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Azulfidine (Sulfasalazine)

Last updated on November 28, 2023


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What is the other name for Azulfidine?

Azulfidine may be marketed under different names in various countries. Some of them are the following: Aculfin, Azulfidina, Azulfin, Colo-Pleon, Flogostop, Pleon RA, Pyralin, SAS, Salazopirina, Salazoprin, Salazopryn, Salazopyrin, Salazopyrina, Salazopyrine, Salisulf Gastroprotetto, Salopyrine, Sulazine, Sulfazine, Ulcol.

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(British Approved Name, US Adopted Name, rINN)

What Is Azulfidine (Sulfasalazine)?


Azulfidine, or Sulfasalazine, is a medication primarily used to treat inflammatory bowel diseases such as ulcerative colitis and Crohn’s disease. It belongs to a class of disease-modifying antirheumatic drugs (DMARDs). The active component, sulfasalazine, combines sulfapyridine and 5-aminosalicylic acid (5-ASA).

Azulfidine reduces inflammation in the digestive tract, helping alleviate symptoms like abdominal pain, diarrhea, and rectal bleeding. It is often prescribed to manage chronic conditions and may take some time to show its full therapeutic effects. As with any medication, individuals need to discuss potential side effects and interactions with their healthcare provider.


About 15% of an oral dose of sulfasalazine is absorbed from the small intestine, although some of this is subsequently returned to the intestine in bile via enterohepatic circulation. Most of the dose reaches the colon, where the azo bond is cleaved by the action of the intestinal flora, producing sulfapyridine and 5-aminosalicylic acid (mesalazine). Results in patients who have undergone colectomy suggest that between 60 and 90% of the total dose is metabolized in this way. Still, the degree of metabolism depends on the activity of the intestinal flora. The speed of intestinal transit colonic metabolism is reduced in patients with diarrhea (for example, in active inflammatory bowel disease).

The small amount of intact sulfasalazine absorbed is extensively protein-bound and subsequently excreted unchanged in urine. It crosses the placenta and is found in breast milk.

After cleavage of the sulfasalazine molecule, about 60 to 80% of available sulfapyridine is absorbed and undergoes extensive metabolism by acetylation, hydroxylation, and glucuronidation. Peak steady-state concentrations of sulfapyridine are higher in slow acetylators than fast acetylators after similar doses, and the former is 2 to 3 times more likely to have adverse effects. Some 60% of the original dose of sulfasalazine is excreted in urine as sulfapyridine and its metabolites. As with sulfasalazine, absorbed sulfapyridine crosses the placenta and is found in breast milk.

The 5-aminosalicylic acid (5-ASA) moiety is much less well absorbed. About one-third of liberated 5-ASA is absorbed; almost all of this is acetylated and excreted in urine. For further details of the pharmacokinetics of 5-aminosalicylic acid.

Uses and Administration

Sulfasalazine is a sulfonamide compound, sulfapyridine, with 5-aminosalicylic acid (mesalazine). Its activity generally lies in the 5-aminosalicylic acid moiety released in the colon by bacterial metabolism. However, intact sulfasalazine has some anti-inflammatory properties in its own right.

In inflammatory bowel disease, it is used alone or as an adjunct to corticosteroids in treating active ulcerative colitis and is effective in maintaining remission. Sulfasalazine may also be effective in treating active Crohn’s disease, particularly of the colon, but it does not appear to be of value in maintaining remissions. Sulfasalazine is also used as a disease-modifying drug in the treatment of severe or progressive rheumatoid arthritis (below).

In inflammatory bowel disease, the usual initial adult dose of sulfasalazine is 1 to 2 g orally four times daily in the UK. However, doses over 4 g daily are associated with an increased risk of toxicity, and in the USA, therefore, the usual dose is 1 g given 3 or 4 times daily, and an initial dose of 500 mg every 6 to 12 hours may be recommended to lessen gastrointestinal adverse effects. Enteric-coated tablets are also claimed to reduce the incidence of adverse gastrointestinal effects. The overnight interval between doses should be at most 8 hours. On remission, the dose in patients with ulcerative colitis is gradually reduced to 2 g daily and generally continued indefinitely. For children two years or older, doses should be proportional to body weight; initially, 40 to 60 mg/kg may be given daily in divided doses reduced to 20 to 30 mg/kg daily to maintain remission.

Sulfasalazine is also given rectally, as suppositories, initially at a dose of 1 g at night and in the morning. After three weeks, the dosage is gradually reduced according to response. Rectal sulfasalazine can be given as 0.5 to 1 g night and morning as an adjunct to treatment by mouth. Sulfasalazine may also be given by enema in a dose of 3 g at bedtime. The BNFC suggests the following daily dosage may be given in divided doses to children as suppositories according to age: 5 to 8 years old: 1 g 8 to 12 years old: 1.5 g 12 to 18 years old: 2 g. Enemas, to be retained for at least 1 hour, may be given at night in doses of 1 to 1.5 g for children aged 2 to 7 years, 1.5 to 2.25 g for children aged 7 to 12 years, and 3 g for children 12 to 18 years.

In adult rheumatoid arthritis, treatment is usually started with an oral dose of 500 mg daily, as enteric-coated tablets, for the first week; the dosage is then increased by 500 mg daily each week to a maximum of 3 g daily given in 2 to 4 divided doses according to tolerance and response. In the USA, sulfasalazine can also be used for polyarticular juvenile rheumatoid arthritis in children aged six years and older who have not responded adequately to salicylates or other NSAIDs. 30 to 50 mg/kg daily is given in two divided doses, to a maximum dose of 2 g daily. An enteric-coated tablet is used to reduce adverse gastrointestinal effects. The initial dose should be a quarter to a third of the planned maintenance. It is then increased weekly to reach the maintenance dose after one month.

Although sulfasalazine is not licensed for juvenile rheumatoid arthritis in the UK, the BNFC suggests that children aged 2 to 18 are given an initial oral dose of 5 mg/kg twice daily for one week. The dose is then increased to 10 mg/kg twice daily for one week, then 20 mg/kg twice daily for one week, and maintained on a dose of 20 to 25 mg/kg twice daily. For children aged 2 to 12 years, the maximum dose suggested is 2 g daily, and for children aged 12 to 18 years, 3 g daily.


In a double-blind placebo-controlled study involving 50 patients with moderate to severe plaque-type psoriasis, sulfasalazine 3 to 4g per day produced more significant clinical improvement than placebo after four weeks of treatment, with a further improvement at eight weeks. See also Psoriatic Arthritis.

Pyoderma Gangrenosum

Sulfasalazine is licensed in some countries for the treatment of pyoderma gangrenosum, a condition that may be associated with inflammatory bowel disease, although published evidence of benefit is scanty.

Rheumatoid Arthritis

Sulfasalazine is considered to be a useful disease-modifying antirheumatic drug (DMARD) in the treatment of rheumatoid arthritis. Studies have found a beneficial clinical effect of sulfasalazine, compared with placebo, on tender and swollen joints, pain, and erythrocyte sedimentation rate. Meta-analyses of generally short-term comparative studies suggest that sulfasalazine is roughly comparable in efficacy to methotrexate, intramuscular gold (sodium aurothiomalate), and penicillamine. Other reviews have also suggested that it may have similar efficacy to hydroxychloroquine and leflunomide.

Although regional differences exist in prescribing DMARDs, sulfasalazine has been widely used for initial therapy, especially for less severe diseases. In an open study of 200 patients with rheumatoid arthritis who were randomly allocated to treatment with sulfasalazine or auranofin, 31 % of the sulfasalazine recipients were still taking the drug after five years compared with 15% of auranofin recipients. An improvement over baseline was still significant at five years for those patients receiving sulfasalazine but not in those treated with auranofin.

Although one study failed to find convincing evidence that using sulfasalazine with methotrexate was more effective than either drug alone, other studies have shown that combination treatment with sulfasalazine plus methotrexate, and hydroxychloroquine was more effective than methotrexate alone or with sulfasalazine or hydroxychloroquine or the combination of sulfasalazine with hydroxychloroquine. A review of sulfasalazine use in the management of rheumatoid arthritis concluded that combination therapy may be of benefit in patients with early or advanced rheumatoid arthritis but that there is still a need for studies to determine the efficacy and tolerability of various combinations.

Juvenile Idiopathic Arthritis

Juvenile idiopathic arthritis is generally managed similarly to rheumatoid arthritis, but there is limited experience with the use of some antirheumatic drugs in children. Sulfasalazine has produced significant improvement in studies of patients with juvenile chronic arthritis. A literature review found that it was consistently reported to be of benefit. Adverse effects were reported to be similar to those in adults, except for a serum-sickness-like reaction, primarily seen in systemic onset patients. They may be unique to juvenile rheumatoid arthritis.

Spondyloarthropathies. Ankylosing Spondylitis

Sulfasalazine is effective in the treatment of active ankylosing spondylitis. Still, evidence shows it is more helpful in treating active disease and peripheral articular manifestations than managing chronic, long-standing disease. The active moiety appears to be sulfapyridine rather than mesalazine. Sulfasalazine was no better than a placebo for the treatment of inflammatory back pain due to undifferentiated spondyloarthritis and early ankylosing spondylitis. Still, it was more effective than placebo in a subgroup of patients with no peripheral arthritis.

Adverse Effects and Precautions

Since sulfasalazine is metabolized to sulfapyridine and 5-aminosalicylic acid (mesalazine), its adverse effects and precautions are similar to those of sulfonamides (see Sulfamethoxazole) and mesalazine. Many adverse effects have been attributed to the sulfapyridine moiety and appear to be more common if serum-sulfapyridine concentrations are greater than 50 micrograms/ml if the daily dose of sulfasalazine is 4 g or more or in slow acetylators of sulfapyridine.

The most commonly reported adverse effects include nausea and vomiting, abdominal discomfort, headache, fever, and skin rash. Adverse effects can be divided into two groups:

  • Dose-related effects are dependent on acetylator phenotype and largely predictable. This group includes nausea, vomiting, headache, hemolytic anemia, and methemoglobinemia.
  • Hypersensitivity reactions are unpredictable and usually occur at the start of treatment. This group includes skin rash, aplastic anemia, hepatic and pulmonary dysfunction, and auto-immune hemolysis.

Oligospermia, reversible on withdrawal of sulfasalazine, has also been reported. Sulfasalazine treatment may result in yellow-orange discoloration of skin, urine, and other body fluids. Some soft contact lenses may be stained.

Sulfasalazine should not be given to patients with a history of sensitivity to sulfonamides or salicylates. Use in children under two years of age is contra-indicated because of the risk of kernicterus. Blood counts should be performed at the start of therapy and at least once a month for a minimum of the first three months of treatment. If a blood dyscrasia is suspected, treatment should be stopped immediately, and a blood count should be performed. Patients or their carers should be told how to recognize signs of blood toxicity and should be advised to seek immediate medical attention if symptoms such as fever, sore throat, mouth ulcers, bruising, or bleeding develop. Care is advisable in patients with G6PD deficiency because of the risk of hemolytic anemia.

Sulfasalazine should be used with caution in hepatic or renal impairment. Liver function tests should be carried out monthly for the first three months of treatment. Periodic monitoring of kidney function has also been recommended.

The adverse effects associated with the use of sulfasalazine in patients with inflammatory bowel disease or rheumatoid arthritis have been reviewed. The type and incidence of adverse effects are similar in both groups of patients. Although most reactions are minor, and patients may continue therapy at the same or reduced dosage, some patients stop treatment because of adverse effects. In these cases, a hyposensitization regimen may be considered. Hyposensitization should not be attempted in patients with a history of severe adverse effects such as agranulocytosis, toxic epidermal necrolysis, erythema multiforme, frank hemolysis, or a severe hypersensitivity reaction.

An alternative to hyposensitization in patients with inflammatory bowel disease who cannot tolerate sulfasalazine is to try a drug that supplies the active 5-aminosalicylic acid component without sulfapyridine, as the latter is thought to be responsible for many of the adverse effects. Examples include balsalazide, mesalazine, and olsalazine; however, some patients still experience hypersensitivity, see under Mesalazine.


Small amounts of sulfasalazine and its sulfapyridine metabolites are excreted in breast milk. The sulfasalazine and total sulfapyridine concentrations may be up to 30% and 50% of maternal serum concentrations, respectively. Bloody diarrhea in a breastfed infant whose mother was taking sulfasalazine 3 g daily has been reported. The mother was a slow acetylator with a relatively high blood concentration of sulfapyridine, which contributed to the appearance of the drug in the infant’s blood. Based on this report, the American Academy of Pediatrics considers that sulfasalazine should be given with caution to breastfeeding mothers.

However, continued treatment with sulfasalazine can generally be recommended to breastfeeding mothers of healthy infants. A small study initially involving 17 mother-child pairs concluded sulfasalazine treatment could continue throughout pregnancy and lactation. The study found negligible amounts of sulfasalazine and its primary metabolite, sulfapyridine, were transferred to the child via breastfeeding. The authors did, however, warn that this conclusion could not be applied to a prematurely born child or a child with hemolytic disease.

Effects on the Blood

Blood disorders constitute 19% of all reactions reported with sulfasalazine. As of June 1993, the UK CSM was aware of 191 reports of neutropenia, leucopenia, or agranulocytosis (22 fatal), 44 reports of bone marrow depression or aplastic anemia (13 fatal), and 30 reports of thrombocytopenia (1 fatal).

Although blood dyscrasias were initially thought to be caused by the sulfapyridine moiety, subsequent experience has shown that the aminosalicylates can also cause hematological reactions (see Mesalazine). The risk of blood dyscrasias with sulfasalazine has been estimated at 0.6 per 1000 in those given the drug for inflammatory bowel disease but about ten times greater in patients receiving sulfasalazine for rheumatoid arthritis. Sulfasalazine inhibits folic acid absorption, interferes with its metabolism, and can increase folic acid requirements through hemolysis of red blood cells. These effects are not usually significant in patients with inflammatory bowel disease unless there are additional factors causing folate deficiency, such as intercurrent illness or an exacerbation of bowel disease.

However, clinical folate deficiency with macrocytosis, megaloblastic anemia, or pancytopenia has been reported rarely. Macrocytic anemia associated with sulfasalazine may occur more commonly in patients with rheumatoid arthritis. It was found in 7 of 50 patients within 3 to 4 months of starting treatment with sulfasalazine. The effects of sulfasalazine on folic acid metabolism are dose-related and respond to withdrawal or dosage reduction, and folic acid supplements intravenous folinic acid may sometimes be needed. Although the effects may be potentially severe, they are not a contra-indication to continuing sulfasalazine treatment.

Patients with a history of leucopenia associated with gold therapy for rheumatoid arthritis should not be given sulfasalazine since a similar reaction may occur.

Effects on the Cardiovascular System

Reports include Raynaud’s syndrome with sulfasalazine and myocarditis with sulfasalazine and with mesalazine. Myocarditis leading to fatal cardiogenic shock has been reported in a patient receiving mesalazine, and it has been recommended that glucocorticoids should replace sulfasalazine or mesalazine if cardiac symptoms arise.

Effects on Fertility

Although successful pregnancies have been reported in the partners of men taking sulfasalazine, male infertility is a well-recognized complication of sulfasalazine treatment. Untreated inflammatory bowel disease is not associated with abnormal seminal quality or infertility. Still, oligospermia, reduced sperm motility, and an increase in morphological abnormalities are seen after treatment with sulfasalazine, which may lead to infertility. Oligospermia has been reported in 86% of men with inflammatory bowel disease treated with sulfasalazine.

Seminal characteristics and fertility return to normal within 2 to 3 months of withdrawing sulfasalazine, and successful pregnancies have been reported after withdrawal. The mechanism involved is thought to have a direct toxic effect on immature and developing spermatozoa, possibly due to the sulfapyridine moiety. Improvement in seminal characteristics and successful pregnancies have been reported following the substitution of mesalazine or balsalazide for sulfasalazine in patients with ulcerative colitis. However, reversible infertility, similar to that caused by sulfasalazine, has also been reported with mesalazine.

Effects on the Gastrointestinal Tract

Sulfasalazine-induced exacerbations of ulcerative colitis have been reported and are probably caused by the salicylate moiety rather than sulfapyridine. Other reported effects include intestinal villous atrophy.

Effects on the Hair

Alopecia occurred on two occasions after starting sulfasalazine 2 or 3 g daily in a patient with ulcerative colitis. On both occasions, average hair growth returned after treatment was stopped, and the patient was later successfully desensitized. However, alopecia that developed in another patient during sulfasalazine treatment did not recur on rechallenge. In this case, postpartum alopecia was considered to be the cause, and these authors doubted whether sulfasalazine causes alopecia at all. Hair loss has been reported in 2 patients receiving mesalazine enemas. However, remission of alopecia universalis has been reported during sulfasalazine treatment of rheumatoid arthritis.

Effects on the Kidneys

UK-licensed product information advises that adequate fluid intake and avoidance of urinary acidifiers may reduce the incidence of crystalluria and stone formation. For reports of nephrotic syndrome and of interstitial nephritis associated with sulfasalazine treatment, see under Mesalazine.

Effects on the Pancreas

The UK CSM had received six reports of pancreatitis associated with sulfasalazine as of February 1994. There had been further reports associated with mesalazine. However, a large Danish population-based case-control study concluded neither sulfasalazine nor mesalazine was associated with an increased risk of pancreatitis and that any increased risk might be associated with inflammatory bowel disease itself.

Effects on the Respiratory System

Although one study reviewed 50 cases of sulfasalazine-induced pulmonary complications, pulmonary toxicity remains a rare adverse effect. Most reports include dyspnoea, cough, pulmonary infiltrates, fever, and eosinophilia, usually developing in the first few months of treatment, although they may occur after several years. Symptoms are generally readily reversible on withdrawal of sulfasalazine, although death due to fibrosing alveolitis has been reported, and the need for corticosteroid therapy remains debatable.

These effects have also occurred with mesalazine. They have been reported in patients with a history of sensitivity to salicylates sulfonamides or with no known sensitivity to these drugs. Bronchiolitis obliterans organizing pneumonia has been reported in a patient with rheumatoid arthritis receiving sulfasalazine. Clinical improvement occurred after sulfasalazine was stopped and corticosteroid therapy started.

Effects on Taste

A metallic taste has occurred in patients taking sulfasalazine for ulcerative colitis. However, diseases causing changes in gastrointestinal absorption may lead to zinc deficiency, associated with a metallic taste. There has also been a report of two patients developing a reversible taste dysfunction while taking sulfasalazine for rheumatoid arthritis.


A study in 11 patients with sulfasalazine-induced lupus found that induction of disease was more likely in patients who were slow acetylators of sulfapyridine and who had HLA haplotypes associated with idiopathic SLE. Furthermore, the risk of developing persistent SLE and lupus nephritis increased with the duration of treatment and cumulative dose of sulfasalazine. Lupus-like syndrome has also occurred with mesalazine.


Sulfasalazine has been associated with acute attacks of porphyria and is considered unsafe in porphyric patients.


Sulfasalazine and its sulfapyridine metabolites readily cross the placenta, resulting in similar concentrations in the cord serum and maternal serum at delivery. The concentration of the 5-aminosalicylic acid component of sulfasalazine in both cord serum and maternal serum is negligible. There have been isolated reports of congenital abnormalities associated with the use of sulfasalazine during pregnancy, including coarctation of the aorta with a ventricular septal defect and genito-urinary disorders. There is also a theoretical risk of kernicterus in the neonate if sulfasalazine is given close to delivery.

However, given the concentrations of sulfasalazine and its metabolites found in cord blood, the risk of kernicterus from maternal use is considered minimal. There have been many successful and uncomplicated pregnancies during sulfasalazine therapy, and the consensus favors continuing sulfasalazine throughout pregnancy when indicated. The minimum effective dose should be used, and since sulfasalazine may precipitate folate deficiency (see Effects on the Blood), folic acid supplements are recommended.


Giving sulfasalazine with antibacterial therapy may reduce the conversion of sulfasalazine to its active metabolite (see below).

Sulfasalazine has been reported to interfere with the absorption of digoxin or folic acid (see Effects on the Blood, above) from the gastrointestinal tract.


Since the effects of sulfasalazine depend on the release of 5-aminosalicylic acid by bacterial metabolism in the gut, any drug that reduces the intestinal microflora may reduce the production of the active metabolite. Evidence for this has been seen in patients also given rifampicin and ethambutol} or in subjects also given ampicillin. However, a decrease in clinical effects has not been seen.


For mention of 5-aminosalicylates such as sulfasalazine inhibiting the metabolism of thiopurine antineoplastics and increasing their toxicity, see Mercaptopurine.

Drug Nomenclature

International Nonproprietary Names (INNs) in main languages (French, Latin, Russian, and Spanish):

Synonyms: SI-88; Salatsosulfapyridiini; Salazosulfapyridin; Salazosulfapyridine; Salazosulfapyridinum; Salicylazosulfapyridine; Sulfasalatsiini; Sulfasalazin; Sulfasalazina; Sulfasalazinas; Sulfasalazinum; Sulphasalazine; Szulfaszalazin

BAN: Sulfasalazine

USAN: Sulfasalazine

INN: Sulfasalazine [rINN (en)]

INN: Sulfasalazina [rINN (es)]

INN: Sulfasalazine [rINN (fr)]

INN: Sulfasalazinum [rINN (la)]

INN: Сульфасалазин [rINN (ru)]

Chemical name: 4-Hydroxy-4´-(2-pyridylsulphamoyl)azobenzene-3-carboxylic acid

Molecular formula: C18H14N4O5S =398.4

CAS: 599-79-1

ATC code: A07EC01

Read code: y01R2; y07d3; y00j0 [Musculoskeletal Use]; y07lJ; y08Cd [Gastrointestinal Use]

Pharmacopoeias. In China, Europe, International, Japan, and the US.

European Pharmacopoeia, 6th ed. (Sulfasalazine). A bright yellow or brownish-yellow, fine powder. Practically insoluble in water and dichloromethane, it is very slightly soluble in alcohol and dissolves in dilute solutions of alkali hydroxides. Protect from light.

The United States Pharmacopeia 31, 2008 (Sulfasalazine). A fine, odorless bright yellow or brownish-yellow powder. Practically insoluble in water, chloroform, ether, and benzene, soluble 1 in 2900 of alcohol, and 1 in 1500 of methyl alcohol soluble in aqueous solutions of alkali hydroxides. Store in airtight containers. Protect from light.


British Pharmacopoeia 2008: Sulfasalazine Tablets

The United States Pharmacopeia 31, 2008: Sulfasalazine Delayed-release Tablets; Sulfasalazine Tablets

Proprietary Preparations:

Argentina: Azulfidine Flogostop

Australia: Fyralin Salazopyrin

Austria: Colo-Pleon Salazopyrin

Belgium: Salazopyrine

Brazil: Azulfin Salazoprin

Canada: Salazopyrin SAS

Chile: Azulfidine

Czech Republic: Salazopyrin

Denmark: Salazopyrin

Finland: Salazopyrin

France: Salazopyrine

Germany: Azulfidine Colo-Pleon Pleon PA

Greece: Salopyrine

Hong Kong: Salazopyrin

Hungary: Salazopyrin

India: Saaz Salazar Sazo

Ireland: Salazopyrin

Israel: Salazopyrin

Italy: Salazopyrin

Japan: Azulfidine

Malaysia: Salazopyrin

Mexico: Azulfidina

The Netherlands: Salazopyrine

Norway: Salazopyrin

New Zealand: Salazopyrin

Poland: Salazopyrin

Portugal: Salazopirina

South Africa: Salazopyrin

Singapore: Salazopyrin

Spain: Salazopyrina

Sweden: Salazopyrin

Switzerland: Salazopyrin

Thailand: Salazopyrin Saridine

Turkey: Salazopryn

UK: Salazopyrin Sulazine

USA: Azulfidine

Venezuela: Azulfidine

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