Cotrimoxazole is a fixed-dose combination of trimethoprim and sulfamethoxazole that acts as a bactericidal agent through sequential block of folate metabolism. Trimethoprim inhibits bacterial tetrahydrofolate reductase while sulfamethoxazole inhibits bacterial dihydrofolate reductase. Cotrimoxazole is effective against pathogens like Salmonella typhi, Serratia, Enterobacter, and Klebsiella. It has uses for urinary tract infections, respiratory tract infections, typhoid, bacterial diarrhea, and dysentery. Adverse effects include those related to sulfonamides like megaloblastic anemia and blood dyscrasias.