Oversaturation of urine with sulphadiazine during treatment with a small therapeutic dose

The urinary crystallization of N1-pyrimid-2-yl-sulfanilamide (sulphadiazine, Sulfolex) during treatment with a small therapeutic dose (600 mg/day p.o.) for 6 days was evaluated in seven voluntary female subjects. In 5/7 and 3/7, respectively, of the urine supernatants obtained from samples collected 6 and 24 h after the last dose of sulphadiazine, the sulphonamide concentration exceeded the experimental solubility of the drug in 37 degrees C urine at the same pH. However, only in 3 sediments of the 6-h urine samples could a few sulphadiazine crystals be found. The findings suggest that the urine often can be oversaturated in respect to sulphadiazine, without any marked crystallization.