Troxazole is co-trimoxazole — trimethoprim 80 mg with sulphamethoxazole 400 mg. It treats bacterial infections of the urinary tract, chest, skin and ears, and is used daily to prevent PCP pneumonia in people with a weakened immune system. Tell your prescriber about any sulfa allergy.
What is Troxazole?
Troxazole contains two antibiotics in one tablet:
- Trimethoprim 80 mg
- Sulphamethoxazole 400 mg
Together they are known as co-trimoxazole. The standard tablet totals 480 mg; a double-strength 960 mg tablet also exists. The same combination is sold as Purbac, Bactrim and Casra.
The pairing is not arbitrary. Bacteria have to build their own folate in order to make DNA — humans absorb folate from food instead, so the pathway exists in the bacterium and not in us. Sulphamethoxazole blocks one enzyme in that chain, and trimethoprim blocks the next one down. Interrupting a pathway at two consecutive points is far more effective than blocking either step alone, and it makes resistance considerably harder to develop.
That is also why the two are never sold separately for this purpose in South Africa: the combination is the medicine.
It is a Schedule 4 prescription medicine.
What is Troxazole commonly used for?
Treating infection:
- Urinary tract infections, including cystitis and kidney infections.
- Chest infections, including flare-ups of chronic bronchitis.
- Skin and soft tissue infections, including some resistant staphylococcal infections.
- Middle ear infections, particularly in children.
- Certain gut infections, including shigellosis and some travellers’ diarrhoea.
- Pneumocystis pneumonia (PCP), at higher amounts, where co-trimoxazole is the treatment of choice.
Preventing infection:
- PCP prophylaxis in people with HIV, typically when the CD4 count is below 200, continued until the immune system recovers on antiretroviral treatment such as Acriptega.
- Prophylaxis in other immunosuppressed people, including some transplant recipients.
- Prevention of recurrent urinary tract infections, in selected cases.
If you have been given a daily tablet and you are not unwell, that is the preventive use, and it is doing something important: preventing a pneumonia that is life-threatening when the immune system is weakened. It is meant to be taken every day for as long as the risk lasts. Feeling well is the intended result, not a sign it can stop.
How Troxazole fits into this medicine category
| Group | Examples | Common targets |
|---|---|---|
| Sulfonamide combinations | Co-trimoxazole (Troxazole, Purbac) | Urinary, chest, skin, PCP |
| Penicillins | Amoxicillin | Chest, ear, throat, dental |
| Macrolides | Azithromycin | Chest, some STIs, penicillin allergy |
| Quinolones | Ciprofloxacin | Urinary, gut, some resistant infections |
| Nitroimidazoles | Metronidazole | Anaerobic and dental infections |
No antibiotic is “strongest” in general — the right one depends on the organism, the site of infection, your allergies and local resistance patterns. See the antibiotics and antimicrobials hub.
What to check before using Troxazole
Say so if you have a sulfa allergy — before the first tablet. Sulfonamide allergy is relatively common, reactions can be severe, and this is the single most important check with this medicine. If you have ever reacted to something described as a “sulfa” drug, tell the prescriber and the pharmacist.
Finish a treatment course, and do not stop a preventive course because you feel 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 increases bleeding risk markedly; phenytoin; an ACE inhibitor, ARB or spironolactone, where potassium can rise dangerously; or a diabetes tablet, where blood sugar can drop.
- The medicine is for an infant under 6 weeks.
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 this medicine 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.
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, more so 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 outdoors.
Nausea and reduced appetite are frequent; taking it with food helps.
Do not share it, and do not keep leftovers for next time. The right antibiotic depends on the infection, and unnecessary use drives resistance — a particular concern with a combination this widely relied on in South Africa.
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 Troxazole used for? Bacterial infections — urinary, chest, skin, ear and some gut infections — and, taken daily, to prevent PCP pneumonia in people with a weakened immune system.
Is it the same as Purbac or Bactrim? Yes. All are brands of co-trimoxazole, trimethoprim plus sulphamethoxazole.
Why am I taking it every day when I am not sick? That is preventive use, protecting against a pneumonia that is dangerous when the immune system is weakened. Do not stop because you feel well.
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.
I have developed a rash. Should I keep taking it? Contact your prescriber. Stop and seek help immediately if it blisters or peels, involves the mouth or eyes, or comes with a fever.
Can I take it with warfarin? Only with medical direction. Co-trimoxazole substantially increases the effect of warfarin and the risk of bleeding.