Septra contains two different antibiotics, sulfamethoxazole and trimethoprim. 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 Septra.
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).
Septra 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. Septra should never be used in children under two months old.
On occasion, your healthcare provider may recommend Septra for something other than the conditions discussed in this article. Septra is frequently used
off-label to treat many other types of infections, particularly if they are caused by bacteria that are susceptible to Septra. Also, using the drug to prevent (instead of treat) any type of infection other than
Pneumocystis carinii pneumonia is considered to be an off-label Septra use. Septra is also sometimes used off-label for the treatment of acne.
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