Co-trimoxazole (Septrin®)

Co-trimoxazole is an antibiotic 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 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.

How is co-trimoxazole given?

Co-trimoxazole is given by mouth in tabletor 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) through a cannula, central venous catheter or implantable port to treat PCP.

What are the side effects of co-trimoxazole?

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 not controlled or persists.

Bone marrow suppression

Some children are sensitive to cotrimoxazole and this can show itself by a reduction in how well your child’s bone marrow works. This means he or she may become anaemic, 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 thioguanine 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 an 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.


Please tell the doctor or nurse if your child has diarrhoea which is not controlled or persists. It is important that your child drinks lots of fluids.

Sensitivity to sunlight

While your child is having co-trimoxazole, their skin may be more sensitive to sunlight. If your child does go out in the sun, always use a good sunblock of SPF25 or higher and ensure they wear a sunhat.

Co-trimoxazole and 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.

Important information you should know about co-trimoxazole:

  • Keep the tablets or liquid in a safe place where children cannot reach them.
  • Tablets and liquids should be kept in a cool, dry place away from direct sunlight or heat.
  • 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, he or she will need to be treated with other drugs to prevent PCP.
  • 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 tablets to the pharmacist. Do not flush them down the toilet or throw them away.
Compiled by: 
The Pharmacy department in collaboration with the Child and Family Information Group
Last review date: 
April 2013


Please read this information sheet from GOSH alongside the patient information leaflet (PIL) provided by the manufacturer. If you do not have a copy of the manufacturer’s patient information leaflet please talk to your pharmacist. A few products do not have a marketing authorisation (licence) as a medicine and therefore there is no PIL.

For children in particular, there may be conflicts of information between the manufacturer’s patient information leaflet (PIL) and guidance provided by GOSH and other healthcare providers. For example, some manufacturers may recommend, in the patient information leaflet, that a medicine is not given to children aged under 12 years. In most cases, this is because the manufacturer will recruit adults to clinical trials in the first instance and therefore the initial marketing authorisation (licence) only covers adults and older children.  

For new medicines, the manufacturer then has to recruit children and newborns into trials (unless the medicine is not going to be used in children and newborns) and subsequently amend the PIL with the approved information. Older medicines may have been used effectively for many years in children without problems but the manufacturer has not been required to collect data and amend the licence. This does not mean that it is unsafe for children and young people to be prescribed such a medicine ‘off-licence/off-label’. However, if you are concerned about any conflicts of information, please discuss with your doctor, nurse or pharmacist.