Bactrim – What it is, how it works and side effects!

Bactrim is indicated for the  treatment of infections caused by susceptible microorganisms. In addition, Bactrim can be combined with other medicines, as the combination of the medicines trimethoprim and sulfamethoxazole, such as certain respiratory, gastrointestinal, kidney and urinary tract infections, genitals (men and women), skin infections  , among other types of infections .

The medicinal action of Bactrim  Forte begins soon after the first intake, however, germs are not eliminated immediately. Therefore, even if some symptoms such as fever and pain disappear, it is necessary to continue taking Bactrim for as long as the doctor has established.

What is bactrim?

Bactrim  contains a combination of sulfamethoxazole and trimethoprim. Sulfamethoxazole and trimethoprim are both antibiotics that treat different types of infections  caused by bacteria. Bactrim  is used to treat ear infections , urinary  tract infections, bronchitis, traveler’s diarrhea , shigellosis and pneumonia.

Important Bactrim Information:

You should not use Bactrim  if you have severe liver or kidney disease, anemia caused by folic acid deficiency, or a history of low blood platelets caused by taking trimethoprim or any sulfa medication. Before taking this medicine you should not use Bactrim  if you are allergic to sulfamethoxazole or trimethoprim, or if you have:

  1. Severe liver or kidney disease;
  2. anemia  (low red blood cells) caused by folic acid deficiency;
  3. History of low blood platelets caused by using trimethoprim or any sulfa medication.

To Make Sure Bactrim is Safe for You, Tell Your Doctor If You Have:

  1. kidney or liver disease;
  2. folic acid deficiency;
  3. asthma or severe allergies;
  4. thyroid disorder ;
  5. HIV or AIDS;
  6. porphyria;
  7. G6 PD deficiency;
  8. malnutrition.

Do not use Bactrim  if you are pregnant. It can harm the fetus. Use effective birth control and tell your doctor if you become pregnant during treatment. Sulfamethoxazole and trimethoprim can pass into breast milk and harm a nursing baby. Tell your doctor if you are breastfeeding a baby. Do not give Bactrim  to a child under 2 months of age. Serious side effects may be more likely in older adults, especially those taking other medications, such as digoxin or certain diuretics.

How should I take bactrim?

  1. Take Bactrim  exactly as prescribed by your doctor. Follow all instructions on your prescription label;
  2. Do not take this medication in larger or smaller amounts or for longer than recommended;
  3. Shake Bactrim  well before putting in your dose;
  4. Measure the liquid with a spoon or medicine cup;
  5. If you do not have a dose measuring device, ask your pharmacist.

Use this medication for the entire prescribed period of time. Your symptoms may improve before the infection  is completely cleared. Skipping doses can also increase the risk of new antibiotic –  resistant infections . Bactrim  will not treat a viral infection  such as the common cold or flu.

  1. Drink plenty of fluids to prevent kidney stones while taking trimethoprim and sulfamethoxazole;
  2. This medication may cause unusual results with certain medical tests. Tell any doctor you are using Bactrim ;
  3. Store at room temperature away from moisture, heat and light.

What Happens if I Miss a Dose?

  1. Take the missed dose as soon as you remember;
  2. Skip the missed dose if it is almost time for your next scheduled dose;
  3. Do not take  extra Bactrim  to make up for a missed dose.

What Happens If You Overdose?

  • Seek emergency medical attention or call emergency services.

What should I avoid?

Antibiotics  can cause diarrhea , which can be a sign of a new infection . If you have watery or bloody diarrhea  , stop taking this medicine and call your doctor. Do not use anti-diarrheal medication unless your doctor recommends you do so. Avoid exposure to sunlight or tanning beds. This medicine can cause burns more easily. Wear protective clothing and sunscreen (factor 30 or higher) when outdoors.

Bactrim side effects:

Seek emergency medical help if you have any of these signs of an allergic reaction to Bactrim : hives; breathing difficulty; swelling of the face, lips, tongue or throat.

Call Your Doctor Immediately If You Have:

  1.  watery or bloody diarrhea ;
  2. Pale skin, feeling dizzy or short of breath, fast heart rate, or difficulty concentrating;
  3. sudden weakness or malaise, fever, chills, sore throat and cough;
  4. Cold or flu symptoms, swollen gums, painful mouth sores, pain when swallowing, skin sores;
  5. Low levels of sodium in the body – headache, confusion, slurred speech, severe weakness, vomiting, loss of coordination, feeling unsteady
  6. Liver problems – upper stomach pain, feeling tired, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes);
    or severe skin reaction – fever, sore throat , swelling of the face or tongue, burning eyes, skin pain, followed by a red or purple rash that spreads (especially on the face or upper body) and causes blisters and peeling.

Common Bactrim Side Effects Can Include:

  1. Nausea , vomiting, loss of appetite;
  2. Mild itching or rash.

What other medicines can interact with bactrim?

Tell your doctor about all the medicines you use and those you start or stop using during your treatment with Bactrim , especially:


This list is not complete. Other medications may interact with sulfamethoxazole and trimethoprim, including prescription and over-the-counter medications, vitamins, and herbal products. Not all possible interactions are listed in this medication guide.

Other information:

Remember to keep this and all other medicines out of the reach of children, never share your medicines with others and use Bactrim  only as prescribed. Always consult your physician to ensure that the information displayed on this page applies to your personal circumstances.

Bactrim side effects:

Along with necessary effects, trimethoprim/sulfamethoxazole may cause some undesirable effects. While not all of these side effects can occur, if they do, they may need medical attention. Check with your doctor right away if any of the following side effects occur while taking sulfamethoxazole/trimethoprim:

  1. Abdominal or stomach pain;
  2. black stools;
  3. Blisters, peeling or loosening of the skin;
  4. Changes in skin color;
  5. Chest pain;
  6. Goosebumps;
  7. Cough or hoarseness;
  8. dark urine;
  9. diarrhea ;
  10. Dizziness;
  11. Fever with or without chills;
  12. Feeling tired or weak;
  13. Headache;
  14. Itch;
  15. Joint or muscle pain;
  16. Light colored stools;
  17. loss of appetite;
  18. Low back pain;
  19. nausea ;
  20. Pain, tenderness or swelling of the foot or leg;
  21. Painful or difficult urination;
  22. Pale skin;
  23. Rash;
  24. Red skin lesions;
  25. Red and irritated eyes;
  26. Shortness of breathe;
  27. Sore throat ;
  28. Sores, ulcers or white patches in the mouth or lips;
  29. Swollen or painful glands;
  30. Chest tightness;
  31. Unpleasant odor;
  32. Unusual bleeding or bruising;
  33. Vomiting blood;
  34. Yellow eyes or skin;
  35. Dosage.


The adult dose for treating urinary  tract infections is 1 tablet of Bactrim  (double dose) or 2 tablets every 12 hours for 10 to 14 days. An identical daily dose is used for 5 days in the treatment of shigellosis.


The recommended dose for children with urinary  tract infections or acute otitis is 40 mg/kg sulfamethoxazole and 8 mg/kg trimethoprim for 24 hours, given in two divided doses every 12 hours for 10 days.

How Bactrim works:

Bactrim  is a brand name for a fixed combination medication containing two antibiotics – sulfamethoxazole and trimethoprim. Sulfamethoxazole prevents bacteria from producing dihydrophthalic acid and trimethoprim prevents the formation of tetrahydrofolic acid; both are significant in the formation of essential nucleic acids and proteins for many bacteria.

The sulfamethoxazole/trimethoprim combination is bactericidal (kills bacteria). Bactrim  belongs to the class of drugs known as antibiotics. The sulfamethoxazole component belongs to the class of drugs known as sulfonamides, and the trimethoprim component belongs to the class of drugs known as folic acid inhibitors.

Advantages of Bactrim:

Bactrim  is an antibiotic used to treat infections , such as those affecting the ear, urinary tract, lungs, or gastrointestinal tract. Active against a wide range of gram-positive and gram-negative bacteria, such as Streptococcus pneumoniae, Escherichia coli, Klebsiella species, Enterobacter species, and others.

Bacterial resistance is less likely to develop with Bactrim  than if either ingredient (sulfamethoxazole or trimethoprim) is given alone. Bactrim  is available as a generic under the name sulfamethoxazole/trimethoprim.

Disadvantages of Bactrim:

If you are between 18 and 60 years of age, do not take any other medication or have no other medical problems, the most likely side effects are: Nausea , vomiting, abdominal pain, diarrhea , inflammation of the mouth or tongue, weight loss , flatulence , rash and itchy skin.

It may not be suitable for some people, including people with kidney or liver disease, folate deficiency (elderly, chronic alcoholics, people taking anticonvulsants are at risk for folate deficiency), glucose-6-phosphate deficiency, porphyria, severe allergies, thyroid dysfunction, or bronchial asthma. Not suitable for pregnant or breastfeeding women or babies under two months of age.

  1. Elderly people may be more susceptible to Bactrim side effects ;
  2. May reduce blood sugar levels in people without diabetes ;
  3. It may interact with several other medications, including thiazides, warfarin, phenytoin, methotrexate, digoxin, and diabetes medications .
  4. interactions.

Drugs that may interact with Bactrim:

  1. Accutane (isotretinoína);
  2. Paracetamol;
  3. Albuterol;
  4. Amlodipine;
  5. Aspirin;
  6. Benadryl (Difenidramina);
  7. Ciprofloxacin;
  8. Coumadin (Warfarin);
  9. Diflucan (fluconazol);
  10. Doxycycline;
  11. Furosemide;
  12. Gabapentin;
  13. Ibuprofen;
  14. Keflex (cephalexin);
  15. Lasix (furosemida);
  16. Levothyroxine;
  17. Lisinopril;
  18. Meloxicam;
  19. Metformin;
  20. Methadone;
  21. Methotrexate;
  22. Metoprolol;
  23. Omeprazole;
  24. Prednisone;
  25. Rifampin;
  26. Tramadol;
  27. Trazodone;
  28. Tylenol (paracetamol);
  29. Vitamina B12 (cianocobalamina);
  30. Vitamina D3 (colecalciferol);
  31. warfarin;
  32. Wellbutrin (bupropion).

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