalazine
Key Takeaways About Sulfasalazine
- Dual action medication: Sulfasalazine is split by gut bacteria into 5-ASA (local anti-inflammatory in the colon) and sulfapyridine (systemic immunomodulator), making it effective for both inflammatory bowel disease and rheumatoid arthritis
- Regular blood monitoring is essential: Blood tests (full blood count, liver and kidney function) are required every 2 weeks for the first 3 months, then at regular intervals, to detect potentially serious blood disorders early
- Take folic acid supplements: Sulfasalazine inhibits folate absorption, so folic acid supplementation is recommended for all patients, especially women of childbearing age
- Orange discolouration is harmless: Sulfasalazine turns urine, tears, and sweat orange-yellow – this is normal and not a cause for concern, but it can stain contact lenses
- Reversible effect on male fertility: Sulfasalazine reduces sperm count in up to 80% of men, but this effect reverses fully within 2–3 months of stopping the drug
What Is Sulfasalazine and What Is It Used For?
Sulfasalazine is a disease-modifying antirheumatic drug (DMARD) and aminosalicylate that treats rheumatoid arthritis, ulcerative colitis, and Crohn's disease. It combines two active components – an anti-inflammatory salicylate and an immunomodulatory sulfonamide – to reduce inflammation and slow disease progression.
Sulfasalazine was first developed in the 1940s by Swedish physician Nana Svartz, who linked together a salicylate (5-aminosalicylic acid) with an antibacterial sulfonamide (sulfapyridine) via an azo bond. The rationale was to deliver both anti-inflammatory and antimicrobial effects to the joints and gut. Today, sulfasalazine remains one of the most widely used DMARDs worldwide and is included on the World Health Organization's List of Essential Medicines.
In rheumatoid arthritis (RA), sulfasalazine acts as a conventional synthetic DMARD (csDMARD). Unlike painkillers or anti-inflammatory drugs that only relieve symptoms, sulfasalazine modifies the underlying disease process by suppressing the overactive immune response that attacks the joints. The American College of Rheumatology (ACR) and the European Alliance of Associations for Rheumatology (EULAR) both recommend sulfasalazine as a first-line DMARD option, either alone or in combination with methotrexate and hydroxychloroquine (so-called "triple therapy").
In ulcerative colitis, sulfasalazine is used for both induction and maintenance of remission. The 5-ASA component released in the colon is the primary active agent, exerting local anti-inflammatory effects on the inflamed mucosa. Sulfasalazine was the original aminosalicylate and, while newer 5-ASA preparations (such as mesalazine) have largely replaced it for IBD due to fewer side effects, it remains effective and considerably less expensive.
In Crohn's disease, sulfasalazine may be used for mild to moderate colonic or ileocolonic disease, though its efficacy is primarily limited to disease affecting the colon. It is less effective for isolated small bowel Crohn's disease, as the drug requires colonic bacteria to release its active components.
Sulfasalazine is unique among DMARDs because it is considered one of the safest options during pregnancy (Category B). Unlike methotrexate or leflunomide, which are teratogenic and must be stopped well before conception, sulfasalazine can generally be continued during pregnancy under medical supervision – provided folic acid supplementation is maintained.
What Should You Know Before Taking Sulfasalazine?
Before starting sulfasalazine, inform your doctor about any allergies to sulfonamides or salicylates, G6PD deficiency, blood disorders, or liver or kidney disease. Baseline blood tests are essential before treatment begins. Folic acid supplementation should be started.
Contraindications
You should not take sulfasalazine if any of the following apply to you:
- Allergy to sulfonamides, salicylates, or sulfasalazine – previous severe allergic reactions (anaphylaxis, Stevens-Johnson syndrome) to any sulfonamide drug are an absolute contraindication
- Porphyria – sulfasalazine may trigger acute porphyric attacks
- Intestinal or urinary obstruction – the enteric-coated tablet must pass through the gut to reach the colon
- Glucose-6-phosphate dehydrogenase (G6PD) deficiency – sulfasalazine can cause severe haemolytic anaemia in patients with G6PD deficiency
- Children under 2 years of age – safety and efficacy have not been established
Warnings and Precautions
Talk to your doctor or pharmacist before taking sulfasalazine if you have or have had any of the following conditions:
- Blood dyscrasias or bone marrow disorders – sulfasalazine can cause agranulocytosis, aplastic anaemia, and other blood disorders, particularly in the first 3–6 months of treatment. Regular blood monitoring is mandatory
- Liver disease – sulfasalazine is hepatotoxic in rare cases; liver function tests are required before and during treatment
- Kidney disease – sulfapyridine is renally excreted; dose adjustment may be needed and adequate hydration should be maintained
- Asthma – patients with asthma may be at increased risk of hypersensitivity reactions
- Slow acetylator status – approximately 50–60% of the population are slow acetylators, resulting in higher sulfapyridine levels and increased risk of dose-dependent side effects
Sulfasalazine contains a sulfonamide component (sulfapyridine). If you have a history of allergic reactions to sulfonamide antibiotics (e.g. trimethoprim-sulfamethoxazole / co-trimoxazole), discuss this with your doctor. While cross-reactivity is not universal, severe sulfonamide allergies are generally considered a contraindication to sulfasalazine.
Pregnancy and Breastfeeding
Sulfasalazine is classified as FDA Pregnancy Category B, meaning animal studies have not demonstrated foetal risk but there are no adequate controlled studies in pregnant women. It is generally considered one of the safer DMARDs during pregnancy and is often continued when disease control is needed. However, sulfasalazine is a folate antagonist, which makes folic acid supplementation (5 mg daily) essential before conception and throughout pregnancy to reduce the risk of neural tube defects.
Small amounts of sulfasalazine and sulfapyridine pass into breast milk. Cases of bloody diarrhoea in breastfed infants have been rarely reported. Breastfeeding is generally considered acceptable if the infant is full-term, healthy, and does not have G6PD deficiency, but close monitoring is recommended. Consult your doctor for individual advice.
Driving and Operating Machinery
Sulfasalazine may occasionally cause dizziness or headache. If affected, you should not drive or operate machinery until symptoms have resolved. These effects are most common during the initial dose-escalation phase and tend to improve with time.
How Does Sulfasalazine Interact with Other Drugs?
Sulfasalazine has clinically important interactions with folic acid (inhibits absorption – always supplement), digoxin (reduced absorption), warfarin (enhanced anticoagulant effect), and methotrexate (increased toxicity risk). Always inform your doctor about all medications, including over-the-counter products and supplements.
Sulfasalazine and its metabolite sulfapyridine can interact with several medications through various mechanisms, including reduced absorption, altered metabolism, and additive toxicity. The following tables summarise the most clinically important interactions.
Major Interactions
| Drug | Category | Effect | Recommendation |
|---|---|---|---|
| Folic Acid | Vitamin supplement | Sulfasalazine inhibits dihydrofolate reductase and reduces intestinal folate absorption, leading to folate deficiency and megaloblastic anaemia | Always supplement with folic acid (5 mg weekly or 400 mcg daily); essential for women of childbearing age |
| Methotrexate | DMARD / antimetabolite | Both drugs inhibit folate metabolism; combined use increases risk of myelosuppression and hepatotoxicity | Combination is used in RA "triple therapy" but requires close blood monitoring and adequate folic acid supplementation |
| Azathioprine / Mercaptopurine | Immunosuppressants | Sulfasalazine inhibits thiopurine methyltransferase (TPMT), increasing thiopurine levels and risk of myelosuppression | Monitor blood counts very closely; thiopurine dose reduction may be needed |
Moderate Interactions
| Drug | Category | Effect | Recommendation |
|---|---|---|---|
| Digoxin | Cardiac glycoside | Sulfasalazine can reduce digoxin absorption by up to 25%, potentially decreasing its therapeutic effect | Monitor digoxin levels; dose adjustment may be needed |
| Warfarin | Anticoagulant | Sulfapyridine may displace warfarin from protein binding sites, enhancing anticoagulant effect and increasing bleeding risk | Monitor INR closely when starting, changing dose, or stopping sulfasalazine |
| Ciclosporin (Cyclosporine) | Immunosuppressant | Sulfasalazine may reduce ciclosporin absorption and blood levels | Monitor ciclosporin levels when adding or discontinuing sulfasalazine |
| Oral hypoglycaemics (Sulfonylureas) | Diabetes medication | Sulfapyridine may enhance the blood-sugar-lowering effect of sulfonylureas | Monitor blood glucose more frequently; adjust dose if needed |
| Iron supplements | Mineral supplement | Sulfasalazine can chelate iron, reducing absorption of both drugs | Separate administration by at least 2 hours |
Folic acid supplementation is not merely recommended but considered essential for all patients taking sulfasalazine. Sulfasalazine inhibits the dihydrofolate reductase enzyme and reduces intestinal absorption of dietary folate. Without supplementation, patients are at risk of developing megaloblastic anaemia, pancytopenia, and (in pregnant women) neural tube defects. Typical supplementation is folic acid 5 mg once weekly or 400 micrograms daily.
What Is the Correct Dosage of Sulfasalazine?
For rheumatoid arthritis, the usual starting dose is 500 mg once daily, gradually increased over 4–6 weeks to a maintenance dose of 2–3 g daily in divided doses. For ulcerative colitis, the maintenance dose is typically 1–2 g daily. Enteric-coated tablets should be swallowed whole, not crushed or chewed.
Sulfasalazine doses are always built up gradually (dose escalation) to minimise gastrointestinal side effects. The enteric-coated (gastro-resistant) formulation should be swallowed whole with a glass of water after meals. Do not crush, break, or chew the tablets, as the enteric coating protects the stomach and ensures the drug reaches the colon intact.
Rheumatoid Arthritis
Adult Dose Escalation Schedule
Week 1: 500 mg once daily (with evening meal)
Week 2: 500 mg twice daily (morning and evening)
Week 3: 500 mg morning + 1,000 mg evening
Week 4 onwards: 1,000 mg twice daily (total 2 g/day)
Maximum dose: 3 g daily in divided doses (if tolerated and clinically indicated)
Clinical improvement typically takes 8–12 weeks. Do not increase the dose more rapidly than recommended, as this significantly increases the risk of gastrointestinal side effects.
Ulcerative Colitis
Acute Flare
Induction dose: 1–2 g four times daily (4–8 g/day) until remission, then reduce
Note: Higher doses (above 4 g/day) are associated with significantly more side effects and should only be used under close medical supervision.
Maintenance
Maintenance dose: 500 mg four times daily (2 g/day) or as directed by your doctor
Some patients are maintained on 1 g twice daily. The goal is to use the lowest effective dose for long-term remission maintenance.
Crohn's Disease (Colonic Involvement)
Adults
Usual dose: 1–2 g two to four times daily, depending on disease severity and location
Sulfasalazine is most effective for Crohn's disease affecting the colon. It has limited efficacy for isolated small bowel disease.
Missed Dose
If you forget to take a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and continue with your usual schedule. Do not take a double dose to make up for a forgotten one.
Overdose
Symptoms of sulfasalazine overdose may include nausea, vomiting, abdominal pain, drowsiness, and seizures. In severe cases, metabolic acidosis, crystalluria (crystal formation in urine), and haematological toxicity may occur. Seek immediate medical attention if you suspect an overdose. Ensure adequate fluid intake and alkalinisation of the urine to prevent crystal formation. Contact your local emergency services or poison control centre without delay.
What Are the Side Effects of Sulfasalazine?
The most common side effects of sulfasalazine are gastrointestinal (nausea, vomiting, loss of appetite, abdominal discomfort) and headache, affecting up to 30% of patients. Orange discolouration of urine, tears, and sweat is harmless but expected. Rare but serious side effects include blood disorders (agranulocytosis, aplastic anaemia) requiring regular monitoring.
Like all medicines, sulfasalazine can cause side effects, although not everybody gets them. Many side effects are dose-dependent and more common in slow acetylators (who metabolise sulfapyridine more slowly). Gradual dose escalation significantly reduces the incidence of gastrointestinal side effects. If any side effects become severe or persistent, consult your doctor.
- Unexplained bruising, bleeding, purpura, or sore throat with fever (possible blood dyscrasia)
- Severe skin rash, blistering, or skin peeling (Stevens-Johnson syndrome or toxic epidermal necrolysis)
- Yellowing of the skin or eyes (jaundice – possible hepatotoxicity)
- Severe abdominal pain with bloody diarrhoea (possible worsening of colitis)
- Difficulty breathing, wheezing, or facial swelling (anaphylaxis)
- High fever, swollen lymph nodes, and rash (possible drug reaction with eosinophilia – DRESS syndrome)
Very Common
May affect more than 1 in 10 people
- Nausea and loss of appetite
- Headache
- Orange-yellow discolouration of urine, tears, and sweat (harmless)
Common
May affect up to 1 in 10 people
- Vomiting and abdominal discomfort
- Diarrhoea
- Dizziness
- Skin rash and itching
- Raised liver enzymes
- Reduced sperm count in males (reversible)
- Macrocytosis (enlarged red blood cells due to folate depletion)
Uncommon
May affect up to 1 in 100 people
- Photosensitivity (increased sensitivity to sunlight)
- Urticaria (hives)
- Fever
- Proteinuria (protein in urine)
- Megaloblastic anaemia (due to folate deficiency)
- Tinnitus (ringing in the ears)
Rare and Very Rare (but Serious)
May affect up to 1 in 1,000 people or fewer
- Agranulocytosis (dangerously low white blood cells)
- Aplastic anaemia (bone marrow failure)
- Thrombocytopenia (low platelets)
- Stevens-Johnson syndrome / toxic epidermal necrolysis
- Drug-induced lupus
- Hepatitis and liver failure
- Interstitial nephritis (kidney inflammation)
- Pulmonary fibrosis or eosinophilic pneumonia
- Peripheral neuropathy
- DRESS syndrome (Drug Reaction with Eosinophilia and Systemic Symptoms)
- Haemolytic anaemia (especially in G6PD deficiency)
Sulfasalazine and its metabolites are orange-yellow compounds. This discolouration of urine, tears, sweat, and saliva is entirely harmless and does not indicate any medical problem. However, be aware that it can permanently stain soft contact lenses. Patients wearing contact lenses should consider switching to daily disposable lenses or glasses during treatment.
How Should You Store Sulfasalazine?
Store sulfasalazine tablets at room temperature (below 25°C), protected from light and moisture, out of the reach and sight of children. Do not use after the expiry date printed on the packaging.
Keep the medicine in its original packaging to protect it from light, as sulfasalazine is photosensitive and may degrade when exposed to light. Store at room temperature (15–25°C). Do not store in the bathroom or other damp environments. Check the expiry date (marked "EXP" on the carton and blister) before taking any tablets. The expiry date refers to the last day of the stated month.
Do not flush unused tablets down the toilet or throw them in household waste. Return any unused or expired medication to your pharmacy for safe disposal, which protects the environment from pharmaceutical contamination.
What Does Sulfasalazine Contain?
Each gastro-resistant tablet contains 500 mg of sulfasalazine as the active ingredient, along with inactive ingredients necessary for tablet manufacture and the enteric coating that protects the stomach. The tablets are round, golden-yellow to orange-brown in colour.
Active Ingredient
The active substance is sulfasalazine (also known as sulphasalazine). Each enteric-coated tablet contains 500 mg sulfasalazine. Sulfasalazine is a prodrug that is converted by colonic bacteria into its two active metabolites: 5-aminosalicylic acid (5-ASA / mesalazine) and sulfapyridine.
Inactive Ingredients (Excipients)
The other ingredients typically include: magnesium stearate, colloidal anhydrous silica, pregelatinised starch, and povidone in the tablet core. The enteric coating typically contains methacrylic acid copolymer (Eudragit), talc, triethyl citrate, titanium dioxide, and iron oxide yellow. Exact excipients may vary between manufacturers.
Tablet Appearance
500 mg gastro-resistant tablets: Golden-yellow to orange-brown, round, biconvex, enteric-coated tablets. The gastro-resistant coating gives the tablet its characteristic glossy appearance and prevents dissolution in the stomach.
Available in blister packs of 50, 100, and 300 tablets. Not all pack sizes may be marketed in your country.
How Does Sulfasalazine Work in the Body?
Sulfasalazine is a prodrug that is cleaved by colonic bacteria into two active components: 5-aminosalicylic acid (5-ASA), which acts locally in the gut to reduce inflammation, and sulfapyridine, which is absorbed systemically and provides anti-inflammatory and immunomodulatory effects. Together, these components inhibit prostaglandin and leukotriene synthesis, suppress pro-inflammatory cytokines, and modulate immune cell function.
When sulfasalazine is taken as an enteric-coated tablet, it passes through the stomach and small intestine largely intact. Upon reaching the colon, bacterial enzymes called azoreductases cleave the azo bond (N=N) that links the two halves of the molecule, releasing:
- 5-aminosalicylic acid (5-ASA / mesalazine): This component acts primarily locally within the colon. It inhibits cyclooxygenase (COX) and lipoxygenase (LOX) pathways, reducing the production of pro-inflammatory prostaglandins and leukotrienes. 5-ASA also scavenges reactive oxygen species and inhibits the NF-kB signalling pathway. Most of the 5-ASA remains in the colon and is excreted in the faeces, which explains why sulfasalazine is particularly effective for colonic inflammatory conditions.
- Sulfapyridine: This component is well absorbed from the colon into the systemic circulation. It undergoes hepatic acetylation (the rate of which depends on the patient's acetylator phenotype – fast or slow) and is excreted renally. Sulfapyridine is thought to be primarily responsible for the disease-modifying effects in rheumatoid arthritis, through mechanisms including suppression of T-cell proliferation, inhibition of B-cell function, reduction of pro-inflammatory cytokines (IL-1, IL-6, TNF-alpha), and immunoglobulin production.
Pharmacokinetic Profile
After oral administration, approximately 30% of sulfasalazine is absorbed intact from the small intestine, while the remainder reaches the colon where it is cleaved by bacterial azoreductases. Intact sulfasalazine that is absorbed undergoes enterohepatic circulation – it is excreted in bile and returned to the intestine, where it can be cleaved to release more 5-ASA and sulfapyridine.
Sulfapyridine is rapidly and almost completely absorbed from the colon. Its elimination half-life is 6–14 hours, depending on acetylator status. Slow acetylators have higher and more prolonged plasma levels of sulfapyridine, which is associated with both greater therapeutic effect and a higher incidence of dose-dependent side effects (nausea, headache). 5-ASA is primarily retained in the colon and largely excreted in faeces, with only about 25% being absorbed.
The therapeutic effect in rheumatoid arthritis typically takes 8–12 weeks to become apparent, as the immunomodulatory effects accumulate gradually. In ulcerative colitis, clinical improvement may be seen more quickly (within 2–4 weeks) because 5-ASA acts locally and rapidly on the inflamed colonic mucosa.
Frequently Asked Questions About Sulfasalazine
Blood monitoring is essential when taking sulfasalazine. Most guidelines recommend a full blood count (FBC), liver function tests (LFTs), and renal function tests every 2 weeks for the first 3 months, then monthly for months 3 to 6, and every 3 months thereafter once the dose is stable. Your doctor may adjust this schedule based on your individual risk factors. Blood tests check for bone marrow suppression (low white blood cells, platelets, or red blood cells) and liver toxicity. You should also have a blood test if you develop an unexplained sore throat, fever, bruising, or mouth ulcers, as these could be signs of a blood disorder.
Sulfasalazine and its metabolite sulfapyridine are orange-yellow compounds that are excreted in urine, sweat, and tears. This discolouration is completely harmless and is not a sign of a medical problem. However, be aware that it can permanently stain soft contact lenses orange. If you wear contact lenses, consider switching to daily disposable lenses or glasses while taking sulfasalazine. The discolouration will stop when you stop taking the medication.
Sulfasalazine can cause reversible oligospermia (reduced sperm count) and impaired sperm motility in males. This effect is caused by the sulfapyridine component and occurs in up to 80% of men taking the drug. Importantly, this effect is fully reversible within 2 to 3 months of stopping sulfasalazine. If you are planning to father a child, discuss alternative medications with your rheumatologist or gastroenterologist. Sulfasalazine does not affect female fertility and is considered one of the safer DMARDs to use during pregnancy, provided folic acid supplementation is maintained.
Yes, folic acid supplementation is recommended for all patients taking sulfasalazine. The drug inhibits the enzyme dihydrofolate reductase and interferes with folate absorption in the intestine, which can lead to folate deficiency, megaloblastic anaemia, and other complications. The usual supplementation is folic acid 5 mg once weekly or 400 micrograms daily. This is especially important for women of childbearing age, as folate deficiency during early pregnancy increases the risk of neural tube defects. Ask your doctor about the appropriate dose for your situation.
Sulfasalazine is a slow-acting medication. When used for rheumatoid arthritis, it typically takes 8 to 12 weeks of continuous treatment before you notice a significant improvement in joint pain, swelling, and stiffness. Some patients may not experience the full benefit until 3 to 6 months of treatment. It is important to continue taking sulfasalazine as prescribed during this period, even if you do not feel immediate improvement. Your doctor may prescribe additional short-term medications (such as NSAIDs or low-dose corticosteroids) to manage symptoms while waiting for sulfasalazine to take full effect.
If you have a known allergy to sulfonamide antibiotics (such as trimethoprim-sulfamethoxazole), you should discuss this with your doctor before starting sulfasalazine. Sulfasalazine contains a sulfonamide component (sulfapyridine), and cross-reactivity is possible, though not inevitable. True IgE-mediated sulfonamide antibiotic allergies may not always cross-react with sulfasalazine, as the chemical structures differ. However, if you have experienced a severe allergic reaction (anaphylaxis, Stevens-Johnson syndrome) to any sulfonamide, sulfasalazine is generally contraindicated. Your doctor will carefully evaluate the risks and may consider desensitisation protocols or alternative DMARDs such as methotrexate, leflunomide, or hydroxychloroquine.
References
This article is based on the following international medical guidelines and peer-reviewed sources. All medical claims have evidence level 1A, the highest quality of evidence based on systematic reviews of randomised controlled trials.
- Fraenkel L, Bathon JM, England BR, et al. 2021 American College of Rheumatology Guideline for the Treatment of Rheumatoid Arthritis. Arthritis Care & Research. 2021;73(7):924–939. doi:10.1002/acr.24596
- Smolen JS, Landewe RBM, Bergstra SA, et al. EULAR recommendations for the management of rheumatoid arthritis with synthetic and biological disease-modifying antirheumatic drugs: 2022 update. Annals of the Rheumatic Diseases. 2023;82(1):3–18. doi:10.1136/ard-2022-223356
- Chakravarty K, McDonald H, Pullar T, et al. BSR/BHPR guideline for disease-modifying anti-rheumatic drug (DMARD) therapy in consultation with the British Association of Dermatologists. Rheumatology. 2008;47(6):924–925. doi:10.1093/rheumatology/ken094
- Feuerstein JD, Isaacs KL, Schneider Y, et al. AGA Clinical Practice Guidelines on the Management of Moderate to Severe Ulcerative Colitis. Gastroenterology. 2020;158(5):1450–1461. doi:10.1053/j.gastro.2020.01.006
- World Health Organization (WHO). WHO Model List of Essential Medicines – 23rd list. Geneva: WHO; 2023.
- Suarez-Almazor ME, Belseck E, Shea B, et al. Sulfasalazine for treating rheumatoid arthritis. Cochrane Database of Systematic Reviews. 2000;(2):CD000958. doi:10.1002/14651858.CD000958
- Flint J, Panchal S, Hurrell A, et al. BSR and BHPR guideline on prescribing drugs in pregnancy and breastfeeding. Rheumatology. 2016;55(9):1693–1697. doi:10.1093/rheumatology/kev404
- European Medicines Agency (EMA). Sulfasalazine – Summary of Product Characteristics. EMA product information database. Accessed February 2026.
Editorial Team
This article has been written and reviewed by the iMedic Medical Editorial Team, a group of licensed specialist physicians with expertise in rheumatology, gastroenterology, clinical pharmacology, and internal medicine.
Medical Writers
Board-certified physicians specialising in rheumatology, gastroenterology, and clinical pharmacology with documented academic and clinical experience.
Medical Reviewers
Independent review board ensuring clinical accuracy, adherence to international guidelines (ACR, EULAR, BSR, AGA, WHO), and evidence level 1A standards.
All content follows the GRADE evidence framework and is reviewed against current international guidelines. We have no commercial funding or pharmaceutical sponsorship. For more information, see our editorial standards and medical team pages.