Doctrim is a co-trimoxazole suspension, 240 mg per 5 ml — trimethoprim with sulfamethoxazole. It treats urinary, chest, ear and skin infections, and is given daily to prevent PCP pneumonia in people with weakened immunity, including HIV-exposed infants. Tell your prescriber about any sulfa allergy.
What is Doctrim?
Doctrim contains co-trimoxazole 240 mg per 5 ml — that figure is the combined total of its two ingredients:
- Trimethoprim 40 mg
- Sulfamethoxazole 200 mg
It is supplied as a suspension, which makes it the form usually given to children and to anyone who cannot manage tablets. It is a Schedule 4 prescription medicine, and the same combination is sold as Purbac, Troxazole, Novatrim and Bactrim.
The two ingredients block consecutive steps in one pathway. Bacteria must manufacture their own folate to build DNA — humans absorb it from food instead, so the pathway exists in the bacterium and not in us. Sulfamethoxazole blocks one enzyme in that chain and trimethoprim blocks the next. Interrupting a pathway at two consecutive points is far more effective than blocking either step alone, and makes resistance considerably harder to develop.
That the pathway does not exist in human cells is why the combination kills bacteria without a corresponding effect on us.
What is Doctrim commonly used for?
Treating infection:
- Urinary tract infections, including cystitis and kidney infections.
- Chest infections, including flare-ups of chronic bronchitis.
- Middle ear infections, particularly in children — a common use for the suspension.
- Skin and soft tissue infections, including some resistant staphylococcal infections.
- Certain gut infections, including shigellosis.
- Pneumocystis pneumonia (PCP), at much higher amounts.
Preventing infection:
- PCP prophylaxis in people with HIV, continued until the immune system recovers on antiretroviral treatment.
- In HIV-exposed infants, typically from six weeks of age until HIV infection has been excluded and breastfeeding has ended.
- In other immunosuppressed people, including some transplant recipients.
If a daily dose has been prescribed and the person is not unwell, that is the preventive use — and it is doing something important. PCP pneumonia is life-threatening when the immune system is weakened, and it develops fast. Feeling well is the intended result, not a reason to stop. Continue until a doctor says otherwise.
How Doctrim fits into this medicine category
| Group | Examples | Common targets |
|---|---|---|
| Sulfonamide combinations | Co-trimoxazole (Doctrim, Purbac) | Urinary, chest, ear, skin, PCP |
| Broad-spectrum penicillins | Amoxicillin | Chest, ear, throat, dental |
| Macrolides | Azithromycin | Chest, some STIs; penicillin allergy |
| Quinolones | Ciprofloxacin (Cifran) | Urinary, gut, prostate |
| Nitroimidazoles | Metronidazole | Anaerobic and dental infections |
No antibiotic is “strongest” in general — the right one depends on the organism, the site, allergies and local resistance patterns. See the antibiotics and antimicrobials hub.
What to check before using Doctrim
Say so if you have a sulfa allergy — before the first dose. Sulfonamide allergy is relatively common, reactions can be severe, and this is the most important check with this medicine.
Shake the bottle well and use the syringe or measure supplied, not a kitchen spoon. Paediatric amounts are calculated by weight and change as a child grows, so the dose is reviewed at clinic visits. Check whether the bottle needs refrigeration and how long it keeps once opened.
Finish a treatment course, and do not stop a preventive course because the person feels fine.
Drink plenty of water while taking it.
Tell your prescriber or pharmacist if:
- You have kidney or liver disease.
- You have G6PD deficiency, where sulfonamides can break down red blood cells.
- You have folate deficiency, or take methotrexate.
- You are pregnant, planning pregnancy or breastfeeding. It is generally avoided in the first trimester and near term.
- You take warfarin — co-trimoxazole markedly increases bleeding risk; phenytoin; an ACE inhibitor, ARB or spironolactone, where potassium can rise dangerously; or a diabetes tablet, where blood sugar can fall.
- The medicine is for an infant under 6 weeks, where it is not normally used.
Follow the dispensing label. This page does not set doses, and the amount for prevention differs greatly from the amount for treatment.
Possible cautions and when to ask a pharmacist or doctor
Take any rash seriously. Co-trimoxazole causes rash more often than most antibiotics. Most are mild, but it is also associated with the rare and very serious Stevens-Johnson syndrome and toxic epidermal necrolysis. Stop and seek medical help immediately for a rash that blisters or peels, sores in the mouth, eyes or genitals, or a widespread rash with fever. Do not wait to see whether it settles — and this applies to children as much as adults.
Potassium can rise, particularly in older adults, with reduced kidney function, or alongside ACE inhibitors, ARBs or spironolactone. Report muscle weakness or palpitations.
Blood counts can be affected with prolonged use. Report unusual bruising or bleeding, a sore throat, mouth ulcers or persistent fever.
Sun sensitivity is common — use sunscreen and cover up.
Nausea and reduced appetite are frequent; giving it with food helps.
In a child, report poor feeding, unusual drowsiness, a rash, jaundice or vomiting after doses.
Do not share it or keep leftovers. The right antibiotic depends on the infection, and unnecessary use drives resistance.
Seek urgent medical attention for a blistering or peeling rash, mouth or eye sores, swelling of the face or throat, difficulty breathing, unexplained bruising or bleeding, persistent high fever, severe or bloody diarrhoea, marked muscle weakness, yellowing of the skin or eyes, or a significant reduction in urine.
Related medicine guides
Frequently asked questions
What is Doctrim suspension used for? Urinary, chest, ear and skin infections, and — taken daily — preventing PCP pneumonia in people with weakened immunity, including HIV-exposed infants.
What does 240 mg per 5 ml mean? That is the combined total of the two ingredients: trimethoprim 40 mg plus sulfamethoxazole 200 mg.
Is it the same as Purbac or Bactrim? Yes. All are brands of co-trimoxazole.
Why is my child on it every day when they are not sick? That is preventive use, protecting against pneumonia that is dangerous when immunity is weakened. Do not stop until a doctor says so.
I am allergic to sulfa — can I take it? Tell your prescriber before taking any. Co-trimoxazole is a sulfonamide and reactions can be severe.
My child has developed a rash. What should I do? Contact the clinic. Stop and seek help immediately if it blisters or peels, involves the mouth or eyes, or comes with a fever.