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Brand names:

Bactrim®, Septra®, Sulfatrim®

Other names:

Cotrimoxazole, Co-Trimoxazole, SMX-TMP, SMZ-TMP, Sulfamethoxazole-Trimethoprim, Sulfamethoxazole/Trimethoprim, TMP-SMX, TMP-SMZ, Trimethoprim and Sulfamethoxazole, Trimethoprim-Sulfamethoxazole

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What is sulfamethoxazole-trimethoprim?

Sulfamethoxazole-trimethoprim (SMX-TMP) is a medicine used to treat or prevent infections. It is an antibiotic that works to kill bacteria that cause certain types of infections.

SMX-TMP can prevent fatal pneumonia (Pneumocystis carinii) that can occur during chemotherapy. For the medicine to work well, you must take it exactly as instructed.

Routine lab tests may be used to check blood counts.

If given by IV, this medicine can cause tissue damage, blisters, or skin irritation if it leaks from the vein. Tell your care team if you have pain, burning, redness, or swelling around the IV site.

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May be given as a tablet by mouth

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May be given as a liquid by mouth

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May be given into a vein by IV

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Possible side effects

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

Symptoms of an allergic reaction may include rash, hives, itching, chills, fever, headache, muscle ache, shortness of breath, coughing, tightness in the throat, and swelling of the face or neck. 

Not all patients who take sulfamethoxazole-trimethoprim will have these side effects. Common side effects are in bold, but there may be others. Some side effects may be severe. Please report any symptoms or side effects to your doctor or pharmacist. Find more information on side effects.

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Tips for patients and families

Be sure to discuss all questions and instructions with your doctor or pharmacist.

  • Take all doses as instructed. Taking a smaller amount or missing a dose decreases protection. Giving more medicine does not increase protection.
  • To prevent infection, some patients may take SMX-TMP on a specific schedule, such as every Monday, Tuesday, and Wednesday. Other patients may take SMX-TMP every day to treat certain infections. Always give this medicine as directed by your care team.
  • Make sure your child drinks plenty of liquids. Follow your care team’s instructions for fluid intake.
  • This medicine may make skin more sensitive to the sun and your child may sunburn easily. Take steps to protect skin from the sun. Have your child wear sunscreen and protective clothing. Avoid sun exposure when possible.
  • This medicine may affect some lab tests.
  • Before starting this medicine, your child may be tested for low levels of an enzyme called G6PD. A G6PD deficiency can cause anemia (decreased red blood cells) with some medicines.
  • Patients with a sulfa allergy may react to this medication. Notify your doctor if your child has a sulfa allergy before starting this medication.
  • Patients should not drink alcohol while taking this medicine.
  • Rare but serious reactions have happened with this drug. Seek medical care right away if symptoms do not improve or get worse.
  • It is important that patients tell the care team if they are sexually active, pregnant, or breastfeeding.

Sulfamethoxazole-trimethoprim at home:

  • Give this medicine exactly as instructed.
  • This medicine can be taken with or without food. Give with food if stomach upset occurs.
  • Have your child take the medicine with a full glass (8 ounces) of water. 
  • For the oral liquid medicine, shake well before use. Measure doses carefully. Use the measuring device that comes with the medicine.
  • Give a missed dose as soon as possible. If it is near the time of the next dose, skip the missed dose. Do not give 2 doses at the same time.
  • Finish all doses of medicine as instructed by a doctor.
  • Store at room temperature.
  • Some medicines may need to be protected from light. Follow instructions from the pharmacy.
  • Do not use the medicine past the expiration date.
  • Follow instructions for safe handling, storage, and disposal of this medicine.