Sulfasalazine Safety During Lactation

Sulfasalazine (Azulfidine) is considered compatible with breastfeeding and can be safely used by lactating mothers. 1

Evidence for Safety

According to the 2025 EULAR recommendations, sulfasalazine is explicitly listed as compatible with breastfeeding for women with rheumatic and musculoskeletal diseases 1
The 2020 American College of Rheumatology (ACR) guidelines strongly recommend sulfasalazine as compatible with breastfeeding 1
Studies show that sulfasalazine passes into breast milk in only negligible amounts, while its metabolite sulfapyridine appears in milk at approximately 30-60% of maternal serum levels 2, 3

Sulfasalazine itself transfers minimally into breast milk, with insignificant amounts detected in milk 2
The active metabolite sulfapyridine appears in breast milk at about 40% of maternal serum concentration 3
The relative infant dose (infant dose mg/kg/day divided by maternal dose mg/kg/day) is considered safe when below 10%, which is the case for sulfasalazine 1

While sulfasalazine is considered safe, there are isolated reports of bloody stools or diarrhea in breastfed infants whose mothers were taking sulfasalazine 2
Monitor breastfed infants for signs of diarrhea or bloody stools, although a causal relationship between these symptoms and maternal sulfasalazine use has not been definitively established 2
Sulfapyridine has poor bilirubin-displacing capacity, but monitoring the newborn for potential kernicterus is still recommended as a precaution 2

The safety profile applies to term infants without hemolytic disease; caution may be warranted for premature infants or those with hemolytic conditions 4
One case of agranulocytosis has been reported in an infant whose mother was taking both sulfasalazine and prednisone throughout pregnancy, though this is extremely rare 2
Animal studies have shown potential long-term reproductive effects in offspring exposed to sulfasalazine during gestation and lactation, but these findings have not been confirmed in humans 5

For women with rheumatic and musculoskeletal diseases requiring treatment during lactation, sulfasalazine is one of several recommended options 1
Disease control should be maintained with lactation-compatible medications, and sulfasalazine is considered a safe choice for this purpose 1
The benefits of breastfeeding generally outweigh the minimal risks associated with sulfasalazine use during lactation 6

Other medications considered compatible with breastfeeding include hydroxychloroquine, colchicine, azathioprine, cyclosporine, tacrolimus, NSAIDs, and biologic DMARDs 1
If concerns arise about sulfasalazine use during lactation, these alternatives could be considered based on the specific disease being treated 1