Uses

What is sulfamethoxazole/trimethoprim used for?

Sulfamethoxazole/trimethoprim is an antibiotic that is commonly used for the following infections caused by certain bacteria or parasites.

Sulfamethoxazole/trimethoprim may not be appropriate for some of the infections listed above, depending on which bacteria or parasites are causing the infection. Bacteria or parasites in some locations may have developed resistance to sulfamethoxazole/trimethoprim, which will make it less effective.

Sulfamethoxazole/trimethoprim may also be used for other conditions as determined by your healthcare provider.

How does sulfamethoxazole/trimethoprim work (mechanism of action)?

Sulfamethoxazole/trimethoprim kills certain types of bacteria or parasites by blocking their ability to create proteins and other substances that they need to grow and reproduce.

How is sulfamethoxazole/trimethoprim supplied (dosage forms)?

Brands and other names

  • Bactrim and Bactrim DS
  • Septra and Septra DS
  • Sulfatrim

Dosage forms and strengths

  • 200 mg/40 mg per 5 mL oral suspension 
  • 400 mg/80 mg oral tablets
  • 800 mg/160 mg oral tablets

Sulfamethoxazole/trimethoprim is also available in injectable forms.

How should I store sulfamethoxazole/trimethoprim?

Sulfamethoxazole/trimethoprim should be stored at room temperature, between 68 F to 77 F (20 C to 25 C). It can be exposed to temperatures between 59 F to 86 F (15 C to 30 C) for shorter periods of time, such as when transporting it. Store in a cool, dry place. Protect from light.

Side Effects

What are the most common side effects of sulfamethoxazole/trimethoprim?

The most common side effects of sulfamethoxazole/trimethoprim are listed below. Tell your healthcare provider if you have any of these side effects that bother you.

  • Nausea and vomiting
  • Loss of appetite
  • Rash or hives

There may be other side effects of sulfamethoxazole/trimethoprim that are not listed here. Contact your healthcare provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088. In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of sulfamethoxazole/trimethoprim?

While less common, the most serious side effects of sulfamethoxazole/trimethoprim are described below, along with what to do if they happen.

Severe Allergic Reactions. Sulfamethoxazole/trimethoprim may cause allergic reactions, which can be serious. Stop using sulfamethoxazole/trimethoprim and get help right away if you have any of the following symptoms of a serious allergic reaction.

  • Breathing problems or wheezing
  • Cough
  • Racing heart
  • Fever or general ill feeling
  • Low blood pressure
  • Confusion
  • Swollen lymph nodes
  • Swelling of the face, lips, mouth, tongue, or throat
  • Trouble swallowing or throat tightness
  • Itching, skin rash, or pale red bumps on the skin called hives
  • Nausea or vomiting
  • Dizziness, feeling lightheaded, or fainting
  • Pale appearance
  • Yellowing of the skin or eyes
  • Red or purple spots on the skin
  • Stomach cramps
  • Joint pain
  • Chest pain

Severe Skin Reactions. Sulfamethoxazole/trimethoprim can cause severe skin reactions, called Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN), that can lead to death if not treated. If you develop a rash, stop sulfamethoxazole/trimethoprim and call your healthcare provider right away. Get emergency help if you have any of the following symptoms of SJS or TEN.

  • Painful red or purple skin that looks burned and peels off
  • Flat red rash or blisters on your skin, mouth, nose, and genitals
  • Red, painful, watery eyes

Severely Low Platelet Levels. Sulfamethoxazole/trimethoprim can cause you to have a severely low number of platelets in your blood, also called thrombocytopenia. Platelets help to form blood clots. Having a low level of platelets may increase your risk of bleeding. Tell your healthcare provider if you have any of the following symptoms of low platelet levels.

  • Easy bruising or bleeding
  • Bleeding that does not stop
  • Nosebleeds

Antibiotic-associated Diarrhea. An overgrowth of germs called Clostridioides difficile, or “C. diff,” can happen in your gut with many types of antibiotics, including sulfamethoxazole/trimethoprim. This can cause a condition known as antibiotic-associated diarrhea and can happen even up to 2 months after stopping the antibiotic. Call your healthcare provider right away if you have any of the following symptoms of this condition.

  • Watery diarrhea
  • Diarrhea that does not go away
  • Blood in your stool (poop)
  • Severe stomach cramps
  • Fever that starts after you start or finish the medicine

Warnings & Precautions

Who should not use sulfamethoxazole/trimethoprim?

Allergies to Ingredients. People who are allergic to any of the following should not take sulfamethoxazole/trimethoprim.

  • Sulfamethoxazole/trimethoprim
  • Bactrim or Bactrim DS
  • Septra or Septra DS
  • Sulfatrim
  • Any of the ingredients in the specific product dispensed

Your pharmacist can tell you all of the ingredients in the specific sulfamethoxazole/trimethoprim products they stock.

Low Platelets with Previous Sulfamethoxazole/Trimethoprim Use. Sulfamethoxazole/trimethoprim should not be used if you had low platelets while previously taking it. Tell your healthcare provider if you have previously had low platelets while taking sulfamethoxazole/trimethoprim.

Children Less Than 2 Months Old. Sulfamethoxazole/trimethoprim should not be used in children under 2 months of age. Contact your healthcare provider before giving this medicine to your child if he or she is less than two months of age.

Anemia due to Low Levels of Vitamin B-9. Sulfamethoxazole/trimethoprim should not be used if you have anemia, or low red blood cells, due to low levels of vitamin B-9 (also known as folate). If there is concern about you having this condition, your healthcare provider may do tests to determine if you can safely take this medicine.

Liver Problems. Sulfamethoxazole/trimethoprim should not be used if your liver is not working as well as it should be. If there is a concern about the health of your liver, your healthcare provider may do tests to determine if it is working well enough to take this medicine.

Kidney Problems. Sulfamethoxazole/trimethoprim should not be used if your kidneys are not working as well as they should be. If there is a concern about the health of your kidneys, your healthcare provider may do tests to determine if they are working well enough to take this medicine.

Drug Interactions. Sulfamethoxazole/trimethoprim should not be taken while you are using certain other medicines. Before taking sulfamethoxazole/trimethoprim, tell your healthcare provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.  See the Interactions section for more details.

What should I know about sulfamethoxazole/trimethoprim before using it?

Do not take sulfamethoxazole/trimethoprim unless it has been prescribed to you by a healthcare provider. Take it as prescribed. 

Do not share sulfamethoxazole/trimethoprim with other people, even if they have the same condition as you. It may harm them.

Keep sulfamethoxazole/trimethoprim out of the reach of children.

Sulfamethoxazole/trimethoprim can affect your alertness or coordination. Do not drive or do other activities that require alertness or coordination until you know how nitrofurantoin affects you.

Sulfamethoxazole/trimethoprim can make your skin more sensitive to light from the sun, sunlamps, and tanning beds. This is called photosensitivity. Exposure to this light can cause severe sunburns, blisters, and swelling. If you need to be in sunlight, wear sunscreen, a hat, and clothing that covers your skin.

People who are 65 and older can be at greater risk for some side effects from sulfamethoxazole/trimethoprim. Talk to your healthcare provider about your risks if you are in this age group.

For sulfamethoxazole/trimethoprim oral liquid, shake the bottle well before each use and use an accurate measuring device to measure your dose. A household spoon is not an accurate measuring device and may cause you to take the wrong dose. Ask your pharmacist to recommend an appropriate measuring device.

What should I tell my healthcare provider before using sulfamethoxazole/trimethoprim?

Tell your healthcare provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them determine if sulfamethoxazole/trimethoprim is right for you.

In particular, make sure that you discuss any of the following.

Current and Past Health Conditions. Tell your healthcare provider if you have any of the following.

Pregnancy. Sulfamethoxazole/trimethoprim may cause harm to an unborn baby. Tell your healthcare provider if you are or plan to become pregnant. Your healthcare provider will advise you if you should take sulfamethoxazole/trimethoprim while you are pregnant or trying to get pregnant.

Breastfeeding. Sulfamethoxazole/trimethoprim passes into breast milk. Tell your healthcare provider if you are breastfeeding or plan to breastfeed. Your healthcare provider will advise you if you should take sulfamethoxazole/trimethoprim while breastfeeding.

Interactions

Does sulfamethoxazole/trimethoprim interact with foods or drinks?

There are no known interactions between sulfamethoxazole/trimethoprim and foods or drinks.

It is unknown if drinking alcohol will affect sulfamethoxazole/trimethoprim, but heavy drinking can slow your immune response and make it harder for your body to fight infection

Does sulfamethoxazole/trimethoprim interact with other medicines (drug interactions)?

Always tell your healthcare provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss if you are using any of the following before taking sulfamethoxazole/trimethoprim.

  • A diuretic, also called a water pill, which is a medicine used to reduce edema (fluid retention) and blood pressure
  • Warfarin, which is a medicine used to prevent or treat blood clots in the body
  • Phenytoin (Dilantin, Phenytek, and others), which is a medicine to control seizures
  • Methotrexate (Trexall and others), which is a medicine commonly used for rheumatoid arthritis or certain types of cancer
  • Cyclosporine (Gengraf, Neoral, Sandimmune, and others), which is a medicine to suppress your immune system
  • Digoxin (Lanoxin), which is a medicine used to control heart rate
  • Indomethacin (Indocin), which is a medicine used for pain, swelling, and fever
  • Pyrimethamine (Daraprim), which is a medicine used for toxoplasmosis
  • A tricyclic antidepressant, even if it is not used for depression
  • A medicine for diabetes, such as pioglitazone, repaglinide, rosiglitazone, glipizide, glyburide, or metformin
  • Amantadine (Gocovri or Osmolex ER), which is a medicine used for certain nervous system diseases
  • A type of medicine called an angiotensin converting enzyme inhibitor, such as lisinopril (Zestril and others), enalapril (Epaned, Vasotec), benazepril (Lotensin), captopril (APO-Capto and others), quinapril (Accupril), trandolapril (Mavik, Odrik, and others), which is used for blood pressure, heart failure, and kidney disease
  • Zidovudine, which is a medicine used for human immunodeficiency virus (HIV)
  • Dofetilide, which is a medicine used for abnormal heart rhythms 
  • Procainamide, which is a medicine used for abnormal heart rhythms
  • Leucovorin, which is a medicine commonly used in patients with cancer

Sulfamethoxazole/trimethoprim may alter the blood levels of some other medicines. Tell your healthcare provider about all medicines that you take or have recently taken.

This may not be a complete list of medicines that can interact with sulfamethoxazole/trimethoprim. Always check with your healthcare provider.

Does Sulfamethoxazole/Trimethoprim interact with other drugs you are taking?
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Overdose/Missed Dose

What should I do if I accidentally use too much sulfamethoxazole/trimethoprim?

If you or someone else has used too much sulfamethoxazole/trimethoprim, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

What should I do if I miss a dose of sulfamethoxazole/trimethoprim?

If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and only take the next dose. Do not take double or extra doses. 

It is important to complete your prescribed course of sulfamethoxazole/trimethoprim, even if your symptoms get better or go away. This will reduce the risk that future infections are resistant to sulfamethoxazole/trimethoprim or other similar medicines.

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