Generic name: sulfamethoxazole and trimethoprim [ SUL-fa-meth-OX-a-zole-and-trye-METH-oh-prim ]
Brand names: Bactrim, Bactrim DS
Dosage form: tablets (800 mg sulfamethoxazole and 160 mg trimethoprim, 400 mg sulfamethoxazole and 80 mg trimethoprim)
Drug class: Sulfonamides

Medically reviewed by Melisa Puckey, BPharm. Last updated on May 20, 2024.

What is Bactrim?

Bactrim and Bactrim DS are antibiotics used to treat ear infections, urinary tract infections, bronchitis, traveler's diarrhea, shigellosis, and Pneumocystis jiroveci pneumonia. Bactrim and Bactrim DS contain a combination of two antibiotics, sulfamethoxazole and trimethoprim, that treat different types of infection caused by bacteria. Bactrim DS (double strength) tablets are twice as strong as Bactrim tablets. 

Sulfamethoxazole is a sulfonamide antibiotic that prevents the growth of susceptible bacteria by interfering with their ability to make folic acid. Trimethoprim is an antifolate antibiotic that works by inhibiting an enzyme, resulting in bacteria's inability to make DNA and survive. Sulfamethoxazole and trimethoprim are combined because they are complementary and have a greater effect when used together. 

To help reduce the development of drug-resistant bacteria and maintain sulfamethoxazole-trimethoprim effectiveness, this medicine should be used only to treat infections proven or strongly suspected to be caused by susceptible bacteria.

Bactrim side effects

Common Bactrim side effects

Common Bactrim DS and Bactrim side effects are nausea, vomiting, loss of appetite, and skin rash.

Serious Bactrim and Bactrim DS side effects

Get emergency medical help if you have signs of an allergic reaction to this medicine (hives, cough, chest pain, shortness of breath, swelling in your face or throat) or a severe skin reaction (fever, sore throat, burning eyes, skin pain, red or purple skin rash with blistering and peeling).

Seek medical treatment if you have a serious drug reaction that can affect many parts of your body. Symptoms may include skin rash, fever, swollen glands, joint pain, muscle aches, severe weakness, pale skin, unusual bruising, or yellowing of your skin or eyes.

Call your doctor at once if you have:

• severe stomach pain, diarrhea that is watery or bloody (even if it occurs months after your last dose);
• any skin rash, no matter how mild;
• yellowing of your skin or eyes;
• a seizure;
• new or unusual joint pain;
• increased or decreased urination;
• swelling, bruising, or irritation around the IV needle;
• increased thirst, dry mouth, fruity breath odor;
• new or worsening cough, fever, trouble breathing;
• high blood potassium - nausea, weakness, tingly feeling, chest pain, irregular heartbeats, loss of movement;
• low blood sodium - headache, confusion, problems with thinking or memory, weakness, feeling unsteady; or
• low blood cell counts - fever, chills, mouth sores, skin sores, easy bruising, unusual bleeding, pale skin, cold hands and feet, feeling light-headed or short of breath.

Also, see the Warnings section.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

Related/similar drugs

prednisone, amoxicillin, doxycycline, ciprofloxacin, cephalexin, azithromycin, metronidazole

Warnings

You should not use this medicine if you have severe liver disease, kidney disease that is not being monitored, anemia caused by folic acid deficiency, if you take dofetilide, or if you have had low platelets caused by using trimethoprim or a sulfa drug.

You should not take this medicine if you are pregnant or breastfeeding.

Use this medicine only as directed. Tell your doctor if you use other medicines or have other medical conditions or allergies.

Before taking this medicine

You should not use this medicine  if you are allergic to sulfamethoxazole or trimethoprim, or if you have:

• severe liver disease;
• kidney disease that is not being treated or monitored;
• anemia (low red blood cells) caused by folic acid deficiency;
• a history of low blood platelets after taking trimethoprim or any sulfa drug; or
• if you take dofetilide.

Sulfamethoxazole and trimethoprim may cause birth defects. Do not use Bactrim if you are pregnant. Tell your doctor if you become pregnant.

Do not breastfeed.

This medicine should not be given to a child younger than 2 months old.

To make sure you can safely take this medicine, tell your doctor if you have ever had:

• kidney or liver disease;
• a folate (folic acid) deficiency;
• asthma or severe allergies;
• HIV or AIDS;
• a thyroid disorder;
• malnourishment;
• alcoholism;
• an electrolyte imbalance (such as low blood sodium or high potassium);
• porphyria, or glucose-6-phosphate dehydrogenase (G6PD) deficiency; or
• if you use a blood thinner (such as warfarin) and you have routine "INR" or prothrombin time tests.

How should I use Bactrim?

Take Bactrim exactly as prescribed by your doctor. Follow all directions on your prescription label and read all medication guides or instruction sheets.

Drink plenty of fluids to prevent kidney stones.

Antibiotic medicines can cause diarrhea. Tell your doctor if you have diarrhea that is watery or bloody.

Keep using this medicine even if your symptoms quickly improve. Skipping doses could make your infection resistant to medication. This antibiotic will not treat a viral infection (flu or a common cold).

You may need blood and urine tests, and this medicine may be stopped based on the results.

Store tablets at room temperature away from moisture, heat, and light. Do not refrigerate.

Bactrim Dosing Information

Bactrim is contraindicated in pediatric patients less than 2 months of age.

Bactrim tablets are available as

Bactrim DS (double strength) tablets: 800 mg sulfamethoxazole and 160 mg trimethoprim
Bactrim tablets: 400 mg sulfamethoxazole and 80 mg trimethoprim

Usual Bactrim dose for Urinary Tract Infections

Adults dose for UTI

Bactrim DS tablets (800mg/160mg): one tablet every 12 hours for 10 to 14 days
Bactrim tablets (400mg/80mg): two tablets every 12 hours for 10 to 14 days

Children (2 months and older) dose for UTI

Dose is based on weight: 40 mg/kg sulfamethoxazole and 8 mg/kg trimethoprim per 24 hours, given in two divided doses every 12 hours for 10 days.

Use: For the treatment of urinary tract infections due to susceptible strains of the following organisms: Escherichia coli, Klebsiellaspecies, Enterobacterspecies, Morganella morganii, Proteus mirabilis and Proteus vulgaris. It is recommended that initial episodes of uncomplicated urinary tract infections be treated with a single effective antibacterial agent rather than the combination.

Usual Bactrim dose Acute Otitis Media Children (2 months and older)

Dose is based on weight: 40 mg/kg sulfamethoxazole and 8 mg/kg trimethoprim per 24 hours, given in two divided doses every 12 hours for 10 days.
Use: For the treatment of acute otitis media in pediatric patients due to susceptible strains of Streptococcus pneumoniae or Haemophilus influenzae when sulfamethoxazole and trimethoprim offer some advantage over the use of other antimicrobial agents, in the judgment of the physician.

Usual Adult Bactrim Dose for Bronchitis

Bactrim DS tablets (800mg/160mg): one tablet every 12 hours 14 days
Bactrim tablets (400mg/80mg): two tablets every 12 hours 14 days
Use: For the treatment of acute exacerbations of chronic bronchitis due to susceptible strains of Streptococcus pneumoniae or Haemophilus influenzae when the physician deems that this drug could offer some advantage over the use of a single antimicrobial agent.

Usual Adult Bactrim Dose for Traveler's Diarrhea

Bactrim DS tablets  (800mg/160mg): one tablet every 12 hours 5 days
Bactrim tablets (400mg/80mg): two tablets every 12 hours for 5 days
Use: For the treatment of traveler's diarrhea due to susceptible strains of enterotoxigenic E coli.

For Patients with Impaired Renal Function

When renal function is impaired, a reduced dosage should be employed.

This is not all the dosing information available. For more detailed dosing information, click on the link below.

What happens if I miss a dose?

Use the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not use two doses at one time.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

Overdose symptoms may include loss of appetite, vomiting, fever, blood in your urine, yellowing of your skin or eyes, confusion, or loss of consciousness.

What should I avoid while using Bactrim?

This medicine could make you sunburn more easily. Avoid sunlight or tanning beds. Wear protective clothing and use sunscreen (SPF 30 or higher) when you are outdoors.

What other drugs will affect Bactrim?

You may need more frequent check-ups or medical tests if you also use medicine to treat depression, diabetes, seizures, or HIV.

Tell your doctor about all your current medicines. Many drugs can interact with sulfamethoxazole and trimethoprim, especially:

• amantadine, digoxin, cyclosporine, indomethacin, leucovorin, methotrexate, procainamide, pyrimethamine;
• an "ACE inhibitor" heart or blood presure medication (benazepril, enalapril, lisinopril, quinapril, ramipril, and others); or
• a diuretic or "water pill".

This list is not complete and many other drugs may interact with sulfamethoxazole and trimethoprim. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible drug interactions are listed here.

Storage

Store at 20° to 25°C (68° to 77°F).

Ingredients

Active ingredients: sulfamethoxazole and trimethoprim
Inactive ingredients: Docusate sodium, sodium benzoate, sodium starch glycolate type A potato , magnesium stearate and corn starch.

Company

Sun Pharmaceutical Industries, Inc. Cranbury, NJ 08512

Popular FAQ

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Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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