Sulfadoxine

Sulfadoxine (also spelled sulphadoxine) is an ultra-long-lasting sulfonamide used in combination with pyrimethamine to treat malaria. 
It is also used to prevent malaria but due to high levels of resistance, this use is becoming less common.
It is also used, usually in combination with other drugs, to treat or prevent various infections in livestock.
Mechanism of action.
Sulfadoxine competitively inhibits dihydropteroate synthase, interfering with folate synthesis.