Folic acid antagonists, including sulphonamides and trimethoprim, target microbial folate metabolism, critical for bacterial cell survival. Sulfamethoxazole and trimethoprim target different parts of the folate synthesis pathway, creating a synergistic effect when combined as co-trimoxazole. These drugs are used to treat a range of infections but can be utilised well in the treatment of urinary tract infections (UTIs) due to their broad-spectrum Gram-positive and Gram-negative activity. However, increasing resistance rates in the UK has severely limited their use and they are no longer recommended first line in the empirical treatment of both uncomplicated and complicated UTIs.