The following abstract presents results of a study conducted by a contract laboratory for the National Toxicology Program. The findings were not evaluated in accordance with the levels of evidence for reproductive or developmental criteria established by NTP in March 2009. The findings and conclusions for this study should not be construed to represent the views of NTP or the U.S. Government.
Sulfamethazine (SM), an antibacterial agent, was tested for its effects on reproduction and fertility in CD-1 mice using the RACB protocol. Data from a two week dose-range-finding study (Task 1) were used to set exposure concentrations for the Task 2 continuous cohabitation study at 0.25, 0.50, and 1.0%. These concentrations produced average estimated daily intakes of nearly equal to 425, 805, and 1450 mg/kg/d.
In the F0 generation, two low dose mice died during Task 2, and 1 middle dose group mouse died; these deaths were not attributed to SM consumption by the study pathologist. Body weights and food consumption were not different across groups during Task 2.
During Task 2, the high dose group delivered nearly equal to 20% fewer litters, and those litters contained nearly equal to 6 live pups, compared to 11 pups in control litters. Adjusted live pup weight was reduced by nearly equal to 10%. Additionally, with the exception of the third litter, all treated groups took 1-8 days longer than the controls to deliver each litter. The effect was greatest at the high dose.
These reproductive effects prompted the conduct of Task 3 to determine the affected sex, using control and high dose mice. Approximately 70% of pairs mated and delivered live pups in all groups in Task 3. The groups containing a treated partner delivered nearly equal to 34-40% fewer pups/litter compared to controls; adjusted pup weight was not affected.
After the delivery of the crossover litter, the F0 control and 1% SM mice were killed and necropsied. Male body weight was not affected by SM consumption, though adjusted liver weight was increased by nearly equal to 35%, and seminal vesicle weight was reduced by nearly equal to 30%. Sperm endpoints were unchanged. Female body weight was reduced by nearly equal to 10%, while adjusted liver weight was increased by nearly equal to 14%. The estrous cycle was not evaluated in these animals.
No second generation evaluation was performed for sulfamethazine.
In summary, consumption of almost 1.5 g/kg/d sulfamethazine by mice increased liver weight, reduced female body weight, and reduced fertility of both males and females. Lower levels of consumption were without effect on fertility.