Health Library

Sulfamethoxazole/trimethoprim (By mouth)

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

Treats or prevents infections.

Brand Name(s):

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

When This Medicine Should Not Be Used:

How to Use This Medicine:

Liquid, Tablet

• Your doctor will tell you how much medicine to use. Do not use more than directed.
• Oral liquid: Measure the oral liquid medicine with a marked measuring spoon, oral syringe, or medicine cup.
• Take all of the medicine in your prescription to clear up your infection, even if you feel better after the first few doses.
• Drink extra fluids so you will urinate more often and help prevent kidney problems.
• 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.

• Do not use this medicine if you are also using dofetilide. Do not use this medicine for Pneumocystis jiroveci pneumonia (PCP) if you are also using leucovorin.
• Some medicines can affect how this medicine works. Tell your doctor if you also use the following:
  • Amantadine, cyclosporine, digoxin, indomethacin, memantine, methotrexate, phenytoin, procainamide, pyrimethamine, warfarin, zidovudine
  • Blood pressure medicine (including an ACE inhibitor)
  • Diabetes medicine (including glipizide, glyburide, metformin, pioglitazone, repaglinide, rosiglitazone)
  • Diuretic (water pill, including acetazolamide, hydrochlorothiazide)
  • Medicine to prevent seizures
  • Medicine to treat depression (including TCAs)

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 diabetes, malabsorption or malnutrition, folate deficiency, G6PD 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 the following problems:
  • Serious skin reactions, including Stevens-Johnson syndrome, toxic epidermal necrolysis, drug reaction with eosinophilia and systemic symptoms (DRESS), acute generalized exanthematous pustulosis (AGEP), or acute febrile neutrophilic dermatosis (AFND)
  • Liver problems
  • Hypoglycemia (low blood sugar)
• This medicine lowers the number of certain blood cells, so you may bleed or bruise more easily. Be careful to avoid injuries.
• 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, red skin rash
• Change in how much or how often you urinate, painful urination, lower back or side pain, blood in the urine
• 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, seizures
• Fainting, dizziness, lightheadedness
• Fast, pounding, or uneven heartbeat
• Numbness, tingling, or burning pain in your hands, arms, legs, or feet
• Severe diarrhea, stomach pain, cramps, bloating
• Skin rash, purple spots on your skin, or very pale or yellow skin
• Sore throat, fever, muscle pain
• Unusual bleeding, bruising, or weakness

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

• Headache

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: 9/6/2024