Sulfamethoxazole/trimethoprim contains two different antibiotics. Trimethoprim does not belong to a specific class of medications. Sulfamethoxazole belongs to a group of drugs known as sulfonamides ("sulfa" drugs). These two antibiotics work in different but similar ways. Essentially, both sulfamethoxazole and trimethoprim work by inhibiting the production of
folic acid in bacteria, although they work in different stages of folic acid production. Folic acid is important for making proteins and DNA. Because humans obtain folic acid from the diet (and bacteria cannot), human cells are less affected by sulfamethoxazole/trimethoprim.
Combining sulfamethoxazole with trimethoprim increases the effectiveness of the drugs and decreases the chance of antibiotic resistance (the development of bacteria with the ability to resist antibiotics).
Can It Be Used in Children?
Sulfamethoxazole/trimethoprim is approved to treat
urinary tract infections,
ear infections, shigellosis, and
Pneumocystis carinii pneumonia in children at least two months old. It is also approved for
Pneumocystis carinii pneumonia prevention in children at least two months old. Sulfamethoxazole/trimethoprim should never be used in children under two months old.
On occasion, your healthcare provider may recommend sulfamethoxazole/trimethoprim for something other than the conditions discussed in this article. Sulfamethoxazole/trimethoprim is frequently used
off-label to treat many other types of infections, particularly if they are caused by bacteria that are susceptible to sulfamethoxazole/trimethoprim. Also, using the medication to prevent (instead of treat) any type of infection other than
Pneumocystis carinii pneumonia is considered to be an off-label sulfamethoxazole/trimethoprim use. The drug is also used sometimes for the treatment of acne.
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