Purbac is co-trimoxazole — sulfamethoxazole plus trimethoprim — in 480 mg and 960 mg tablets. It treats bacterial infections including urinary, chest and skin infections, and is widely used in South Africa to prevent PCP pneumonia in people with HIV. Finish the full course.
What is Purbac?
Purbac contains two antibiotics working together:
- Sulfamethoxazole 400 mg
- Trimethoprim 80 mg
That combination is called co-trimoxazole. The standard tablet is 480 mg total; the double-strength tablet is 960 mg.
The two ingredients block consecutive steps in the same pathway. Bacteria must manufacture their own folate to build DNA — unlike humans, who absorb it from food. Sulfamethoxazole blocks one step in that manufacture and trimethoprim blocks the next. Interrupting a pathway at two points is far more effective than at one, and it also makes resistance slower to develop.
That the pathway does not exist in human cells is why the combination can kill bacteria without a corresponding effect on us.
Co-trimoxazole holds a particular place in South African medicine. Beyond treating infections, it is given preventively to people with HIV whose CD4 count is low, where it substantially reduces deaths from opportunistic infection. It is a Schedule 4 prescription medicine.
What is Purbac commonly used for?
Purbac is prescribed both to treat infection and to prevent it.
Treating infections:
- Urinary tract infections, including cystitis and kidney infections.
- Chest infections, including exacerbations of chronic bronchitis.
- Skin and soft tissue infections, including some resistant Staphylococcus infections.
- Middle ear infections, particularly in children.
- Some gut infections, including shigellosis and travellers’ diarrhoea.
- Pneumocystis pneumonia (PCP), at higher amounts, where it is the treatment of choice.
Preventing infection:
- PCP prophylaxis in people with HIV, typically where the CD4 count is below 200, continued until immune recovery on antiretroviral therapy.
- Prophylaxis in other immunosuppressed people, including some transplant recipients and those on certain immune-suppressing treatments.
- Prevention of recurrent urinary tract infections, in some cases.
The preventive use is the one most often misunderstood. Someone taking a daily tablet is often not treating anything — they are preventing a pneumonia that can be life-threatening in someone with a weakened immune system. It is meant to be taken every day, indefinitely, while the risk lasts, and stopping because you feel well removes exactly the protection it exists to provide. Alongside antiretrovirals such as Acriptega, this pairing has saved an enormous number of lives.
How Purbac fits into this medicine category
Co-trimoxazole belongs to the sulfonamide group:
| Group | Examples | Common targets |
|---|---|---|
| Sulfonamide combinations | Co-trimoxazole (Purbac) | Urinary, chest, skin, PCP |
| Penicillins | Amoxicillin, amoxicillin-clavulanate | Chest, ear, throat, dental |
| Macrolides | Azithromycin, clarithromycin | Chest, some STIs, penicillin allergy |
| Quinolones | Ciprofloxacin | Urinary, gut, some resistant infections |
| Nitroimidazoles | Metronidazole | Anaerobic and dental infections |
Which antibiotic is right depends on the organism, the site, allergies and local resistance patterns — not on which is “strongest”. See the antibiotics and antimicrobials hub.
What to check before using Purbac
Finish the full course for a treatment prescription, even once you feel better. And do not stop a preventive course because you feel well — that is the point of it.
Drink plenty of water while taking it.
Tell your prescriber or pharmacist if:
- You have a sulfa allergy. Sulfonamide allergy is relatively common and reactions can be severe. If you have ever reacted to a “sulfa” medicine, say so before the first tablet.
- You have kidney or liver disease.
- You have G6PD deficiency, where sulfonamides can cause red blood cells to break down.
- You have a folate deficiency, or are on methotrexate.
- You are pregnant, planning pregnancy or breastfeeding. It is generally avoided in the first trimester and near term.
- You take warfarin — co-trimoxazole raises bleeding risk considerably; phenytoin; methotrexate; 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.
Follow the dispensing label. This page does not set doses, and the amount differs sharply between prevention and treatment.
Possible cautions and when to ask a pharmacist or doctor
Rash needs attention, not tolerance. Co-trimoxazole causes rash more often than most antibiotics, and while most rashes are mild, this medicine is also associated with the rare but very serious Stevens-Johnson syndrome and toxic epidermal necrolysis. Stop and seek medical help immediately for a rash with blistering, peeling, sores in the mouth, eyes or genitals, or a widespread rash with fever.
Potassium can rise, particularly in older people, those with kidney impairment, and those on ACE inhibitors, ARBs or spironolactone. Muscle weakness or palpitations should be reported.
Blood counts can be affected with prolonged use. Report unusual bruising, bleeding, sore throat, mouth ulcers or persistent fever.
Sun sensitivity is common — use sunscreen and cover up.
Nausea and reduced appetite are frequent and usually manageable by taking it with food.
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, facial or throat swelling, 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 Purbac 480 mg used for? Bacterial infections — urinary, chest, skin, ear and some gut infections — and, taken daily, to prevent PCP pneumonia in people with HIV or other immune suppression.
Why am I on it every day if I am not sick? That is preventive use. A daily tablet protects against pneumonia that can be life-threatening when the immune system is weakened. Do not stop because you feel well.
Is it an antibiotic? Yes — two antibiotics in one tablet, sulfamethoxazole and trimethoprim, together called co-trimoxazole.
What is the difference between 480 mg and 960 mg? The strength. 960 mg is the double-strength tablet. Your prescriber chooses based on the purpose.
I have a sulfa allergy — 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. What should I do? Contact your prescriber. Seek help immediately if it blisters or peels, involves the mouth or eyes, or comes with a fever.