Bactrim (sulfamethoxazole / trimethoprim): Basics, Side Effects & Reviews
Bactrim (sulfamethoxazole / trimethoprim)

Bactrim, Septra (sulfamethoxazole/trimethoprim)

Basics, Side Effects, Reviews & More

Bactrim (sulfamethoxazole / trimethoprim) is good for treating many bacterial infections and is available as a cheap generic. However, a lot of people are allergic to it.


Bactrim, Septra, Bactrim DS, Septra DS, Sulfatrim Pediatric


Sulfonamide Antibiotic


Not a controlled medication


Lower-cost generic available


Prescription only

Reviewed by:

Christina Aungst, PharmD

Allison Barnes, PharmD

Last reviewed on:

September 29, 2020


What is Bactrim (sulfamethoxazole / trimethoprim)?

How Bactrim (sulfamethoxazole / trimethoprim) works

Bactrim (sulfamethoxazole / trimethoprim) is an antibiotic that combines sulfamethoxazole and trimethoprim. The two medications work together to stop a chemical that some bacteria make in order to grow. Once the chemical is stopped, the bacteria stop growing and reproducing.

What is Bactrim (sulfamethoxazole / trimethoprim) used for?

  • Urinary tract infection
  • Traveler's diarrhea in adults
  • Middle ear infections in children
  • Chronic bronchitis flare-ups in adults
  • Pneumonia in people with compromised immune systems
  • Pneumonia prevention in people with compromised immune systems
  • Shigellosis (fever and diarrhea caused by Shigella bacteria)

Bactrim (sulfamethoxazole / trimethoprim) dosage forms

Typical dosing for Bactrim (sulfamethoxazole / trimethoprim)

  • Urinary tract infections, Shigellosis, and Middle ear infections: The typical dose of Bactrim (sulfamethoxazole / trimethoprim) for adults is 800 mg/160 mg (sulfamethoxazole/trimethoprim) taken by mouth every 12 hours for 5 to 14 days. The length of time you take Bactrim (sulfamethoxazole / trimethoprim) for depends on the type of infection you have and how bad it is. The dose given to children is based on their weight and is taken by mouth every 12 hours for 5 to 10 days.
  • Chronic bronchitis flare-ups for adults: The typical dose of Bactrim (sulfamethoxazole / trimethoprim) is 800 mg/160 mg (sulfamethoxazole/trimethoprim) taken by mouth every 12 hours for 14 days.
  • Pneumonia in people with compromised immune systems: The typical dose of Bactrim (sulfamethoxazole / trimethoprim) for both adults and children is based on your weight and is taken by mouth every 6 hours for 14 to 21 days.
  • Pneumonia prevention in people with compromised immune systems: The typical dose of Bactrim (sulfamethoxazole / trimethoprim) for adults is 800 mg/160 mg (sulfamethoxazole/trimethoprim) taken by mouth once daily. The dose given to children is based on their body size and is taken by mouth twice daily on 3 consecutive days per week. The maximum dose of Bactrim (sulfamethoxazole / trimethoprim) per day for children is 1600 mg/320 mg (sulfamethoxazole/trimethoprim).
  • Traveler's diarrhea in adults: The typical dose of Bactrim (sulfamethoxazole / trimethoprim) is 800 mg/160 mg (sulfamethoxazole/trimethoprim) taken by mouth every 12 hours for 5 days.

Frequently asked questions about Bactrim (sulfamethoxazole / trimethoprim)

Pros and cons of Bactrim (sulfamethoxazole / trimethoprim)


Thumbs UpAvailable as a pill, oral liquid, and injection

Thumbs UpAvailable as a cheap generic

Thumbs UpTreats many types of bacterial infections

Thumbs UpCan be given to children as young as 2 months old


Thumbs DownMakes your skin more sensitive to the sun

Thumbs DownCan upset your stomach or cause diarrhea

Thumbs DownShouldn't be given to people with severe liver or kidney problems

Thumbs DownNot safe for pregnant women

Thumbs DownIs a "sulfa" medication -- a common medication allergy

Pharmacist tips for Bactrim (sulfamethoxazole / trimethoprim)

Capsule IconFinish all of the Bactrim (sulfamethoxazole / trimethoprim) your healthcare provider prescribed for you, even if you start to feel better. Stopping Bactrim (sulfamethoxazole / trimethoprim) too soon can cause your infection to come back.

Capsule IconYou can take Bactrim (sulfamethoxazole / trimethoprim) with or without food, but some people experience nausea and vomiting after taking this medication. If these side effects happen to you, try taking Bactrim (sulfamethoxazole / trimethoprim) with food to help lessen them.

Capsule IconIf you have diarrhea after taking Bactrim (sulfamethoxazole / trimethoprim), try taking probiotic supplements to help lessen this side effect. Separate the probiotic from Bactrim (sulfamethoxazole / trimethoprim) by at least 1 hour to give Bactrim (sulfamethoxazole / trimethoprim) time to work before it kills the "good" bacteria from the probiotic. Be sure to continue the supplement for a few days after your last dose of Bactrim (sulfamethoxazole / trimethoprim).

Capsule IconBactrim (sulfamethoxazole / trimethoprim) makes your skin more sensitive to the sun, which means you may sunburn very easily. This is true even during the winter and on overcast days. Make sure to avoid sun exposure, wear a wide-brimmed hat, and use sunscreen with an SPF of at least 30 while you are taking Bactrim (sulfamethoxazole / trimethoprim).

Capsule IconTake Bactrim (sulfamethoxazole / trimethoprim) with 8 ounces of water and stay well hydrated while you are taking it. Bactrim (sulfamethoxazole / trimethoprim) goes through the kidneys and not drinking enough water can lead to kidney stones. Try to avoid too many beverages that cause dehyration, such as coffee and alcohol.

Capsule IconBactrim (sulfamethoxazole / trimethoprim) interacts with several medications, such as warfarin, phenytoin, methotrexate, and some diabetes medications. This is not a complete list of everything that interferes with Bactrim (sulfamethoxazole / trimethoprim). Be sure to tell your pharmacist about all medications you take, including things available over the counter, vitamins, and herbal supplements.

Capsule IconBactrim (sulfamethoxazole / trimethoprim) causes allergic reactions for a lot of people who take it. It belongs to a family of medications commonly called "sulfa drugs." If you experience any signs of an allergic reaction while taking Bactrim (sulfamethoxazole / trimethoprim), such as hives, rash, or swelling of the face, call your healthcare provider right away. Be sure to let all your providers and your pharmacist know if you develop an allergy to Bactrim (sulfamethoxazole / trimethoprim) so they can note it in your medical record.

Prices for Bactrim (sulfamethoxazole / trimethoprim) start at just $6.38 with a GoodRx coupon. They’re fast, easy-to-use and free!

View Coupon Prices

What are the side effects of Bactrim (sulfamethoxazole / trimethoprim)?

With any medication, there are risks and benefits. Even if the medication is working, you may experience some unwanted side effects.

Warning Small Contact your doctor immediately if you experience any of the following:

  • Allergic reactions
  • Severe skin reactions
  • Severe diarrhea
  • Low platelet count

Caution Small The following side effects may get better over time as your body gets used to the medication. Let your doctor know immediately if you continue to experience these symptoms or if they worsen over time.

Common side effects

  • Nausea
  • Vomiting
  • Loss of appetite
  • Rash
  • Hives

Other side effects

  • Severe diarrhea
  • Low blood sugar
  • Sensitivity to the sun

Source: FDA

The following side effects have also been reported:

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur:

More common

Black, tarry stools

blistering, peeling, or loosening of the skin

changes in skin color

chest pain or tightness


cough or hoarseness

dark urine




general feeling of tiredness or weakness


itching, skin rash

joint or muscle pain

light-colored stools

loss of appetite

lower back or side pain


pain, tenderness, or swelling of the foot or leg

painful or difficult urination

pale skin

red skin lesions, often with a purple center

red, irritated eyes

sore throat

sores, ulcers, or white spots in the mouth or on the lips

stomach pain

swollen or painful glands

trouble breathing

unpleasant breath odor

unusual bleeding or bruising

vomiting of blood

yellow eyes or skin

Incidence not known

Back, leg, or stomach pains

bleeding gums

blindness or vision changes


blood in the urine or stools

bluish-colored lips, fingernails, or palms

burning, crawling, itching, numbness, painful, prickling, "pins and needles", or tingling feelings

burning of the face or mouth

cloudy urine



continuing ringing or buzzing or other unexplained noise in the ears

cracks in the skin

decreased frequency or amount of urine

difficulty with swallowing

fainting spells

general body swelling

general feeling of discomfort or illness

hair loss

hearing loss


increased thirst


irregular heartbeat

large, flat, blue, or purplish patches in the skin

large, hive-like swelling on the face, eyelids, lips, tongue, throat, hands, legs, feet, or sex organs

loss of heat from the body

muscle or joint pain


not able to pass urine

numbness or tingling in the hands, feet, or lips

pain or burning while urinating

pinpoint red spots on the skin

puffiness or swelling of the eyelids or around the eyes, face, lips, or tongue

raised red swellings on the skin, the buttocks, legs, or ankles

redness of the white part of the eyes

redness, swelling, or soreness of the tongue


soreness of the muscles

stiff neck or back

stomach tenderness

swelling of the face, hands, legs, and feet

unsteadiness, trembling, or other problems with muscle control or coordination

weakness in the hands or feet

weakness or heaviness of the legs

weight gain or loss

Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

Passing of gas

Incidence not known


feeling of constant movement of self or surroundings

feeling sad or empty

increased sensitivity of the skin to sunlight

lack of feeling or emotion

loss of interest or pleasure


redness or other discoloration of the skin

seeing, hearing, or feeling things that are not there

sensation of spinning

severe sunburn

trouble concentrating

trouble sleeping


weight loss

Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.

Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

What are the risks and warnings for Bactrim (sulfamethoxazole / trimethoprim)?

Bactrim (sulfamethoxazole / trimethoprim) can cause some serious health issues. This risk may be even higher for certain groups. If this worries you, talk to your doctor or pharmacist about other options


Allergic reactions to Bactrim (sulfamethoxazole / trimethoprim) are possible, including life-threatening problems like anaphylaxis or airway swelling. Call 911 if this happens. If you notice hives, a rash, swelling of the lips or tongue, or difficulty breathing after taking Bactrim (sulfamethoxazole / trimethoprim), get medical help right away.


In some rare cases, people have developed really bad, potentially life-threatening skin reactions after starting Bactrim (sulfamethoxazole / trimethoprim). These are types of allergic rashes that are painful and create blisters all over the body. Get medical help right away if you notice a new rash, have a rash and a fever, unexplained blisters, or new sores inside your mouth.


Bactrim (sulfamethoxazole / trimethoprim) is known to harm unborn babies and can cause birth defects. If you become pregnant, stop taking Bactrim (sulfamethoxazole / trimethoprim) right away and talk to your healthcare provider. If you are taking Bactrim (sulfamethoxazole / trimethoprim) long term and would like to become pregnant, discuss other medication options with your healthcare provider before stopping Bactrim (sulfamethoxazole / trimethoprim).


Thrombocytopenia is a blood problem that sometimes happens in people taking Bactrim (sulfamethoxazole / trimethoprim). This side effect is rare, but it can be life-threatening. For most people, it will go away within a week of stopping Bactrim (sulfamethoxazole / trimethoprim). If you experience unusual fever, weakness, bruises or purple dots on the skin, or yellowing of the skin or eyes, get medical help right away.


It's important not to take Bactrim (sulfamethoxazole / trimethoprim) unless a healthcare provider tells you to do so. Bactrim (sulfamethoxazole / trimethoprim) doesn't treat all bacterial infections, including strep throat and scarlet fever. Taking Bactrim (sulfamethoxazole / trimethoprim) for an infection that it cannot treat can cause that infection to get worse. In some cases, this can lead to rheumatic fever, a painful condition that includes symptoms like a fever and inflamed joints.


  • Risk factors: Use of multiple antibiotics | Long-term use of antibiotics | People over 65 | Recent hospital stay | People with weakened immune systems | Previous infection from or known exposure to Clostridioides difficile

Like all antibiotics, Bactrim (sulfamethoxazole / trimethoprim) can cause diarrhea because it gets rid of the good bacteria in your gut. In rare cases, this diarrhea is caused by a bacteria called Clostridioides difficile (commonly called C. diff) that is usually kept under control by your gut bacteria. C. diff diarrhea is very contagious and can lead to life-threatening dehydration. If you have C. diff, be sure to wash your hands with soap for 20 seconds frequently and try to use a different bathroom from anyone living with you until you are better. Taking probiotic supplements while using Bactrim (sulfamethoxazole / trimethoprim) might help prevent this problem.


  • Risk factors: People with HIV being treated for pneumonia

Experts have found that people with HIV that are using Bactrim (sulfamethoxazole / trimethoprim) to treat pneumonia are more likely to die if they take Bactrim (sulfamethoxazole / trimethoprim) together with another medication called leucovorin. These two medications should not be taken together. If you take leucovorin on a regular basis, make sure your healthcare provider knows this before prescribing medication to treat your pneumonia.


  • Risk factors: Kidney problems | Liver problems | Nutrition problems | High doses of Bactrim (sulfamethoxazole / trimethoprim)

In some rare cases, people experience low blood sugar after taking Bactrim (sulfamethoxazole / trimethoprim) for a few days. This can happen to people with or without diabetes. Your risk of this is higher if you have kidney problems, liver problems, nutrition problems, or are on high doses of Bactrim (sulfamethoxazole / trimethoprim). Very low blood sugar can be life-threatening. Symptoms of low blood sugar include feeling shaky, being nervous or anxious, fast heartbeat, sweating or body chills, confusion, feeling sleepy, weakness or low energy, and being very hungry. Talk to your healthcare provider or pharmacist if you are concerned about this.

Interactions between Bactrim (sulfamethoxazole / trimethoprim) and other medications

Bactrim (sulfamethoxazole / trimethoprim) may interact with certain medications or supplements. Always let your doctor and pharmacist know about any other medications or supplements (including prescribed and over-the-counter medications, vitamins, and dietary or herbal supplements) that you are currently taking. The list below does not include all possible drug interactions with Bactrim (sulfamethoxazole / trimethoprim). Please note that only the generic name of each medication is listed below.

Using this medicine with any of the following medicines is not recommended. Your doctor may decide not to treat you with this medication or change some of the other medicines you take.

Using this medicine with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.

Using this medicine with any of the following medicines may cause an increased risk of certain side effects, but using both drugs may be the best treatment for you. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.

What are people’s reviews of Bactrim (sulfamethoxazole / trimethoprim)?

We asked 473 people what they think about Bactrim (sulfamethoxazole / trimethoprim):
Worth it

Drink lots of water and stay out of the sun.

Worth it

Just be mindful of if you are allergic to this medication, but it does the job effectively so I deal with the side effects.

Not worth it

UTI pain gone in 1 day but severe GI symptoms & fast heart rate started within 24 hrs of first dose.

Not sure

I was prescribed this for MRSA inside my nose. The side effects are very pronounced - nausea, lethargy, anxiety and more. Never had any from an antibiotic before. Very unpleasant. I'd pass on this if I could.

Worth it

I got relief from my UTI on the first day I took the medicine however I had some awful side effects.

How much does Bactrim (sulfamethoxazole / trimethoprim) cost?

Bactrim (sulfamethoxazole / trimethoprim) is available as a generic medication and may be significantly cheaper compared to the brand version. Unless there is a specific reason you need the brand, the generic medication will be a better value. For even more savings, use a GoodRx coupon and pay just a fraction of the retail price.

Lowest GoodRx Price
sulfamethoxazole / trimethoprim (generic)


View Prices & Coupons

Pricing based on most commonly-filled versions: 20 tablets of sulfamethoxazole / trimethoprim 800mg/160mg

What are alternatives to Bactrim (sulfamethoxazole / trimethoprim)?

There are a number of medications that your doctor can prescribe in place of Bactrim (sulfamethoxazole / trimethoprim). Compare a few possible alternatives below.

Bactrim (sulfamethoxazole / trimethoprim)
Drug Class:Sulfonamide Antibiotic


lowest GoodRx price

View Prices
Ciprofloxacin (Cipro)
Drug Class:Fluoroquinolone antibiotic


lowest GoodRx price

View Prices
Keflex (cephalexin)
Drug Class:Cephalosporin antibiotic


lowest GoodRx price

View Prices

What is the latest news about Bactrim (sulfamethoxazole / trimethoprim)?

Looking for Alternatives to Accutane? Here Are 5 Options
Looking for Alternatives to Accutane? Here Are 5 Options

What is Accutane and what are some alternatives to consider? Accutane is an effective medication for treating acne but can have concerning side effects. Luckily, there are alternatives to Accutane available. These treatments can help, but they also have side effects and other issues to be aware of.

5 Things You Can Do to Get Rid of a Urinary Tract Infection (UTI) Quickly
5 Things You Can Do to Get Rid of a Urinary Tract Infection (UTI) Quickly

Urinary tract infections (UTIs) are one of the most common infections in the United States. Close to half of all women and 12% of men will experience a UTI at least once in their lifetime. The symptoms are pretty distinct: pain or burning while urinating, increased urgency to urinate, cloudy or foul-smelling urine, and sometimes ...

What Are the Best Antibiotics to Help Treat a Urinary Tract Infection?
What Are the Best Antibiotics to Help Treat a Urinary Tract Infection?

Let’s be honest — a urinary tract infection probably isn’t your idea of a good time. Fortunately, we have several antibiotics that can treat a UTI. And while your healthcare provider will be the one writing your prescription, you may be curious about your options. So if you’re wondering what’s the best antibiotic for treating ...

What Are the Risks of Leaving a Urinary Tract Infection (UTI) Untreated?
What Are the Risks of Leaving a Urinary Tract Infection (UTI) Untreated?

If you’ve ever had a urinary tract infection, or UTI, you know that it’s usually treated with a prescription medication. But you may have wondered what happens if you choose not to treat it. Will a UTI go away on its own? Here, we discuss the risks of not treating a urinary tract infection, and ...

Can You Get Antibiotics for a Urinary Tract Infection (UTI) Without Seeing a Doctor?
Can You Get Antibiotics for a Urinary Tract Infection (UTI) Without Seeing a Doctor?

A urinary tract infection (UTI) is a common infection. It is usually caused by an overgrowth of bacteria in your urinary tract, your body’s system for making and draining urine. Most women and many men will have at least one UTI during their lifetime. Your likelihood of getting a UTI can be influenced by your ...

Get the latest news on medication savings tips and healthy living.

By signing up, I agree to GoodRx's terms and privacy policy, and to receive marketing messages from GoodRx.

Goodrx - Logo
GoodRx FacebookGoodRx InstagramGoodRx Twitter
Legitscript ApprovedPharmacyBBB Accredited Business