An Overview of Sulfamethoxazole-Trimethaprim (Bactrim, Septra, Sulfatrim)

Other Name(s): Bactrim, Bactrim DS, SMX-TMP, Septra, Sulfamethoprim, Sulfamethoprim-DS, Sulfatrim, TMP-SMX
Drug Class: Opportunistic Infections and Coinfections

What Is Sulfamethoxazole/Trimethoprim?

Sulfamethoxazole/trimethoprim is an antibacterial prescription combination medicine approved by the U.S. Food and Drug Administration (FDA) to treat certain infections, such as:

  • Acute exacerbations (worsening) of chronic bronchitis;
  • Urinary tract and acute ear infections;
  • Shigellosis;
  • Diarrhea;
  • Pneumocystis carinii pneumonia (PCP).

Sulfamethoxazole/trimethoprim is also FDA-approved to prevent PCP in people who are immunosuppressed and are at risk of developing PCP.

Shigellosis and PCP are opportunistic infections. An opportunistic Infection is an infection that occurs more frequently or is more severe in people with weakened immune systems -- such as those infected with HIV -- than in people with healthy immune systems. To learn more about opportunistic infections, read the AIDS_info_ What is an Opportunistic Infection? fact sheet.

Sulfamethoxazole/trimethoprim can also be used "off-label" to prevent and treat other opportunistic infections of HIV infection. "Off-label" use refers to use of an FDA-approved medicine in a manner different from that described on the medicine label. Good medical practice and the best interests of a patient sometimes require that a medicine be used "off-label."

What HIV-Related Opportunistic Infections Is Sulfamethoxazole/Trimethoprim Used For?

The Guidelines for the Prevention and Treatment of Opportunistic Infections in HIV-Infected Adults and Adolescents, prepared by the Centers for Disease Control and Prevention (CDC), the National Institutes of Health (NIH), and the HIV Medicine Association of the Infectious Diseases Society of America (IDSA-HIVMA), includes recommendations on the HIV-related uses of sulfamethoxazole/trimethoprim to:

  • Prevent:

    • PCP from occurring the first time (called primary prophylaxis) and from recurring (called secondary prophylaxis or maintenance therapy).
    • Toxoplasma gondii encephalitis (also called toxoplasmosis). (This is an "off-label" use.)
    • Isosporiasis (also called Isospora belli infection) from recurring. (This is an "off-label" use.)
  • Treat:

    • PCP.
    • Toxoplasma gondii encephalitis. (This is an "off-label" use.)
    • Certain bacterial enteric infections, including shigellosis and salmonellosis (also known as Salmonella infection).
    • Isosporiasis. (This is an "off-label" use.)

The above list may not include all of the HIV-related uses of sulfamethoxazole/trimethoprim recommended in the Guidelines for the Prevention and Treatment of Opportunistic Infections in HIV-Infected Adults and Adolescents. Some recommended uses, such as uses in certain rare circumstances, may have been omitted.

What Should I Tell My Health Care Provider Before Taking Sulfamethoxazole/Trimethoprim?

  • If you are allergic to sulfonamides (including sulfamethoxazole), trimethoprim, or any other medicines.
  • About any medical conditions you have or have had, for example, diabetes or liver problems.
  • About anything that could affect your ability to take medicines, such as difficulty swallowing pills, difficulty remembering to take pills, or any health conditions that may prevent your use of intravenous medicines.
  • If you are pregnant or plan to become pregnant. Whether sulfamethoxazole/trimethoprim can harm an unborn baby is unknown. Sulfamethoxazole/trimethoprim should not be used by pregnant women because sulfonamides (including sulfamethoxazole) may cause kernicterus. Talk to your health care provider about possible risks with taking sulfamethoxazole/trimethoprim when pregnant.
  • If you are breastfeeding or plan to breastfeed. Do not breastfeed if you are infected with HIV.
  • About other prescription and nonprescription medicines, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Sulfamethoxazole/trimethoprim may affect the way other medicines or products work, and other medicines or products may affect how sulfamethoxazole/trimethoprim works. Ask your health care provider if there are interactions between sulfamethoxazole/trimethoprim and the other medicines you take.

Ask your health care provider about possible side effects from sulfamethoxazole/trimethoprim. Your health care provider will tell you what to do if you have side effects.

How Should I Take Sulfamethoxazole/Trimethoprim?

Take sulfamethoxazole/trimethoprim according to your health care provider's instructions. Your health care provider will tell you how much sulfamethoxazole/trimethoprim to take and when to take it. Before you start sulfamethoxazole/trimethoprim and each time you get a refill, read any printed information that comes with your medicine.

How should sulfamethoxazole/trimethoprim be stored?

  • Store sulfamethoxazole/trimethoprim oral suspension at room temperature, 68°F to 77°F (20°C to 25°C). Protect the oral suspension from light.
  • Store sulfamethoxazole/trimethoprim tablets at room temperature, 68°F to 77°F (20°C to 25°C).
  • Store sulfamethoxazole/trimethoprim injection solution at room temperature, 68°F to 77°F (20°C to 25°C). Do not refrigerate the injection solution.
  • Do not use sulfamethoxazole/trimethoprim if the original seal of the container is broken or missing.
  • Throw away sulfamethoxazole/trimethoprim that is no longer needed or expired (out of date). Follow FDA guidelines on how to safely dispose of unused medicine.
  • Keep sulfamethoxazole/trimethoprim and all medicines out of reach of children.

Where Can I Find More Information About Sulfamethoxazole/Trimethoprim?

More information about sulfamethoxazole/trimethoprim is available:

The above Patient Version drug summary is based on the following FDA label(s): Injection; Suspension; Tablet, tablet (double strength).