co-trimoxazole at a glance
Medicine class
Combination antibacterial containing trimethoprim and a sulfonamide.
Licensed roles
Selected urinary infections, Pneumocystis jirovecii pneumonia, toxoplasmosis and nocardiosis.
Important checks
Kidney function, electrolytes and blood counts may require monitoring, particularly during prolonged or higher-risk treatment.
What is co-trimoxazole used for?
The selected intravenous product is licensed for susceptible organisms in adults and children older than six weeks.
Acute uncomplicated urinary tract infection
Treatment and prevention of Pneumocystis jirovecii pneumonia
Treatment and prevention of toxoplasmosis
Nocardiosis
How does co-trimoxazole work?
Sulfamethoxazole and trimethoprim block two consecutive stages of microbial folate production, disrupting the formation of genetic material needed by susceptible organisms.
co-trimoxazole preparations and strengths
Solution for infusion
Route: Intravenous
Strengths: 16 mg + 80 mg/mL
How to take co-trimoxazole
The selected formulation is diluted and given into a vein by a healthcare professional. If oral co-trimoxazole is prescribed, follow its label. Food and water may reduce stomach upset, and adequate hydration is important.
The infusion must be diluted before administration.
Tell the clinical team promptly if pain, swelling or another reaction develops during an infusion.
co-trimoxazole side effects
Common or expected effects
- Nausea or diarrhoea
- Headache
- Skin rash
- Thrush or another fungal overgrowth
- Raised blood potassium
Get urgent medical advice
- Severe allergic reaction
- Blistering or peeling skin reactions or mucosal sores
- Blood disorders causing fever, sore throat, marked tiredness, bruising or bleeding
- Liver injury causing yellow skin or eyes
- New cough, breathlessness or worsening lung function
- Severe electrolyte disturbance, including hyperkalaemia
- Kidney inflammation or impaired kidney function
co-trimoxazole in pregnancy
The selected infusion is contraindicated during the first trimester and should generally be avoided later unless clinically necessary. Specialist assessment and consideration of folic acid supplementation are important if treatment is essential. Use near delivery also requires consideration of neonatal jaundice risk.
co-trimoxazole while breastfeeding
Trimethoprim and sulfamethoxazole pass into breast milk. A prescriber should assess the infant’s age and health. The selected infusion should be avoided when the infant is younger than eight weeks or when the mother or infant has, or is at particular risk of, raised bilirubin, including jaundice.
co-trimoxazole interactions
Check all prescribed, over-the-counter and complementary products before treatment. Important interactions include:
Methotrexate
Avoid combining them because severe, sometimes delayed bone-marrow suppression can occur.
Warfarin
Anticoagulation and bleeding risk may increase, requiring closer monitoring.
ACE inhibitors, angiotensin-receptor blockers and potassium-sparing diuretics
Clinically important hyperkalaemia can occur, so potassium monitoring may be required.
Common questions about co-trimoxazole
Answers are fully visible for fast scanning and source review.
What is co-trimoxazole made from?
It combines trimethoprim and sulfamethoxazole.
Is co-trimoxazole a penicillin?
No. It is a trimethoprim–sulfonamide combination, although serious allergic reactions can still occur.
Can co-trimoxazole cause a serious skin rash?
Sources
These sources were used to prepare and review this medicine page.
Prepared and reviewed by the iatroX editorial team.