Most commonly used as a fixed combination of sulphamethoxazole and trimethoprim (TMP/SMX, Bactrim® and Septra®) in the therapy of urinary tract infections, their use has waned as resistance in E. coli has risen. Trimethoprim alone (Proloprim®) is available, has a better adverse effect profile but is more expensive than TMP/SMX. Unlike Canada, in some countries it is commonly utilized.
These agents are sometimes used in the therapy of serious hospital Gram-negative bacilli infections when resistance or intolerance to other agents is an issue. TMP/SMX is also used for the therapy of Pneumocystis jiroveci (carinii) pneumonia and infections caused by the relatively-rare pathogen Stenotrophomonas maltophilia.