Sulfadiazine

Sulfadiazine is one of the sulfa drugs, typically used as an antibiotic although its use was far more common before the development of penicillin, which has largely replaced it. However, it it still more effective than modern antibiotics in the treatment of several infections, including toxoplasmosis and chlamydia.
Side effects are more severe than with modern antibiotics and include nausea, diarrhea, headache, fever, rash, pancreatitis, and even clinical depression. It should be avoided in pregnant women and is contraindicated if a woman is breastfeeding.
Sulfadiazine at Wikipedia