[1] Common side effects include nausea, vomiting, loss of appetite, and skin rashes.

Mammalian cells, and some bacteria, do not synthesize but require preformed folic acid (vitamin B9); they are therefore insensitive to sulfamethoxazole.

[4] The SMX-TMP combination is on the WHO Model List of Essential medicines as a first-choice treatment for urinary tract infections.

[6][7] The most common side effects of sulfamethoxazole are gastrointestinal disturbances (nausea, vomiting, anorexia) and allergic skin reactions (such as rash and urticaria).

These include Stevens–Johnson syndrome (SJS), toxic epidermal necrolysis, fulminant hepatic necrosis, agranulocytosis, aplastic anemia, and other blood dyscrasias.

Inhibiting the production of dihydrofolate intermediate interferes with the normal bacterial synthesis of folic acid (folate).

[12] Hence, blockage of folate production inhibits the folate-dependent metabolic processes for bacterial growth.

Its Tmax (or time to reach maximum drug concentration in plasma) occurs 1 to 4 hours after oral administration.

[8] However, the half-life of the drug noticeably increases in people with creatinine clearance rates equal to or less than 30 mL/minute.