Bactrim General Information

Bactrim (Sulfamethoxazole/Trimethoprim) is an antibiotic combination used to treat or prevent infections. Bactrim is a synthetic antibacterial combination product available in DS (double strength) tablets.

How to use

Use Bactrim as directed by your doctor.

  • Take Bactrim by mouth with or without food.
  • Bactrim works best if it is taken at the same time each day.
  • Take Bactrim with a full glass of water (8 oz/240 mL). Drink several extra glasses of water a day unless otherwise directed by your doctor.
  • To clear up your infection completely, take Bactrim for the full course of treatment. Keep taking it even if you feel better in a few days.

Ask your health care provider any questions you may have about how to use Bactrim.

Drug Class and Mechanism

Bactrim is an antibiotic combination containing a sulfonamide antibiotic. It works by killing sensitive bacteria.

This drug contains two active substances—sulfamethoxazole and trimethoprim, which have a joint action by blocking two enzymes that catalyze the successive stages of the biosynthesis of folinic acid in microorganisms. This mechanism provides a bactericidal effect when achieved at this concentration, in which the individual components of the drug have only bacteriostatic effects. In addition, Bactrim is often effective against pathogens that are resistant to one of its components.


Bactrim is used to treat infections of the upper and lower respiratory tracts and upper respiratory tract, acute and chronic bronchitis, bronchiectasis, pneumonia (including those caused by Pneumocystis carinii), pharyngitis, tonsillitis (with infections caused by b-hemolytic group A streptococcus, eradication rate is low), sinusitis, otitis media.
Infections of the kidney and urinary tract include acute and chronic cystitis, pyelonephritis, urethritis, prostatitis, and chancroid.

Infections of the digestive tract, including typhoid and paratyphoid, shigellosis (caused by susceptible strains of Shigella flexneri and Shigella sonnei), diarrhea in travelers due to enterotoksicheskimi strains of Escherichia coli, and cholera (in conjunction with rehydration therapy). Infections of skin and soft tissue include pyoderma, furunculosis, abscesses, and infected wounds. Other bacterial infections include: acute and chronic osteomyelitis, acute brucellosis; nocardiosis, actinomycosis, toxoplasmosis, South American blastomycosis.

Missed Dose

If you miss a dose of Bactrim, take it as soon as possible. If it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not take 2 doses at once.


Store Bactrim at 77 degrees F (25 degrees C). Store it away from heat, moisture, and light. Do not store it in the bathroom. Keep Bactrim out of the reach of children and away from pets.


Do not use Bactrim if:

  • you are allergic to any ingredient in Bactrim or to similar medicines;
  • you had a severe allergic reaction to any other sulfonamide (sulfa) medicine (eg, glipizide, hydrochlorothiazide);
  • you are taking dofetilide;
  • you have anemia caused by low levels of folate in the blood or urinary blockage;
  • you are in week 38 of pregnancy or later (full-term) or you are breast-feeding;
  • the patient is a child younger than 2 months old.

Contact your doctor or health care provider right away if any of these apply to you.


  • Bactrim may cause you to become sunburned more easily. Avoid the sun, sunlamps, or tanning booths until you know how you react to Bactrim. Use a sunscreen or wear protective clothing if you must be outside for more than a short time.
  • Contact your doctor right away if stomach pain or cramps, severe diarrhea, or bloody stools occur. Do not treat diarrhea without first checking with your doctor.
  • Be sure to use Bactrim for the full course of treatment. If you do not, the medicine may not clear up your infection completely. The bacteria could also become less sensitive to this or other medicines. This could make the infection harder to treat in the future.
  • Bactrim only works against bacteria; it does not treat viral infections (e.g., the common cold).
  • Long-term or repeated use of Bactrim may cause a second infection. Tell your doctor if signs of a second infection occur. Your medicine may need to be changed to treat this.
  • Diabetes patients – Bactrim may affect your blood sugar. Check blood sugar levels closely. Ask your doctor before you change the dose of your diabetes medicine.
  • Use Bactrim with extreme caution in children younger than 10 years old who have diarrhea or an infection of the stomach or bowel.
  • Bactrim may interfere with certain lab tests. Be sure your doctor and lab personnel know you are taking Bactrim.
  • Lab tests, including complete blood cell counts and kidney function tests, may be performed while you use Bactrim . These tests may be used to monitor your condition or check for side effects. Be sure to keep all doctor and lab appointments.
  • Pregnancy and breast-feeding: If you become pregnant, contact your doctor. You will need to discuss the benefits and risks of using Bactrim while you are pregnant. Do not use Bactrim if you are in week 38 of pregnancy or later (full-term). Bactrim is found in breast milk. Do not breast-feed while taking Bactrim.

Common Side Effects

Check with your doctor if any of these most common side effects persist or become bothersome:

  • appetite loss; nausea; vomiting.

Severe Side Effects

Seek medical attention right away if any of these severe side effects occur:

  • severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue);
  • blistered, peeling, red, or swollen skin;
  • bloody or black, tarry stools;
  • chest pain;
  • chills, fever, or sore throat;
  • decreased urination;
  • depression;
  • hallucinations;
  • irregular heartbeat;
  • joint or muscle pain;
  • painful or stiff neck;
  • purple patches under the skin;
  • seizures;
  • severe diarrhea;
  • severe or persistent cough;
  • severe or persistent headache;
  • severe or persistent nausea or vomiting;
  • shortness of breath;
  • stomach cramps/pain;
  • unusual bruising or bleeding;
  • unusual tiredness or weakness;
  • unusually pale skin;
  • vaginal irritation or discharge;
  • yellowing of the skin or eyes.