Lagatrim is co-trimoxazole — sulfamethoxazole 400 mg with trimethoprim 80 mg. It treats urinary, chest, ear and some skin and gut infections, and it has a second role that matters enormously in South Africa: preventing serious infections in people living with HIV and in infants exposed to HIV.
What is Lagatrim?
The South African Medicine Price Registry lists Lagatrim as a Schedule 4 tablet containing sulfamethoxazole 400 mg and trimethoprim 80 mg — the combination known as co-trimoxazole. A double-strength tablet (800/160 mg) and a paediatric suspension exist under this and other brand names, including Bactrim and Purbac.
The 480 mg people search for is the two ingredients added together: 400 mg sulfamethoxazole plus 80 mg trimethoprim.
The two work in sequence on the same pathway, which is what makes the combination effective.
Bacteria must manufacture their own folate — they cannot absorb it from their surroundings the way human cells do. Sulfamethoxazole blocks the first step of that manufacturing process, and trimethoprim blocks a later one. Interrupting the same production line at two points is far more effective than blocking either alone, and it makes resistance harder to develop.
Because human cells take folate from the diet rather than making it, they are largely unaffected — which is why a medicine that starves bacteria of an essential vitamin is nonetheless usable. But not entirely unaffected, which is why folate deficiency, and effects on blood counts, appear among its cautions.
Sulfamethoxazole is a sulfonamide — a “sulfa” drug. Sulfa allergy is relatively common and sometimes serious, which is the single most important thing to establish before anyone takes this medicine.
What is Lagatrim commonly used for?
As treatment:
- Urinary tract infections, including cystitis and some kidney infections — one of its commonest uses.
- Chest infections, including bronchitis and some pneumonias.
- Middle ear infections, particularly in children.
- Sinusitis.
- Traveller’s diarrhoea and some gut infections, including shigella.
- Skin infections, including some caused by resistant Staphylococcus aureus.
- Prostate infections, where it penetrates well.
As prevention — and this is where it matters most in South Africa:
- **Preventing Pneumocystis jirovecii pneumonia (PCP)** in people with HIV and a low CD4 count. This is its most important single use. PCP was a leading cause of death in advanced HIV, and co-trimoxazole prophylaxis prevents it highly effectively.
- Preventing other infections in advanced HIV, including toxoplasmosis and some bacterial infections. It reduces overall mortality, which few preventive medicines can claim.
- In HIV-exposed infants, given from around six weeks of age until HIV infection is excluded and breastfeeding has ended. This is standard South African practice.
- In people on immunosuppressive treatment, after transplant, or on chemotherapy.
If you are taking it as prevention, take it every day as prescribed, indefinitely, even when you feel completely well. This is the point most often lost. It is not treating anything you can feel — it is stopping something serious from starting. Stopping it because you feel fine removes the protection precisely when it is doing its job. Your doctor will say when it can be stopped, usually once the CD4 count has recovered on antiretroviral treatment.
It does nothing for viral infections — colds, flu, most sore throats.
How Lagatrim fits into this medicine category
| Group | Examples | Typical use |
|---|---|---|
| Sulfonamide + trimethoprim | Co-trimoxazole (Lagatrim) | UTIs, chest, ear; HIV prophylaxis |
| Penicillins | Amoxicillin, co-amoxiclav | Common first-line infections |
| Macrolides | Azithromycin | Chest infections; penicillin allergy |
| Nitrofurans | Nitrofurantoin | Simple urinary infections |
| Nitroimidazoles | Metronidazole | Anaerobic and dental infections |
| Tetracyclines | Doxycycline | Chest, skin, tick-bite fever |
| Quinolones | Ciprofloxacin | Reserved; significant side effects |
Co-trimoxazole is an old medicine that has not been superseded. Resistance has reduced its usefulness for routine urinary infections in some settings, but its role in HIV-related prophylaxis is unmatched and its place in South African treatment guidelines is firmly established.
See the antibiotics and antimicrobials hub.
What to check before using Lagatrim
Tell your doctor or pharmacist about any sulfa allergy. This is the most important check. A previous reaction to co-trimoxazole, Bactrim, Purbac or any “sulfa” medicine means this should not be given. If the reaction involved a widespread rash, blistering, mouth ulcers, fever or breathing difficulty, say so clearly — those reactions can be severe and can recur worse.
Also tell them if you:
- Have kidney disease or liver disease.
- Have G6PD deficiency, where co-trimoxazole can cause red blood cells to break down.
- Have a blood disorder, low blood counts, or folate deficiency.
- Have asthma or severe allergies.
- Take warfarin — a significant interaction that raises INR and bleeding risk.
- Take methotrexate. Both affect folate, and the combination can cause serious toxicity.
- Take phenytoin, an ACE inhibitor or ARB, spironolactone, or potassium supplements. Co-trimoxazole raises potassium, and combined with these it can rise dangerously.
- Take digoxin, ciclosporin, rifampicin, or diabetes tablets such as glibenclamide.
- Are elderly — side effects, high potassium and blood count problems are all more likely.
- Are pregnant, planning pregnancy or breastfeeding. It is generally avoided in the first trimester and near term, though it may still be used in HIV where the benefit is clear. Folic acid is often given alongside.
- Are giving it to a young infant — under six weeks it is generally avoided outside specific HIV protocols.
Practical points:
- Drink plenty of water throughout the course. This helps protect the kidneys.
- Take doses evenly spaced, with or after food to reduce stomach upset.
- Complete a treatment course; continue a preventive course indefinitely as directed.
- Use sun protection. Co-trimoxazole makes skin considerably more sensitive to sunlight.
Possible cautions and when to ask a pharmacist or doctor
Common effects are nausea, vomiting, loss of appetite, diarrhoea and rash.
A rash deserves particular attention with this medicine. Most rashes are mild, but co-trimoxazole is one of the medicines most associated with severe skin reactions — Stevens-Johnson syndrome and toxic epidermal necrolysis. These are rare, but they begin as an ordinary-looking rash.
Stop taking it and get medical help the same day for any new rash. Do not wait to see how it develops.
Get emergency help for:
- A rash with blistering, peeling skin, or sores in the mouth, eyes or genitals.
- A rash with fever, swollen glands or feeling very unwell.
- Swelling of the face, lips or tongue, or difficulty breathing.
- Severe or bloody diarrhoea, during or after the course.
- Yellowing of the skin or eyes.
- Unusual bruising, bleeding, or small purple spots in the skin, or a sore throat with fever — these can indicate a fall in blood counts.
- Marked weakness, palpitations or an irregular heartbeat — possible high potassium.
- Confusion, seizures, or a marked reduction in urine output.
Contact your doctor if:
- You are no better after two to three days of treatment, or are getting worse.
- You develop any rash, however mild it looks.
- You are on long-term prevention and want to stop, or are struggling with side effects — there are alternatives, and stopping without one leaves you unprotected.
- You are pregnant or planning pregnancy while on long-term treatment.
- Another prescriber starts you on a new medicine, particularly warfarin, methotrexate, or anything affecting potassium.
Related medicine guides
Frequently asked questions
What is Lagatrim 480 mg used for? Urinary, chest, ear, sinus and some skin and gut infections — and, importantly, preventing Pneumocystis pneumonia and other serious infections in people living with HIV. 480 mg is the two ingredients combined: sulfamethoxazole 400 mg plus trimethoprim 80 mg.
Is Lagatrim the same as Bactrim or Purbac? Yes. All are brands of co-trimoxazole with the same two ingredients.
Why do I take it every day if I am not sick? Because it is preventing infection rather than treating one. In HIV, daily co-trimoxazole prevents Pneumocystis pneumonia and reduces deaths. Your doctor will say when it can stop.
Can I take it if I am allergic to sulfa? No. Tell your doctor — an alternative is needed.
What should I do if I get a rash? Stop taking it and get medical advice the same day. Most rashes are mild, but this medicine is associated with rare severe skin reactions that start looking ordinary.
Does it interact with warfarin? Yes, significantly. It raises INR and bleeding risk, and your monitoring will need adjusting.
Can I take it in pregnancy? Discuss it. It is generally avoided in the first trimester and near term, but may still be used in HIV where the benefit is clear — usually with folic acid.
Why must I avoid sun? Co-trimoxazole makes skin considerably more sensitive to sunlight. Use sunscreen and cover up.