Co-trimoxazole (Septrin®)

This is an antibiotic. It is used to prevent and treat a type of chest infection called Pneumocystis Jiroveci pneumonia. You may hear the doctors and nurses referring to this as ‘PCP’ as it was previously called Pneumocystis Carinii pneumonia. This page explains what co-trimoxazole is, how it is given and some of the possible side effects. Each person reacts differently to medicines, so your child will not necessarily suffer from every side effect mentioned. If you have any questions or concerns, please speak to your doctor, nurse or pharmacist.Pneumocystis Jiroveci pneumonia infection is due to an organism (bug) that is probably present in most people’s lungs. Children who are receiving long term medicines which interfere with the body’s ability to cope with infections may be more at risk from this type of pneumonia. The symptoms of this infection are a raised temperature, rapid breathing and a dry cough.

Co-trimoxazole is given by mouth in tablet or liquid form. When co-trimoxazole is given by mouth, it is usually given to prevent PCP.

It can be given in higher doses into a vein (intravenously or IV) through a cannula, central venous catheter or implantable port to treat PCP.

What are the side effects?

Nausea and vomiting

Anti-sickness drugs can be given to reduce or prevent these symptoms. Please tell your doctor or nurse if your child’s sickness is very bad or continues for more than a few days.

Bone marrow suppression

Some children are sensitive to co-trimoxazole and this can show itself by a reduction in how well your child’s bone marrow works. This means they may become anaemic (reduced red blood cells), bruise or bleed more easily than usual, and have a higher risk of infection.

Please tell your doctor if your child seems unusually tired, has bruising or bleeding, or any signs of infection, especially a high temperature.

Children who are sensitive to co-trimoxazole may find that their bone marrow is more likely to be supressed when taking mercaptopurine or allopurinol as well as co-trimoxazole. Your child’s blood count will be checked regularly and individual advice will be given by your doctor.

Allergic reaction

Some children receiving co-trimoxazole have an allergic reaction to the drug. This reaction may be mild to severe.

Signs of a mild allergic reaction include skin rashes and itching, high temperature, shivering, redness of the face, a feeling of dizziness or headache. If you see any of these signs, please report them to a doctor or nurse.

Signs of a severe allergic reaction include any of the above, as well as difficulty in breathing or chest pain. If you are in hospital and your child shows signs of a severe allergic reaction, call a doctor or nurse immediately. If you are at home and your child shows signs of a severe allergic reaction, call an ambulance immediately.

Diarrhoea or stomach pain

Please tell the doctor or nurse if your child has diarrhoea or stomach pain which is very bad or continues for more than a few days. It is important that your child drinks lots of fluids.

Sensitivity to sunlight

While your child is taking this medicine, they should use an effective sunscreen (SPF 50 or above) and wear a hat whenever outdoors.

Interactions with other medicines

Some medicines can react with co-trimoxazole, altering how well it works. Always check with your doctor or pharmacist before giving your child any other medicine, including medicines on prescription from your family doctor (GP), medicines bought from a pharmacy (chemist) or any herbal or complementary medicines.


  • Keep all medicines in a safe place where children cannot reach them.
  • Co-trimoxazole may need to be stopped before some courses of treatment. Please discuss with your doctor, nurse or pharmacist. If the co-trimoxazole has to be stopped, it is very important to clearly mark this in your child’s shared care book and to tell the doctor or nurse if your child becomes unwell. In some instances, they will need to be treated with other medicines to prevent PCP instead.
  • If your child vomits straight after taking the dose, inform your local doctor or nurse, as your child may need to take another one. Do not give them another dose without informing the doctor or nurse.
  • If you forget to give your child a dose, do not give a double dose. Inform your doctor or nurse and keep to your child’s regular schedule
  • If your doctor decides to stop treatment with co-trimoxazole or the medicine passes its expiry date, return any remaining medicine to the pharmacist. Do not flush it down the toilet or throw it away.
Compiled by:
The Pharmacy department in collaboration with the Child and Family Information Group
Last review date:
September 2019