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Sulfamethoxazole / Trimethoprim


Brand names:

Bactrim®, Septra®, Sulfatrim®

Other names:

SMX-TMP,  Co-trimoxazole

Often used for:


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About Sulfamethoxazole / Trimethoprim

Sulfamethoxazole/Trimethoprim is an antibiotic. It works to kill bacteria that cause infections. Some patients may receive this medicine to prevent pneumonia during chemotherapy. This medicine may also be given to treat infections. Follow dosing instructions carefully.

Patients may have tests to monitor blood counts while receiving this medicine.

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May be taken as a tablet by mouth

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May be taken as a liquid by mouth

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May be given as a liquid into a vein by IV

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Possible Side Effects

  • Nausea and vomiting
  • Rash
  • Sun sensitivity
  • Loss of appetite
  • Diarrhea
  • Abdominal pain
  • Low blood counts

Not all patients who take sulfamethoxazole/trimethoprim will experience these side effects. Common side effects are in bold, but there may be others. Please report all suspected side effects to your doctor or pharmacist.

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Tips for Families

Be sure to discuss these and other recommendations with your doctor or pharmacist.

  • While taking this medicine, it is important to drink plenty of fluids. Patients should follow the care team’s instructions for appropriate fluid intake.
  • This medicine may affect some lab tests.
  • Patients should avoid drinking alcohol while on this medicine.
  • Patients should protect their skin from the sun while taking this medicine.
  • Patients should tell their doctor if they are pregnant, trying to get pregnant, or breastfeeding.
  • Finish all doses of the medicine as instructed by a doctor or pharmacist.

Sulfamethoxazole/Trimethoprim at home:

  • Take medicine at the same time each day.
  • This medicine can be taken with or without food. Take with food if stomach upset occurs.
  • Take medicine with a full glass of water. 
  • Liquid medicine: Shake well, and use the measuring device that comes with the medicine.
  • Store at room temperature. Protect from light.
  • Give a missed dose as soon as possible. If it is near the time of the next dose, skip the dose. Do not give 2 doses at the same time.
  • Do not use the medicine past the expiration date.
  • Follow instructions for safe storage and disposal.