Sulfadiazine versus sulfafurazole excretion in urine and risk of crystallization in children with conventional dosage regimen.

: The excretion of sulfadiazine (Adiazin) (n = 8) and sulfafurazole (n = 8) in urine and the risk of crystallization were compared in children, 3-14 years of age. They suffered from acute urinary tract infection and were treated with conventional dosage regimen of either of the sulfonamides. Sulfadiazine (4 mg/kg twice daily, the initial dose 8 mg/kg) produced active serum drug levels which in relation to antimicrobial activity of sulphonamides corresponded to 25-30% of those obtained with sulfafurazole (50 mg/kg four times a day). In urine the corresponding sulfadiazine levels were 21-61% of those of sulfafurazole. In none of the urine fractions sulfadiazine concentrations exceeded the theoretical drug solubility but sulfafurazole exceeded this risk limit altogether in 4 urine fractions (2 patients). Urine sediment showed, however, sulfonamide crystals in only one urine fraction of the sulfafurazole group. The results suggest that with conventional dosage regimen sulfafurazole produces higher effective serum and urine drug concentrations in children than sulfadiazine but shows a higher risk to crystallize in urine.