Bactrim, Bactrim Ds

Written by Malini Ghoshal, RPh, MS
Medically reviewed by Melissa Badowski, PharmD, MPH, FCCP
Updated on June 28, 2023

Specifically, the Food and Drug Administration (FDA) has approved sulfamethoxazole/trimethoprim to treat certain types of bacterial infections, including:

• urinary tract infection (UTI)
• acute otitis media (ear infection) in certain children
• chronic bronchitis
• shigellosis
• pneumocystis pneumonia
• traveler’s diarrhea

These approved uses differ based on the form of sulfamethoxazole/trimethoprim your doctor prescribes.

This article describes sulfamethoxazole/trimethoprim’s uses, side effects, and more.

Sulfamethoxazole/trimethoprim may cause mild or serious side effects. More common mild side effects of sulfamethoxazole/trimethoprim and its serious side effects are listed below. This article doesn’t include all possible side effects of the drug. Side effects can vary based on your age, overall health, and any other medications you take.

To learn more about sulfamethoxazole/trimethoprim’s side effects, ask your doctor or pharmacist. You can also refer to the prescribing information for sulfamethoxazole/trimethoprim listed in the “Article resources” section.

Mild side effects

More common mild side effects reported with some forms of sulfamethoxazole/trimethoprim are listed below. These side effects may differ based on the form of sulfamethoxazole/trimethoprim you’re prescribed.

This article doesn’t include all possible mild side effects of the drug. To learn more about sulfamethoxazole/trimethoprim’s side effects based on the form, refer to the prescribing information for sulfamethoxazole/trimethoprim listed in the “Article resources” section.

With many drugs, mild side effects may go away within a few days or a couple of weeks. If the side effects are bothersome, tell your doctor or pharmacist. They may be able to suggest ways to manage them.

Sulfamethoxazole/trimethoprim’s mild side effects include:

• nausea or vomiting
• loss of appetite
• itching
• rash
• mild allergic reaction*

* For details about this side effect, see the “Interactions and warnings for sulfamethoxazole/trimethoprim” section.

Serious side effects

Serious side effects of sulfamethoxazole/trimethoprim are listed below. These side effects may differ based on the form of sulfamethoxazole/trimethoprim you’re prescribed.

This article doesn’t include all possible serious side effects of the drug. To learn more about sulfamethoxazole/trimethoprim’s side effects based on the form, refer to the prescribing information for sulfamethoxazole/trimethoprim listed in the “Article resources” section.

With many drugs, serious side effects are possible but not common. If you have serious side effects from this drug, call your doctor right away. If you’re having severe symptoms or a medical emergency, call 911 or a local emergency number.

In general, sulfamethoxazole/trimethoprim’s serious side effects include:

• liver failure
• serious blood disorders, including agranulocytosis, aplastic anemia, and thrombocytopenia
• Clostridioides difficile infection (C. diff) diarrhea
• lung injury
• hepatitis
• kidney failure
• low or no urine output
• very low blood sugar
• hallucinations
• depression
• pancreatitis (inflammation of the pancreas)
• hypothyroidism (low levels of thyroid hormones in the blood)
• aseptic meningitis (inflammation of the tissues surrounding the brain and spinal cord)
• convulsions
• rhabdomyolysis (muscle tissue breakdown)
• heart problems, including long QT syndrome and torsades de pointe
• high blood potassium level
• low blood sodium level
• severe headache
• severe allergic reaction*

* For details about this side effect, see the “Interactions and warnings for sulfamethoxazole/trimethoprim” section.

The Food and Drug Administration (FDA) approves prescription drugs such as sulfamethoxazole/trimethoprim for certain conditions. Approved uses for sulfamethoxazole/trimethoprim are described below. These uses differ based on the form of sulfamethoxazole/trimethoprim prescribed.

Use for certain bacterial infections

Doctors may prescribe sulfamethoxazole/trimethoprim oral tablet and oral liquid suspension for:

• urinary tract infection (UTI) in adults and children ages 2 months and older
• acute otitis media (ear infection) in children ages 2 months and older
• chronic bronchitis in adults
• shigellosis in adults and children ages 2 months and older
• pneumocystis pneumonia in adults and children ages 2 months and older
• traveler’s diarrhea in adults

It’s usually prescribed as a short-term treatment for certain types of bacterial infections that sulfamethoxazole/trimethoprim can help prevent or treat.

Doctors may prescribe sulfamethoxazole/trimethoprim liquid solution for injection for treating:

• severe urinary tract infection (UTI)
• pneumocystis pneumonia
• shigellosis

It’s prescribed for these purposes in adults and children ages 2 months old and older. It is usually prescribed as a short-term treatment.

Sulfamethoxazole/trimethoprim liquid solution for injection is given by intravenous (IV) infusion by a healthcare professional. (An IV infusion is an injection given slowly into a vein over time.)

Doctors may not prescribe sulfamethoxazole/trimethoprim in certain situations, such as when:

• you’re allergic to the medication or any of its ingredients
• you have serious liver or kidney disease
• you have folic acid deficiency anemia
• you have thyroid problems

Below, you’ll find information about sulfamethoxazole/trimethoprim’s possible interactions and warnings.

Interactions of sulfamethoxazole/trimethoprim

Certain things may affect how a drug works. These include getting vaccines, consuming alcohol or certain foods, or taking oral dosage forms of the drug with other medications. This effect is called a drug interaction.

Before you take or receive sulfamethoxazole/trimethoprim, ask your doctor to check for possible interactions. Be sure to tell them about any of the following you take or use:

• prescription or over-the-counter drugs
• vitamins, herbs, or supplements

To learn about drug-condition interactions, see the “Warnings for sulfamethoxazole/trimethoprim” section below.

Warnings for sulfamethoxazole/trimethoprim

Some people should not take sulfamethoxazole/trimethoprim tablet or suspension, and others should take the form they’re prescribed cautiously.

Your doctor will discuss whether you can receive sulfamethoxazole/trimethoprim injection as an intravenous (IV) infusion. (An IV infusion is an injection given slowly into a vein over time by a healthcare professional.)

Sulfamethoxazole/trimethoprim could cause harm to people with certain health conditions. This effect is called a drug-condition interaction. Other factors can also affect whether sulfamethoxazole/trimethoprim is a safe option for you. These warnings may differ based on the form of sulfamethoxazole/trimethoprim you’re prescribed.

Ask your doctor about specific warnings for sulfamethoxazole/trimethoprim, and be sure to tell them about your:

• current health, including any allergies to medications
• past health conditions or surgeries

Allergic reaction

Sulfamethoxazole/trimethoprim can cause an allergic reaction in some people. Severe allergic reactions are rare but possible.

If you’ve had an allergic reaction to sulfamethoxazole/trimethoprim or any of its ingredients, your doctor will likely not prescribe sulfamethoxazole/trimethoprim. They can tell you about medications that are safer options for you.

A mild allergic reaction may cause the following symptoms:

• skin rash
• itchiness
• flushing (temporary warmth, redness, or deepening of skin color)

A severe allergic reaction may cause the following symptoms:

• swelling under your skin, usually in your hands, feet, eyelids, or lips
• swelling of your mouth, throat, or tongue, which can cause breathing problems
• severe skin rash, blistering, peeling, or lesions

Examples of severe allergic reactions may include:

• anaphylaxis
• Stevens-Johnson syndrome (severe skin rash)
• toxic epidermal necrolysis (severe skin peeling and blistering)
• drug rash with eosinophilia and systemic symptoms
• acute febrile neutrophilic dermatosis (skin rash that causes bumps and lesions)

If you have an allergic reaction to sulfamethoxazole/trimethoprim, call your doctor right away. If you have severe symptoms, call 911 or a local emergency number.

Overdose of sulfamethoxazole/trimethoprim

If you take sulfamethoxazole/trimethoprim by mouth, you should not take more sulfamethoxazole/trimethoprim than your doctor prescribes. For some drugs, doing so may lead to harmful effects or overdose.

If you think you’ve taken too much sulfamethoxazole/trimethoprim, call your doctor or pharmacist right away. Or you could call 800-222-1222 to speak with someone at America’s Poison Centers. You can also use its online resource. If you have concerning symptoms, call 911 or a local emergency number immediately. You can also go to the closest emergency room.

Pregnancy or breastfeeding and sulfamethoxazole/trimethoprim

Information about sulfamethoxazole/trimethoprim and pregnancy and breastfeeding is described below.

Sulfamethoxazole/trimethoprim and pregnancy

Sulfamethoxazole/trimethoprim may not be safe to take during pregnancy. If you’re planning a pregnancy or can become pregnant, talk with your doctor. They can tell you more about the safety of various dosage forms of sulfamethoxazole/trimethoprim.

Sulfamethoxazole/trimethoprim and breastfeeding

It’s not known whether sulfamethoxazole/trimethoprim should be taken while breastfeeding. The drug passes into breast milk and is not safe for infants younger than 2 months of age. If you’re currently breastfeeding or planning to do so, talk with your doctor before taking this medication. They can tell you whether the dosage form you’re prescribed is safe during breastfeeding.

Below you’ll find answers to a few commonly asked questions about sulfamethoxazole/trimethoprim.

What brand names are available for sulfamethoxazole/trimethoprim?

Brand names available for sulfamethoxazole/trimethoprim oral tablet include:

• Bactrim, Bactrim DS
• Septra, Septra DS

If you have questions about brand-name versions of sulfamethoxazole/trimethoprim, talk with your doctor or pharmacist. They can tell you more about how brand names compare with generic versions of the drug.

How does sulfamethoxazole/trimethoprim work? And how long does it take to start working?

Sulfamethoxazole/trimethoprim is an antimicrobial (antibiotic) that works by killing certain susceptible types of bacteria.

How long it takes sulfamethoxazole/trimethoprim to work depends on the dosage form you’re prescribed and the severity of your infection.

Sulfamethoxazole/trimethoprim oral tablet and oral suspension start to work within 1–4 hours after you take a dose. But it may take a few days for your symptoms to ease.

Sulfamethoxazole/trimethoprim liquid solution for injection is given slowly into a vein over 60–90 minutes. It starts to work soon after it’s given.

Follow your doctor’s directions on taking the oral dosage forms of the medication. Do not stop taking the medication even if you start to feel better. This can cause your condition to worsen or your infection to become resistant to sulfamethoxazole/trimethoprim.

If you’d like to know more about this, talk with your doctor or pharmacist.

This article describes sulfamethoxazole/trimethoprim’s uses and side effects, ways to save on cost, and more. Let your doctor know if you have questions about sulfamethoxazole/trimethoprim or would like more details about it.

Here’s a list of some questions you may want to ask your doctor:

• Does my dosage of sulfamethoxazole/trimethoprim depend on the infection it’s being prescribed to treat or help prevent?
• Would I need another antibiotic if I still have symptoms after taking sulfamethoxazole/trimethoprim for the full course?
• What medications should I avoid while taking sulfamethoxazole/trimethoprim?

• Food and Drug Administration. (2023). Orange Book: Approved drug products with therapeutic equivalence evaluations. https://www.accessdata.fda.gov/scripts/cder/ob/index.cfm
• Sulfamethoxazole and trimethoprim injection, for intravenous use. (2022). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/b89b5502-ce87-45a6-a43c-9891da3cfca4/spl-doc
• Sulfamethoxazole and trimethoprim oral suspension, USP 200mg/40mg per 5mL. (2023). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/5ff03694-787a-409d-a95e-8422aa27499c/spl-doc
• Sulfamethoxazole and trimethoprim tablets, USP. (2023). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/a56a7056-c72a-4e25-9c41-327f429e7af0/spl-doc

Disclaimer: Optum Perks has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.