Medication Information Leaflet

What is this medication for?

Co-trimoxazole is an antibiotic made up of two different antibiotics (sulfamethoxazole and trimethoprim). Sulfamethoxazole belongs to a group of medicines known as sulphonamides and trimethoprim belongs to a group of medicines known as benzylpirimidines.

It is used to prevent and treat infections caused by certain bacteria, fungi and parasites. These may include infections of the lung, urinary tract, skin and soft tissue. Bactrim works by blocking two essential steps in the growth of bacteria.

How should I take/use this medication?

Co-Trimoxazole may be presented in a tablet, syrup or injectable form, of which will be chosen by your physician. This medication may be taken with or without food.

What should I do if I forget to take/use this medication?

If you forget to take a dose, take it as soon as you remember. However, if you remember the missed dose at the time you are due to take the next dose, omit the missed dose and only take the regularly scheduled dose. Do not take two doses to make up for the missed dose.

It is important to complete the course of antibiotic as prescribed by the doctor. Do not stop the antibiotic course midway, even if you feel better, unless you develop an allergic reaction to the antibiotic or experience severe side effects. In that case, see a doctor immediately.

What precautions should I take?

Inform your healthcare professional if:

  • You are allergic to sulfamethoxazole, trimethoprim, Co-trimoxazole or any of the other ingredients of co-trimoxazole tablet.

  • You are allergic to sulfa drugs (such as gliclazide or glibenclamide used for diabetes or thiazide diuretics used for high blood pressure) or have ever developed any rash, hives, swelling or shortness of breath after taking a sulfa drug.

  • You have a blood disorder that causes bruises or bleeding (thrombocytopenia), folate vitamin deficiency that causes you to feel tired, weak and breathless (anaemia) or a rare blood disorder called porphyria which can affect the skin or nervous system.

  • You have a certain other metabolic disorder known as glucose-6-phosphate dehydrogenase (G6PD) deficiency.

  • You have asthma, kidney or liver disease.

  • You are pregnant, planning to become pregnant, or breastfeeding. Discuss the risks and benefits with your doctor.

  • You are taking any other medications, including supplements, traditional medications and herbal remedies. These include:

    • Blood thinners such as warfarin

    • Methotrexate, a medicine used to treat certain cancers or certain diseases affecting the immune system

    • Phenytoin, a drug used to treat epilepsy (fits)

    • Drugs that can increase potassium levels such as ACE inhibitors (e.g. captopril, lisinopril), angiotensin receptor blockers (e.g. losartan) or aldosterone antagonists (e.g. spironolactone)

    • Medicines that are used to treat diabetes, such as glipizide or glibenclamide

    • Medicines used to treat problems with your heartbeats such as procainamide

    • Folinic acid

What are some common side-effects of this medication?

  • The most common side effects are gastrointestinal disturbances (nausea, vomiting, diarrhea, loss of appetite).

    • Take co-trimoxazole with a meal or a snack to reduce these side effects. If symptoms are severe or do not go away, consult your doctor.
  • This medication may make you more sensitive to the sun.

    • Avoid prolonged sun exposure. Use sunscreen and wear protective clothing when outdoors.
  • This medication may cause a fungal infection called thrush or candidiasis.

    • Contact your doctor if you experience vaginal itching/discharge or notice white spots in the lips/mouth.

What are some rare but serious side-effects that require immediate medical attention?

Stop taking co-trimoxazole and tell your doctor immediately if you have an allergic reaction. The symptoms of a drug allergy include one or more of the following:

  • Swollen face/eyes/lips/tongue

  • Difficulty in breathing

  • Skin rashes over your whole body

In rare instances, a skin rash may be followed by a more severe reaction, such as Stevens-Johnson Syndrome (SJS) and toxic epidermal necrolysis (TEN). These are life threatening skin-reactions, that are characterized by skin rash, multiple ulcers in the mouth/throat/nose/genitals, fever, and may progress to widespread blistering or peeling of the skin. Hence, do seek urgent advice from a healthcare provider immediately if any of the above occur.

Other rare side effects include:

  • Blood disorders – Signs of reduced:

    • Red blood cells - which can make the skin pale and cause weakness or breathlessness (anaemia) – Monitor for signs of extreme tiredness

    • Platelets (that help to stop bleeding) – Monitor for signs of abnormal bleeding or bruising

    • White blood cells (that help defend against infections) – Monitor for signs of infection such as prolonged fever or sore throat

  • Liver damage

    • Tender abdomen or loss of appetite, yellowing of the skin (jaundice), skin itch, light coloured stools or dark urine
  • Kidney problems

    • Monitor for swelling or puffiness in the face, abdomen, thighs or ankles or problems with urination
  • Changes in electrolyte levels in the blood – High levels of potassium (which can cause abnormal heart beats) or low levels of sodium

    • Blood tests to monitor these electrolytes are usually carried out by your physician
  • Severe intestinal condition (Clostridium difficile-associated diarrhoea) due to resistant bacteria. This may occur while receiving therapy or even weeks after treatment has stopped.

    • Inform your doctor immediately if you develop: persistent diarrhoea, stomach pain/cramping or blood/mucus in your stool

If you experience any of these symptoms, you should stop your medications and see your healthcare professional immediately.

How should I store this medication?

Keep this medicine away from heat and direct sunlight in a cool, dry place, out of reach of children

How should I throw away this medication safely?

Do return any unused/expired antibiotics to the pharmacy where you received them.


If you take more than the recommended dose, please seek medical advice immediately. The information provided on this page does not replace information from your healthcare professional. Please consult your healthcare professional for more information.

This article is jointly developed by members of the National Medication Information workgroup. The workgroup consists of cluster partners (National Healthcare Group, National University Health System and SingHealth), community pharmacies (Guardian, Unity and Watsons) and Pharmaceutical Society of Singapore. The content does not reflect drug availability and supply information in pharmacies and healthcare institutions. You are advised to check with the respective institutions for such information.

Last updated on Jul 2021

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