Disposition of salicylazosulfapyridine (Azulfidine) and metabolites in human breast milk.

A nursing mother with ulcerative colitis was treated with salicylazosulfapyridine (SASP, Azulfidine). Multiple milk samples were collected over a 2-month period. Maternal plasma, saliva, urine and nursing infant's urine were collected. All fluids were analyzed for SASP and its metabolites. Milk did not contain SASP or its 5-amino salicylate component. Sulfapyridine (SP) and its metabolites were present in milk; the SP level was fairly constant at 3--6 micrograms/ml. The milk/saliva ratio for SP was 0.81; the milk/plasma ratio for SP was 0.60 and 0.63. Assuming an average milk concentration of 5 micrograms/ml of SP, the estimated 24-hour secretion (800 cm3 milk) would be approximately 4 mg or 0.3% of maternal dose of SP in the form of SASP. The levels of SP and metabolites determined in random urine samples from the infant were 3--4 micrograms/ml or a 24-hour excretion of 1.2--1.6 mg (30--40% of the total dose in milk). This exposure did not seem hazardous to this infant.