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sulfamethoxazole/trimethoprim

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Brand names: Bactrim, Septra

Sulfonamide Antibiotic Combination Rx

Sulfamethoxazole and trimethoprim is a combination antibiotic. It is used to treat bacterial infections.

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What it does

This medicine can treat urinary tract infections, ear infections, bronchitis, and traveler's diarrhea.

Common side effects

Nausea, Vomiting, Loss of appetite

Key warnings

Rarely, this medicine has caused severe reactions, including Stevens-Johnson syndrome and liver damage, which can be deadly.

How It Works

This medicine contains two drugs that work together to kill bacteria. Sulfamethoxazole and trimethoprim both stop bacteria from making folic acid. Bacteria need folic acid to grow and multiply.

How to Take It

Take this medicine exactly as your doctor tells you. Adults usually take 1 double strength tablet or 2 regular tablets every 12 hours. Children's doses are based on weight. You can take it with or without food.

Pregnancy & Breastfeeding

Tell your doctor if you are pregnant or plan to become pregnant. This medicine may not be safe for your baby. Talk to your doctor about breastfeeding while taking this medicine.

Missed Dose

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 continue with your regular schedule.

Storage

Store at room temperature, away from light and moisture.

Side Effects (from patient reports)

Based on 46,278 FDA adverse event reports.

Fever
6,174
Using the medicine for something it's not approved for
5,424
Tiredness
5,208
Diarrhea
4,754
Feeling sick to your stomach
4,728
Skin rash
4,365
Difficulty breathing
4,280
Pain
4,012
Throwing up
3,675
Medicine not working
3,658

Serious Warnings

Rarely, this medicine has caused severe reactions, including Stevens-Johnson syndrome and liver damage, which can be deadly. Tell your doctor right away if you have a fever, rash, blisters, mouth sores, or yellowing of your skin or eyes.

Common Questions

Can I drink alcohol while taking this medicine?
Ask your doctor or pharmacist. Alcohol may worsen some side effects.
How long should I take this medicine?
Take this medicine for the full number of days that your doctor prescribes it. Do not stop early, even if you feel better.
What should I do if I have diarrhea?
Tell your doctor if you have diarrhea, especially if it is severe or bloody. This medicine can sometimes cause a serious type of diarrhea.
Can this medicine interact with other medicines I am taking?
Yes, this medicine can interact with other medicines. Tell your doctor about all the medicines you take, including prescription and over-the-counter medicines, vitamins, and herbal supplements.
What if I am allergic to sulfa drugs?
Tell your doctor if you are allergic to sulfa drugs. This medicine contains a sulfa drug, so you should not take it if you are allergic.
Can this medicine cause sun sensitivity?
Yes, this medicine can make your skin more sensitive to the sun. Wear protective clothing and sunscreen when you are outside.
Is it okay to drive while taking this medication?
This medicine can cause dizziness or drowsiness. Do not drive or operate machinery until you know how this medicine affects you.
What if I feel worse after starting this medicine?
Tell your doctor if your symptoms get worse or if you develop new symptoms.
Can I take this medication if I have kidney problems?
Tell your doctor if you have kidney problems. Your dose may need to be adjusted.
Can this medication be used for a viral infection?
No, this medicine is an antibiotic and only works for bacterial infections. It will not work for viral infections like the common cold or flu.
What are the common side effects of sulfamethoxazole/trimethoprim?
The most commonly reported side effects of sulfamethoxazole/trimethoprim include Nausea, Vomiting, Loss of appetite, Skin rash. Based on 46,278 FDA adverse event reports. Always consult your healthcare provider about potential side effects.
What drug class is sulfamethoxazole/trimethoprim?
sulfamethoxazole/trimethoprim belongs to the Sulfonamide Antibiotic Combination drug class. It requires a prescription (Rx). This medicine can treat urinary tract infections, ear infections, bronchitis, and traveler's diarrhea.
Is sulfamethoxazole/trimethoprim safe during pregnancy?
Tell your doctor if you are pregnant or plan to become pregnant. This medicine may not be safe for your baby. Always consult your healthcare provider before using any medication during pregnancy or breastfeeding.

Related Medications in Sulfonamide Antibiotic Combination

Other drugs grouped near sulfamethoxazole/trimethoprim — same-class peers and common alternatives.

amikacin

Amikin

Amikacin is an antibiotic medicine.

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amoxicillin

Amoxil

Amoxicillin and Clavulanate Potassium is a combination medicine used to fight bacterial infections.

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amoxicillin/clavulanate

Augmentin

Augmentin is a combination of two medicines, amoxicillin and clavulanate.

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ampicillin/sulbactam

Unasyn

Unasyn is a combination of two antibiotics that fights bacteria in your body.

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azithromycin

Zithromax, Z-Pack

Azithromycin is an antibiotic that fights bacteria.

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Compare sulfamethoxazole/trimethoprim vs amikacin side-by-side →

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What the FDA Data Shows for sulfamethoxazole/trimethoprim

The FDA label for sulfamethoxazole/trimethoprim (sold under brand names such as Bactrim, Septra) classifies it as a prescription-only medication in the Sulfonamide Antibiotic Combination class. This medicine can treat urinary tract infections, ear infections, bronchitis, and traveler's diarrhea. Official labeling lists 4 commonly reported side effects, including Nausea, Vomiting, Loss of appetite.

Post-market surveillance from the FDA Adverse Event Reporting System (FAERS) captures real-world experience. For this drug, FAERS contains 46,278 voluntary reports. Interaction data is drawn directly from FDA-approved prescribing information. Acquisition-cost data is surveyed weekly by CMS and updated as manufacturers report changes.

Report counts do not establish causation — a FAERS entry documents a temporal association, not proof that the drug produced the outcome. Widely prescribed medications naturally accumulate more reports than niche therapies, so raw totals must be interpreted alongside total exposure. Shortage status, recall history, and patent information further shape supply and switching decisions. This page summarizes public FDA data for educational purposes only and is not a substitute for professional medical advice — always consult a licensed healthcare provider before starting, stopping, or changing any medication.

Data Sources

Drug labeling: FDA Drug Labels (SPL/DailyMed). Adverse events: FDA Adverse Event Reporting System (FAERS).

FAERS reports are voluntary and do not establish causation. Drug interactions are derived from FDA labeling and clinical references. Always consult a healthcare professional before making medication decisions.

Last updated: October 9, 2022

Read our methodology — how this data is sourced, computed, and verified.

All federal data sources used on this page