Antibiotics & You
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Sulfonamide combination

Co-trimoxazole (sulfamethoxazole with trimethoprim)

Prevention of infection in people with weakened immunity, such as after transplant or chemotherapySome urine and chest infections when other antibiotics are unsuitable
Start a diary for this antibiotic

Information follows NICE antimicrobial prescribing guidance and the BNF.

Common side effects

  • Feeling sick
  • Diarrhoea
  • Skin rash
  • Loss of appetite

How often each one happens varies by medicine and product, so check your leaflet. Many are mild, but ask your pharmacist or doctor if they are troublesome or do not settle.

Less common side effects

  • Sensitivity to sunlight
  • Headache
  • Sore mouth or tongue

Get medical help straight away if you notice

  • Blistering or peeling rash, or mouth or eye sores: stop the medicine and call 999 or go to A&E
  • Sore throat, fever, unusual bruising or bleeding (possible blood problem)
  • Yellowing of the skin or eyes

Taking it safely

  • Drink plenty of fluids.
  • You may need blood tests if you take it for a long time.
  • Tell your prescriber if you take methotrexate, warfarin or potassium medicines.

Report a side effect

You can report any suspected side effect to the UK Yellow Card scheme at yellowcard.mhra.gov.uk.