How Does It Work?

Sulfamethoxazole/trimethoprim, as the name implies, 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 and decreases the chance of antibiotic resistance (the development of bacteria with the ability to resist antibiotics).

When and How to Take Sulfamethoxazole/Trimethoprim

Some general considerations include the following:
  • Sulfamethoxazole/trimethoprim comes in tablet or oral suspension (liquid) form. It is taken by mouth, usually twice a day (although it is taken as frequently as four times daily or as infrequently as once daily for certain uses).
  • Sulfamethoxazole/trimethoprim can be taken at any time of the day; however, be sure to take the medication at the same time(s) each day. For instance, if you take it twice daily, it is best to evenly space the doses, taking a dose every 12 hours.
  • Be sure to shake the suspension well just before each dose. It is best to use a measuring device such as a medication spoon or syringe, which are more accurate than kitchen spoons.
  • You can take this medication with food or on an empty stomach. If it bothers your stomach, try taking it with food.
  • For the medication to work properly, it must be taken as prescribed. Sulfamethoxazole/trimethoprim will not work if you stop taking it too soon.
7 Easy Tips for Starting Solids

Sulfamethoxazole Trimethoprim Information

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