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Sulfamethoxazole/trimethoprim (By mouth)

Sulfamethoxazole (sul-fa-meth-OX-a-zole), Trimethoprim (trye-METH-oh-prim)

Treats or prevents infections. This medicine contains a sulfa drug (sulfonamide).

Brand Name(s):

Bactrim, Bactrim DS, SMZ-TMP Pediatric, Septra, Sulfatrim, Sulfatrim Pediatric

There may be other brand names for this medicine.

When This Medicine Should Not Be Used:

This medicine is not right for everyone. Do not use it if you had an allergic reaction to trimethoprim, sulfamethoxazole, or any sulfa drug. Do not use this medicine if you are pregnant, if you have anemia caused by low levels of folic acid, or if you have a history of drug-induced thrombocytopenia.

How to Use This Medicine:

Liquid, Tablet

  • Take your medicine as directed.
  • Measure the oral liquid medicine with a marked measuring spoon, oral syringe, or medicine cup.
  • Drink extra fluids so you will urinate more often and help prevent kidney problems.
  • Take all of the medicine in your prescription to clear up your infection, even if you feel better after the first few doses.
  • Missed dose: Take a dose as soon as you remember. If it is almost time for your next dose, wait until then and take a regular dose. Do not take extra medicine to make up for a missed dose.
  • Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Do not freeze the oral liquid.

Drugs and Foods to Avoid:

Ask your doctor or pharmacist before using any other medicine, including over-the-counter medicines, vitamins, and herbal products.

  • Some medicines can affect how this medicine works. Tell your doctor if you also use the following:
    • amantadine, cyclosporine, digoxin, indomethacin, memantine, methotrexate, phenytoin, pyrimethamine, or warfarin
    • an ACE inhibitor, diabetes medicine (glipizide, glyburide, metformin, pioglitazone, repaglinide, rosiglitazone), a diuretic (water pill, such as hydrochlorothiazide), or a tricyclic antidepressant

Warnings While Using This Medicine:

  • It is not safe to take this medicine during pregnancy. It could harm an unborn baby. Tell your doctor right away if you become pregnant.
  • Tell your doctor if you are breastfeeding, or if you have kidney disease, liver disease, diabetes, malabsorption or malnutrition, folate deficiency, porphyria, thyroid problems, or a history of alcoholism. Tell your doctor if you have asthma or severe allergies, especially if you are allergic to any medicines. It is important for your doctor to know if you have HIV or AIDS, because this medicine might work differently for you.
  • This medicine may cause a severe allergic reaction.
  • This medicine may lower the number of platelets in your body, which are necessary for proper blood clotting. This may cause you to bleed or get infections more easily. Talk with your doctor if you have concerns about this.
  • This medicine can cause diarrhea. Call your doctor if the diarrhea becomes severe, does not stop, or is bloody. Do not take any medicine to stop diarrhea until you have talked to your doctor. Diarrhea can occur 2 months or more after you stop taking this medicine.
  • Tell any doctor or dentist who treats you that you are using this medicine. This medicine may affect certain medical test results.
  • Your doctor will do lab tests at regular visits to check on the effects of this medicine. Keep all appointments.
  • Keep all medicine out of the reach of children. Never share your medicine with anyone.

Possible Side Effects While Using This Medicine:

Call your doctor right away if you notice any of these side effects:

  • Allergic reaction: Itching or hives, swelling in your face or hands, swelling or tingling in your mouth or throat, chest tightness, trouble breathing
  • Blistering, peeling, or red skin rash
  • Dark urine or pale stools, nausea, vomiting, loss of appetite, stomach pain, yellow skin or eyes
  • Chest pain, cough, or trouble breathing
  • Confusion, weakness
  • Muscle twitching
  • Severe diarrhea, stomach pain, cramps, bloating
  • Skin rash, purple spots on your skin, or very pale or yellow skin
  • Sore throat, fever, muscle pain
  • Uneven heartbeat, numbness or tingling in your hands, feet, or lips
  • Unusual bleeding, bruising, or weakness

If you notice these less serious side effects, talk with your doctor:

  • Mild nausea, vomiting, or loss of appetite

If you notice other side effects that you think are caused by this medicine, tell your doctor

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088


Last Updated: 8/4/2014


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