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Also known as trimethoprim-sulfamethoxazole, “Septra”, “Bactrim”, Apo-sulfatrim®, Novo-trimel®, Nu-cotrimox®

What is cotrimoxazole?

Cotrimoxazole contains two antibiotics:

  • trimethoprim
  • sulfamethoxazole.

It is used to prevent a type of infection called pneumocystis jirovecii pneumonia (PCP) in transplant patients. It also is also used to prevent urinary tract or bladder infections in kidney transplant patients.

You cannot take cotrimoxazole if you have an allergy to:

  • sulfonamides or “sulfa” drugs
  • trimethoprim.

You might not tolerate cotrimoxazole if you have glucose-6-phosphate dehydrogenase (G6PD) deficiency. Ask your transplant team for more information about this.

What cotrimoxazole looks like

Cotrimoxazole can come in a tablet or a liquid. Here is a photo of one brand of cotrimoxazole tablets used after a transplant.

Note: This photo is a close-up of the medication; it is not to scale.

Cotrimoxazole is available as:

  • 20 mg trimethoprim/100 mg sulfamethoxazole tablets
  • 80 mg trimethoprim/400 mg sulfamethoxazole tablets
  • 160 mg trimethoprim/800 mg sulfamethoxazole “DS” tablets
  • 8 mg trimethoprim/40 mg sulfamethoxazole/mL suspension (liquid).

How to take cotrimoxazole

  • Wash your hands before and after handling cotrimoxazole.
  • If you have a kidney transplant, take cotrimoxazole at the same time(s) every day.
  • If you have a heart, liver, lung or small bowel transplant, take cotrimoxazole at the same time of day three times a week.
  • Take cotrimoxazole with a full glass of water, juice or milk – it is important to drink plenty of fluid with this medicine.
  • You can take cotrimoxazole with food or without food, but make sure you take it the same way each time.

What to do if you miss a dose of cotrimoxazole

  • Take the missed dose as soon as you remember.
  • If it is almost time for the next dose, skip the missed dose. Take the next dose at the regular time.
  • Never take two doses to make up for the missed dose.
  • Call your transplant team if you have missed more than one dose or if you have trouble remembering to take cotrimoxazole.

What to do if you vomit a dose of cotrimoxazole

When you take a dose of medicine, it usually takes an hour to pass from your stomach into your blood. The transplant pharmacist will talk with you about this after your transplant.

  • If you throw up more than one hour after taking cotrimoxazole: there is no need to repeat the dose.
  • If you throw up less than one hour after taking cotrimoxazole and you are using it to prevent (not treat) infection, it is ok to miss that dose. If you are sick enough that you throw up another dose at a different time on the same day, talk to your transplant team to check if you need to repeat a dose. We will decide based on what is going on with you at that time (for example what type of infection you may have or if you have a low blood cell count).
  • If you repeat a cotrimoxazole dose, and you throw it up too, do not repeat it again.

Keep track of any vomited or repeated cotrimoxazole doses and talk to your transplant team or family doctor if you are vomiting a lot. Use this chart to help you decide when to call for advice.

You may not feel like eating or drinking when you are vomiting (even if does not happen around your medication times). But you risk becoming dehydrated if you do not drink.

What to do if you have diarrhea (watery stools)

Diarrhea (watery stools) can reduce the amount of cotrimoxazole that passes from your stomach into your blood. This could result in too little cotrimoxazole in your blood. Frequent diarrhea can also cause you to become dehydrated. This chart will help you decide if you need to contact your transplant team or family doctor for help with managing diarrhea.

Possible side effects of cotrimoxazole

  • Nausea (upset stomach), vomiting (throwing up)
  • Diarrhea (watery stools)
  • Mild headache
  • Rash
  • Skin sensitivity to the sun
  • Tiredness or fatigue – cotrimoxazole can lower your hemoglobin, or red blood cell, count (hemoglobin provides energy to the body)
  • Heavier or longer bleeding from any cuts – cotrimoxazole can lower your platelet count (platelets help stop bleeding)
  • Greater risk of infections – cotrimoxazole lowers your white blood cell count (white blood cells help fight infection), something that is more common than any changes to your red blood cells or platelets
  • Stevens-Johnson syndrome, a rare side effect that involves a type of skin blistering on different tissues in the body

Taking cotrimoxazole with other medicines

Some medicines may change the way cotrimoxazole works in your body. Always call your transplant team before using any new medicines, whether:

  • your doctor prescribes them
  • you buy them "over-the-counter" at a drugstore
  • they are herbal or natural medicines.

How to store cotrimoxazole

  • Keep cotrimoxazole out of reach of any small children.
  • Keep it at room temperature.
  • Store it in a cool, dry place away from sunlight.
  • Never store it in the bathroom or near heat sources in the kitchen.
  • Never store it in the refrigerator or freezer.

Taking cotrimoxazole safely

If you develop a rash, stop taking cotrimoxazole and call the transplant team for advice.

It is important to protect your skin from sun damage when your immune system is weak. Damage to the skin can develop into skin cancer later in life. Cotrimoxazole makes your skin more sensitive to the sun. This means that you will burn more easily!

How the transplant team checks how well cotrimoxazole is working

The transplant team checks for signs of infection. They will also ask you to report any signs or symptoms of infection (for example fever, cough, a burning feeling when you urinate (pee) or shortness of breath).

Other important tips

  • Keep a list of all of your medications in your wallet or purse so you can show it to doctors, nurses and pharmacists when needed.
  • Make sure that your family doctor and dentist know that you are taking cotrimoxazole before you have any treatments.
  • If you are sexually active, be aware that cotrimoxazole could cause birth defects if it is taken at the time of conception or during pregnancy. Always use a condom, not only to prevent pregnancy but also to prevent sexually transmitted infections.

If there comes a time when you want to have a child, you can talk to your transplant team. Changes to your medications may be possible to ensure a safe pregnancy for you and your partner.

What to do if someone else takes your cotrimoxazole

Call your local poison information centre.

If you live in Ontario, call the Ontario Poison Centre. The calls are free.

  • Call 416-813-5900 if you live in Toronto.
  • Call 1-800-268-9017 if you live elsewhere in Ontario.
Last updated: August 6th 2023