Used primarily to treat bacterial infections, especially urinary tract infections, respiratory infections, and ear infections. It works by inhibiting bacterial folic acid synthesis, which is essential for DNA and protein production in bacteria. Commonly combined with sulfamethoxazole to enhance effectiveness, this combination is also used to prevent and treat Pneumocystis jirovecii pneumonia, particularly in immunocompromised patients such as those with HIV/AIDS. Its selective action against bacterial enzymes makes it effective with minimal impact on human cells.