Sulfadiazine is an antibiotic. Used together with pyrimethamine, a dihydrofolate reductase inhibitor, it is the treatment of choice for toxoplasmosis, which is caused by a protozoan parasite. It is a second-line treatment for otitis media, prophylaxis of rheumatic fever, chancroid, chlamydia, and infections by Haemophilus influenzae. It is also used as adjunct therapy for chloroquine-resistant malaria and several forms of bacterial meningitis. It is taken by mouth. Sulfadiazine is available in multiple generic tablets of 500 mg. For urinary tract infections, the usual dose is 4 to 6 grams daily in 3 to 6 divided doses.