sulfamethoxazole + trimethoprim at a glance
Medicine class
A combination antibacterial containing a sulfonamide and trimethoprim.
Key specialist uses
Treatment or prevention of PJP and toxoplasmosis, and treatment of nocardiosis.
Other licensed uses
Selected susceptible urinary, middle-ear and respiratory infections when the combination is preferred to a single antibacterial.
Administration
Oral forms may be taken with food or drink to reduce stomach upset; maintain adequate fluid intake.
What is sulfamethoxazole + trimethoprim used for?
The selected products are licensed for infections caused by susceptible organisms. Choice should reflect microbiology and appropriate antibacterial use.
Treatment and prevention of Pneumocystis jirovecii pneumonia (PJP).
Treatment and prevention of toxoplasmosis.
Treatment of nocardiosis.
Selected acute uncomplicated urinary tract infections when there is evidence of susceptibility and a reason to prefer the combination.
Selected acute otitis media and acute exacerbations of chronic bronchitis under the same conditions.
How does sulfamethoxazole + trimethoprim work?
Sulfamethoxazole and trimethoprim block two successive steps that microbes use to make folate-related compounds needed for DNA production. Blocking the pathway at two points strengthens antibacterial activity against susceptible organisms.
sulfamethoxazole + trimethoprim preparations and strengths
Oral suspension
Route: Oral
Strengths: 40 mg + 200 mg/5 mL, 80 mg + 400 mg/5 mL
Tablet
Route: Oral
Strengths: 80 mg + 400 mg, 160 mg + 800 mg, 800 mg + 160 mg
How to take sulfamethoxazole + trimethoprim
Follow the product label and prescriber's instructions. Oral forms may be taken with food or drink if they upset the stomach.
Swallow tablets with water; their scoreline helps swallowing but does not divide them into equal amounts.
Measure oral suspension with the supplied measuring device rather than a household spoon.
Maintain adequate fluid intake unless a clinician has advised fluid restriction.
The infusion is diluted and administered intravenously by healthcare professionals.
sulfamethoxazole + trimethoprim side effects
Common or expected effects
- Nausea or diarrhoea
- Headache
- Rash
- Fungal overgrowth, such as thrush
- Raised blood potassium, often detected through testing
Get urgent medical advice
- Severe allergic reaction
- Blistering, peeling or widespread skin reaction
- Blood-cell disorders causing fever, sore throat, bruising, bleeding or marked weakness
- Liver injury, including jaundice
- New cough, breathlessness or other pulmonary hypersensitivity symptoms
- Severe electrolyte disturbance or kidney impairment
sulfamethoxazole + trimethoprim in pregnancy
The selected product information contraindicates use during the first trimester and advises avoiding it later unless clinically necessary. Trimethoprim interferes with folate pathways, while sulfamethoxazole near delivery may pose particular concern for babies at risk of raised bilirubin. Pregnancy, possible pregnancy or plans to conceive should be discussed promptly with the prescriber; folate supplementation may require consideration if treatment is essential.
sulfamethoxazole + trimethoprim while breastfeeding
Both components enter breast milk. Use requires clinical assessment and should be avoided where the mother or infant has, or is particularly prone to, raised bilirubin; the selected product information also advises avoidance in infants younger than eight weeks. Extra caution is needed with premature, jaundiced or otherwise unwell babies.
sulfamethoxazole + trimethoprim interactions
Check prescribed, over-the-counter and complementary products before treatment. Important interactions include:
Methotrexate
The combination can cause severe bone-marrow suppression and should usually be avoided, including shortly after methotrexate has stopped.
Warfarin
Anticoagulant activity may increase, requiring closer clotting surveillance and possible management changes.
Phenytoin
Phenytoin exposure may increase, raising the risk of toxicity and prompting clinical or concentration monitoring.
ACE inhibitors, angiotensin-receptor blockers and potassium-sparing diuretics
Common questions about sulfamethoxazole + trimethoprim
Answers are fully visible for fast scanning and source review.
Is sulfamethoxazole + trimethoprim the same as co-trimoxazole?
Yes. Co-trimoxazole is the established name for the combination of sulfamethoxazole and trimethoprim.
Is sulfamethoxazole + trimethoprim a penicillin antibiotic?
No. It combines a sulfonamide antibacterial with trimethoprim and does not belong to the penicillin class.
Why does sulfamethoxazole + trimethoprim contain two antibiotics?
Sources
These sources were used to prepare and review this medicine page.
Prepared and reviewed by the iatroX editorial team.