This popular antibiotic is a combination of two sulfa drugs, sulfamethoxazole and trimethoprim.

It is frequently prescribed for urinary tract infections, middle ear infections, chronic bronchitis, diarrhea caused by Shigella, and pneumonia due to Pneumocystis carinii.

It is occasionally prescribed for travelers’ diarrhea.

Co-trimoxazole is available in single- and double-strength tablets and suspensions for pediatric use.

Side Effects and Interactions

Side effects from co-trimoxazole may include nausea, vomiting, diarrhea, stomach ache, hives, peeling of skin, itching, headache, insomnia, weakness, dizziness, and depression.

Blood disorders and liver damage are unusual but potentially serious. If a rash appears, contact the doctor without delay. Severe skin reactions, while rare, begin with a rash.

Co-trimoxazole can make skin and eyes more sensitive to the sun. It is wise to prevent problems by using sunscreen, protective clothing, a hat, and effective sunglasses.

Remember to report any symptoms or suspected side effects to your physician. Notify the doctor immediately if you develop sore throat, fever, chills, yellowing of skin or eyes, and unusual bleeding or bruising.

Co-trimoxazole may interact with Coumadin, diabetes pills such as Diabinese, Orinase or Tolinase, hydrochlorothiazide or certain other diuretics, Dymelor, methotrexate, cyclosporine, and Dilantin.

Be sure to check with your physician and pharmacist before taking co-trimoxazole together with any other drugs.

Special Precautions

If you are allergic to sulfa drugs, alert your physician immediately.

People who have reacted to other sulfa drugs, including diabetes pills and thiazide blood pressure medicines, should not take co-trimoxazole.

Symptoms such as breathing difficulty, wheezing, sneezing, hives, itching, and skin rash require immediate emergency treatment.

Life-threatening anaphylactic shock may produce an inability to breathe and cardiovascular collapse and can occur within minutes of exposure.

Co-trimoxazole is not prescribed for women at or after 36 weeks of pregnancy, for breastfeeding mothers, or babies less than two months old.

Elderly people may need lower doses, especially if kidneys or liver are not functioning well.

Prolonged use of an antibiotic like co-trimoxazole sometimes leads to an overgrowth of fungus or resistant bacteria known as superinfection. If this occurs, the doctor may need to have you discontinue this drug and take a different medication.

Taking the Medicine

Co-trimoxazole is best swallowed on an empty stomach, at least one hour before or two hours after a meal, with a full glass of water.

If it causes stomach upset, it may be taken at mealtime.

Be sure to finish the entire prescription unless your doctor directs you to stop.

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  1. Karen

    I was prescribed this after a kidney transplant. Two days after starting it, I developed a rash around my stomach. The rash has grown and continues to spread. Two consultants and a GP have no idea what would cause this rash so I decided to investigate the side effects of all the drugs I take and this one seems to be the culprit. I have been referred to a dermatologist.

  2. Dave

    This is another antibiotic I received today (Sulfamethoxazole), for infection/bacteria. I had a large boil removed from under my right armpit. I am to take 2 tablets 2 times a day and will probably take them in the morning before departing for work and in the evening before retiring. My biggest concern is side-effects since this is my first time taking them.
    I thoroughly enjoy reading all your comments. I learn a lot from other patients who are taking the same medications.

  3. Mrs Wilson

    I took a dosage of 50/10 sulfamethoxazole/trimethoprim every 6 hours for 20 days. It cleared up my ears, glands, cough, sinus congestion, gums, and joint discomfort, with no yeast infection. Vitamins, minerals, (high antioxidants) and water are helping to maintain the wonderful benefits of this treatment. I am a smoker, coffee drinker, and all food group balanced meal consumer, weighing 125lbs, height of 5’4″, and 49 yrs old.

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