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Cotrim

Generic name: sulfamethoxazole and trimethoprim

Brand names: Bactrim, Cotrim (discontinued), Septra, Sulfatrim Pediatric

Last updated October 2, 2026 0 views Reviewed by Philip Thornton, DipPharm
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What is Cotrim?

Cotrim is an antibiotic combination containing sulfamethoxazole and trimethoprim, and it works by killing sensitive bacteria. Both ingredients are antibiotics that treat different types of infection caused by bacteria.

Cotrim is used to treat ear infections, urinary tract infections, bronchitis, traveler's diarrhea, and Pneumocystis carinii pneumonia. The Cotrim brand has been discontinued, but generic sulfamethoxazole and trimethoprim formulations are still available.

Cotrim may also be used for other purposes not listed in this medication guide.

How should I take Cotrim?

Take Cotrim exactly as prescribed by your doctor. Do not take it in larger amounts or for longer than recommended. Follow the directions on your prescription label.

Take Cotrim for the full prescribed length of time. Your symptoms may improve before the infection is completely cleared. Cotrim will not treat a viral infection such as the common cold or flu. Drink plenty of fluids to prevent kidney stones while you are taking trimethoprim and sulfamethoxazole. Store the tablets and liquid at room temperature away from moisture, heat, and light.

Warnings

You should not use Cotrim if you are allergic to sulfamethoxazole or trimethoprim, or if you have anemia (lack of red blood cells) caused by folic acid deficiency, a history of low blood platelets caused by taking trimethoprim or a sulfa drug, severe liver disease, or severe kidney disease that cannot be monitored. Do not use Cotrim if you take dofetilide.

Before using Cotrim, tell your doctor if you have kidney or liver disease, a folic acid deficiency, asthma or severe allergies, AIDS, a glucose-6-phosphate dehydrogenase deficiency (G6PD deficiency), or if you are malnourished.

Take Cotrim for the full prescribed length of time. Your symptoms may improve before the infection is completely cleared. Cotrim will not treat a viral infection such as the common cold or flu.

Antibiotic medicines can cause diarrhea, which may be a sign of a new infection. If you have diarrhea that is watery or has blood in it, call your doctor. Do not use any medicine to stop the diarrhea unless your doctor has told you to.

Avoid exposure to sunlight, sunlamps, or tanning beds. Cotrim can make your skin more sensitive to sunlight, and a sunburn may result. Wear protective clothing and use sunscreen (SPF 15 or higher) when you are outdoors.

Before taking this medicine

You should not use Cotrim if you are allergic to sulfamethoxazole or trimethoprim, or if you have anemia (lack of red blood cells) caused by folic acid deficiency, a history of low blood platelets caused by taking trimethoprim or a sulfa drug, severe liver disease, or severe kidney disease that cannot be monitored. Do not use Cotrim if you take dofetilide.

If you have certain conditions, you may need a dose adjustment or special tests to safely use this medication. Before using Cotrim, tell your doctor if you have:

  • kidney or liver disease;
  • a folic acid deficiency;
  • asthma or severe allergies;
  • AIDS;
  • a glucose-6-phosphate dehydrogenase deficiency (G6PD deficiency); or
  • if you are malnourished.

Tell your doctor if you are pregnant. This medicine could harm the unborn baby or cause birth defects.

Tell your doctor if you are breast-feeding a baby. Sulfamethoxazole and trimethoprim can pass into breast milk and may harm a nursing baby.

Do not give Cotrim to a child younger than 2 months old. Older adults may be more likely to have side effects while taking this medication.

Cotrim side effects

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

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, muscle aches, severe weakness, unusual bruising, or yellowing of your skin or eyes.

Call your doctor at once if you have a serious side effect such as:

  • severe stomach pain, diarrhea that is watery or bloody (even if it occurs months after your last dose);
  • new or worsening cough, shortness of breath, or chest pain;
  • a 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;
  • an electrolyte imbalance - headache, confusion, weakness, slurred speech, tingly feeling, chest pain, irregular heartbeats, loss of coordination or movement, feeling unsteady, vomiting; 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.

Common side effects may include:

  • nausea, vomiting, loss of appetite; or
  • skin rash.

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 FDA at 1-800-FDA-1088.

What happens if I miss a dose?

Take the missed dose as soon as you remember. If it is almost time for your next dose, wait until then to take the medicine and skip the missed dose. Do not take extra medicine to make up the missed dose.

What happens if I overdose?

Seek emergency medical attention if you think you have used too much of this medicine.

Overdose can cause dizziness, drowsiness, nausea, vomiting, loss of appetite, stomach pain, headache, yellowing of your skin or eyes, blood in your urine, fever, confusion, or fainting.

Antibiotic medicines can cause diarrhea, which may be a sign of a new infection. If you have diarrhea that is watery or has blood in it, call your doctor. Do not use any medicine to stop the diarrhea unless your doctor has told you to.

Avoid exposure to sunlight, sunlamps, or tanning beds. Cotrim can make your skin more sensitive to sunlight, and a sunburn may result. Wear protective clothing and use sunscreen (SPF 15 or higher) when you are outdoors.

What other drugs will affect Cotrim?

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 affect sulfamethoxazole and trimethoprim, especially:

  • amantadine, cyclosporine, indomethacin, leucovorin, methotrexate, pyrimethamine, dofetilide, warfarin, phenytoin, digoxin, tricyclic antidepressants, oral diabetes medicines, zidovudine, or procainamide;
  • an "ACE inhibitor" heart or blood presure medication (benazepril, enalapril, lisinopril, quinapril, ramipril, and others); or
  • a diuretic or "water pill" (chlorthalidone, hydrochlorothiazide, and others).

This list is not complete and there may be other drugs that can interact with Cotrim. Tell your doctor about all your prescription and over-the-counter medications, vitamins, minerals, herbal products, and drugs prescribed by other doctors. Do not start a new medication without telling your doctor.

Common questions about Cotrim

What happens if antibiotics don’t work for UTI?
If an antibiotic does not fully treat your UTI, the bacteria may be resistant and the infection can get worse. You may need more testing or a different antibiotic. A bladder infection can spread to the kidneys or bloodstream, causing a serious medical emergency. Contact your healthcare provider if your symptoms do not improve. Continue reading
What drugs should be avoided with a sulfa allergy?
People with a sulfa allergy typically need to avoid sulfonamide antibiotics (antibiotics containing sulfa), including: Septra and Bactrim (sulfamethoxazole-trimethoprim) Pediazole (erythromycin-sulfisoxazole) Whether other nonantibiotic sulfa-containing drugs need to be avoided with sulfa allergy is unclear and considered on a case-by-case basis. Continue reading
Does Bactrim cause headaches?
Yes. Headache is a common side effect of Bactrim (sulfamethoxazole / trimethoprim) and may occur in up to 10% of patients. Most Bactrim headaches are mild and fade once treatment ends. In rare cases, a headache can be a warning sign of a serious side effect, such as aseptic meningitis, low blood sugar, or low sodium in the blood. Continue reading

Related medicines

Before you take this medicine: the information on this page is general and may not cover your personal circumstances. Read the label supplied with your medicine and ask a pharmacist or doctor if you are unsure, especially if you are pregnant, breastfeeding, taking other medicines or managing a long-term condition.
General medicine information Consumer-friendly language Source: Drugs.com

Content is provided for education and is not medical advice. See our medical disclaimer. Source page medically reviewed by Philip Thornton, DipPharm on October 2, 2026.