Generally, the incidence of severe sulfasalazine-induced adverse effects is low, but minor adverse effects occur frequently. Onset of adverse effects generally occurs within a few days to 12 weeks following initiation of sulfasalazine therapy, especially when dosage exceeds 4 g daily.
Clinical experience to date indicates that the incidence of sulfasalazine-induced adverse effects in patients with ulcerative colitis generally is similar to that reported in patients with rheumatoid arthritis, although there is a greater incidence of some reactions. The most frequent adverse effects associated with sulfasalazine therapy in patients with ulcerative colitis are anorexia, headache, nausea, vomiting, gastric distress, and reversible oligospermia.
Other adverse effects reported in patients with ulcerative colitis include pruritus, urticaria, rash, fever, Heinz body anemia, hemolytic anemia, and cyanosis. Adverse effects reported in patients with rheumatoid arthritis receiving sulfasalazine include nausea, dyspepsia, headache, abdominal pain, vomiting, fever, dizziness, stomatitis, rash, pruritus, abnormal liver function test values, leukopenia, and thrombocytopenia; reversible immunoglobulin suppression, rarely accompanied by clinical findings, has been observed in sulfasalazine-treated patients with rheumatoid arthritis.
It appears that there are no drug-induced adverse effects that are specific to patients with rheumatoid arthritis; however, rash occurs more frequently in patients with rheumatoid arthritis than in those with ulcerative colitis, occurring in 13 or 3.3% of patients with rheumatoid arthritis or ulcerative colitis, respectively. Most patients who exhibit adverse effects (except rashes) have serum total sulfapyridine concentrations exceeding 50 mcg/mL. The ability to acetylate sulfasalazine may influence the onset and severity of adverse effects. In one study, 86% of patients exhibiting adverse effects were slow acetylators of sulfapyridine.
GI Effects
Nausea, vomiting, gastric distress, diarrhea, and anorexia occur frequently in patients receiving sulfasalazine. The manufacturers suggest that GI intolerance occurring after the first few doses of sulfasalazine is probably caused by mucosal irritation and may be alleviated by distributing the total daily dose more evenly over the day or by giving enteric-coated tablets; however, there have been no definitive studies comparing toxicity of enteric-coated and uncoated tablets.
Symptoms occurring after the first few days of sulfasalazine therapy are probably due to high serum concentrations of total sulfapyridine and may be alleviated by halving the dose and gradually increasing it over several days. If symptoms persist, the drug should be discontinued for 5-7 days, and therapy reinstituted at a lower daily dosage.
There have been isolated reports of enteric-coated sulfasalazine tablets passing intact through the GI tract of some patients, possibly because of a lack of intestinal esterases capable of disintegrating the enteric coating. Additional enteric-coated tablets should not be administered if this occurs.
Sensitivity Reactions
If a hypersensitivity reaction occurs during sulfasalazine therapy, the drug should be discontinued immediately. Desensitization to sulfasalazine is used when reinstitution of therapy with the drug is considered necessary in a patient who has had a hypersensitivity reaction to the drug; however, desensitization should not be attempted in patients with a history of agranulocytosis, toxic epidermal necrolysis, fibrosing alveolitis, or anaphylactoid reaction while receiving sulfasalazine.
Specialized references should be consulted for specific information on desensitization procedures and dosage. Although various desensitization procedures have been reported to be effective, many regimens use an initial sulfasalazine dosage of 50-250 mg daily which is then doubled every 4-7 days until the desired therapeutic dosage is attained. If symptoms of sensitivity recur, the drug should be discontinued.
Other Adverse Effects
A few cases of pulmonary eosinophilia and at least one fatality from fibrosing alveolitis have been reported in patients receiving sulfasalazine. Sulfasalazine may impart an orange-yellow color to alkaline urine and skin.
Precautions and Contraindications
Sulfasalazine shares the toxic potentials of the sulfonamides, especially sulfapyridine, and the usual precautions of sulfonamide therapy should be observed, including maintenance of adequate fluid intake to reduce risk of crystalluria.In addition to the usual contraindications of sulfonamides, sulfasalazine is contraindicated in patients with intestinal or urinary tract obstructions.
Pediatric Precautions
Safety and efficacy of sulfasalazine in children younger than 2 years of age with ulcerative colitis have not been established. Safety and efficacy of sulfasalazine for the management of polyarticular course juvenile rheumatoid arthritis in children 6-16 years of age is supported by evidence from adequate and well-controlled studies in adults.
Adverse effects observed in children receiving sulfasalazine for the management of juvenile rheumatoid arthritis generally are similar to those observed in adults with rheumatoid arthritis. However, sulfasalazine therapy is associated with a high frequency of serum sickness-like syndrome in children with systemic course juvenile rheumatoid arthritis.
This syndrome, which frequently is severe, presents as fever, nausea, vomiting, headache, rash, and abnormalities in liver function test results. Therefore, use of sulfasalazine in patients with systemic course juvenile rheumatoid arthritis is not recommended.
Mutagenicity and Carcinogenicity
In carcinogenicity studies in rats and mice, an increased incidence of urinary bladder transitional cell papillomas was observed in male rats, an increased incidence of urinary bladder transitional cell papilloma of the kidney was observed in female rats, and an increased incidence of hepatocellular adenoma or carcinoma was observed in male and female mice.
Pregnancy and Fertility
Reproduction studies in rats and rabbits using sulfasalazine dosages up to 6 times the usual human dosage have not revealed evidence of harm to the fetus. Sulfasalazine has been used for the treatment of inflammatory bowel disease, including Crohn’s disease and ulcerative colitis, during pregnancy.
Although fetal abnormalities occasionally have been reported in infants born to women with inflammatory bowel disease who received sulfasalazine alone or combined with corticosteroids during pregnancy, most evidence indicates that sulfasalazine is not associated with a substantial risk of teratogenicity and that the potential benefits of therapy with the drug generally appear to outweigh the possible risks in pregnant women with this disease.
Although most experience with the use of sulfasalazine in pregnancy has been in women with inflammatory bowel disease, safety of the drug in pregnant women with rheumatoid arthritis is not expected to differ from that in inflammatory bowel disease and sulfasalazine therapy generally can be continued in pregnant women with rheumatoid arthritis. Some clinicians consider sulfasalazine the disease-modifying antirheumatic drug (DMARD) of choice in women who are planning to become pregnant or who are pregnant. The risk of sulfasalazine-induced kernicterus in neonates born to women who received the drug during the last trimester appears to be low. Agranulocytosis has been reported in a neonate whose mother received sulfasalazine and corticosteroid therapy throughout pregnancy.
The effect of the drug on subsequent growth development and functional maturation in children whose mothers received sulfasalazine during pregnancy has not been determined. Because there are no adequate and controlled studies to date using sulfasalazine in pregnant women, the drug should be used during pregnancy only when clearly needed.
Impairment of male fertility was observed in reproduction studies in rats using sulfasalazine dosages of 800 mg/kg daily. Oligospermia, abnormal sperm forms, impaired sperm motility, and infertility have occurred in men receiving sulfasalazine; however, these effects appear to be reversible following discontinuance of the drug. These effects appear to be caused by effects of sulfapyridine, not 5-aminosalicylic acid (mesalamine), on sperm maturation.