Sounds like 'co-tri-mox-a-zole'

Co-trimoxazole is an antibiotic used to treat different infections caused by bacteria. Find out how to take it safely and possible side effects. Co-trimoxazole is also called Trisul or Deprim.

Type of medicine Also called
  • Combination antibiotic (to treat infections)
  • Sulphur antibiotic (sulfamethoxazole) and trimethoprim
  • Trisul (tablet)
  • Deprim (liquid)

What is co-trimoxazole?

Co-trimoxazole is an antibiotic that is used to treat bacterial infections such as bladder infections, skin infections or chest infections. It works by killing or stopping the growth of bugs that cause infection. It is not effective against infections caused by viruses. 

Co-trimoxazole is made up of two antibiotics (trimethoprim  and sulfamethoxazole). Sulfamethoxazole belongs to a group of antibiotics called sulphonamides. In New Zealand co-trimoxazole is available as tablets and liquid and can also be given as an injection in the hospital. 


  • The dose of co-trimoxazole will be different for different people depending on the type of infection and your age.
  • Adults – the usual dose for adults is 2 tablets twice a day.
  • Children – the dose for children will depend on their body weight. It is usually given 2 times a day.
  • Your doctor will advise you how long to take co-trimoxazole for (usually 5 to 7 days) but for urinary tract infections, it may only be needed for 1 to 3 days.
  • Always take your co-trimoxazole exactly as your doctor has told you. The pharmacy label on your medicine will tell you how much to take, how often to take it and any special instructions.

How to take co-trimoxazole

  • Tablets – swallow the tablets with a glass of water. Do not chew them. 
  • Liquid – shake the medicine well. Measure the right amount using an oral syringe or medicine spoon. You can get these from your pharmacy. Do not use a kitchen spoon as it will not give you the right amount. Read more: Tips on how to give medicines to babies and children.
  • Timing: Co-trimoxazole is usually taken 2 times a day. Try to space the doses evenly throughout the day such as the first thing in the morning and at bedtime. Ideally these times should be at 12 hours apart. Co-trimoxazole is best taken with food.
  • Missed dose: If you forget to take your dose at the correct time, take one as soon as you remember. Try to take the correct number of doses each day, leaving 12 hours between doses. Do not take 2 doses at the same time to make up for a forgotten dose.
  • Alcohol: You can drink alcohol while taking co-trimoxazole.

It is important to take the whole course of antibiotics for the number of days your doctor has told you to. You should start to get better after taking co-trimoxazole for a few days. If you do not feel better or get more unwell, contact your doctor.

What to consider before starting co-trimoxazole

  • Are you pregnant or breast-feeding?
  • Do you have problems with your liver or kidneys?
  • Do you have asthma?
  • Have ever had an allergic reaction to a medicine, especially a sulphur antibiotic?
  • Are taking any other medicines? This includes any medicines you are taking that you can buy without a prescription, as well as herbal and complementary medicines.

If so, it’s important that you tell your doctor or pharmacist before you start co-trimoxazole. Sometimes a medicine isn’t suitable for a person with certain conditions or it can only be used with extra care.

Precautions while taking co-trimoxazole

  • It is important that you don't become dehydrated while you are taking co-trimoxazole. Try to drink a few glasses of water each day.
  • Protect yourself from too much sun and don't use sunbeds.
  • Store your co-trimoxazole tablets in a cool, dry place away from direct heat and light.
  • If you have been given liquid medicine, you may not need to keep it in the fridge – check the instructions on the bottle.
  • If your child is sick (vomits) and it is less than 30 minutes after having a dose of co-trimoxazole, give them the same dose again. But, if your child is sick (vomits) and it is more than 30 minutes after having a dose of co-trimoxazole, you do not need to give them another dose. Wait until the next normal dose.

What are the side effects of co-trimoxazole?

Like all medicines, co-trimoxazole can cause side effects, although not everyone gets them. Often side effects improve as your body gets used to the new medicine.

Side effects What should I do?
  • Nausea (feeling sick) or vomiting
  • Try taking co-trimoxazole with food.
  • Diarrhoea (loose, watery stools)
  • This may settle after a few days.
  • Tell your doctor if troublesome or if you become dehydrated.
  • Vaginal itching, soreness or discharge (thrush)
  • Mouth ulcers
  • Tell your doctor or pharmacist.
  • Allergic reaction such as skin rash, itching, swelling of the lips, face, and mouth or difficulty breathing
  • Stop taking co-trimoxazole.
  • Tell your doctor immediately or ring Healthline 0800 611 116.
Did you know that you can report a side effect to a medicine to CARM (Centre for Adverse Reactions Monitoring)? Report a side effect to a product


Co-trimoxazole interacts with some other medications and herbal supplements, so check with your doctor or pharmacist before starting co-trimoxazole.

Learn more

Medsafe Consumer Information Sheet Trisul


  1. Trimethoprim + sulfamethoxazole New Zealand Formulary

Additional resources for healthcare professionals

Co-trimoxazole NZ Formulary
Trisul Medsafe NZ
Deprim liquid Medsafe NZ
Upfront – antimicrobial resistance in New Zealand – what is my role in primary care? BPAC, NZ, 2013
Antibiotics guide BPAC, NZ, 2013

Credits: Sandra Ponen, Pharmacist. Reviewed By: Angela Lambie, Pharmacist, Auckland Last reviewed: 30 Oct 2018