Cloxin is cloxacillin, a penicillin antibiotic in 250 mg and 500 mg capsules. It is used for infections caused by staphylococcus — boils, abscesses, infected wounds, cellulitis, and bone and joint infections. It is a narrow, targeted antibiotic rather than a general-purpose one.
What is Cloxin?
Cloxin contains cloxacillin. The South African Medicine Price Registry lists two strengths, both Schedule 4 (prescription-only):
| Product | Form | Strength |
|---|---|---|
| Cloxin | Capsule | Cloxacillin 250 mg |
| Cloxin | Capsule | Cloxacillin 500 mg |
Cloxacillin is a penicillinase-resistant penicillin, and that phrase is the whole point of the medicine.
Ordinary penicillins are destroyed by an enzyme called penicillinase (beta-lactamase), which most strains of Staphylococcus aureus produce. That is why plain penicillin fails against most staph infections. Cloxacillin is chemically modified so the enzyme cannot break it down — the medicine survives and kills the bacterium.
Like other penicillins, it works by preventing bacteria from building their cell walls. Without an intact wall the organism cannot hold its shape and breaks apart.
The trade-off for that resistance is a narrow spectrum. Cloxacillin is very good against staphylococci and streptococci and does little against most other bacteria. That is a feature, not a limitation: a narrow antibiotic used for the right infection spares the rest of your normal bacteria and puts less pressure on resistance than a broad one.
The two strengths are the same medicine in different amounts. Severity, site of infection and body weight determine which is prescribed.
What is Cloxin commonly used for?
Cloxacillin is prescribed for staphylococcal infections, mainly of skin and soft tissue:
- Boils, carbuncles and abscesses.
- Infected wounds, cuts and surgical sites.
- Cellulitis — spreading infection of the skin and tissue beneath it.
- Impetigo, where it is widespread or not responding to a cream.
- Infected eczema.
- Bone and joint infections (osteomyelitis, septic arthritis), usually starting with intravenous treatment and continuing orally.
- Infected insect bites and burns.
- Mastitis — breast infection during breastfeeding.
- Some ear, sinus and chest infections where staphylococcus is the likely organism.
- Preventing infection around certain surgery.
It is not a general-purpose antibiotic. It does little for urinary tract infections, most chest infections, or infections caused by gram-negative bacteria. If it has been prescribed, it is because someone thinks staphylococcus is the problem — most often from the appearance of a skin infection, sometimes from a swab.
It will not help colds or flu, which are viral.
One important limitation: cloxacillin does not work against MRSA — methicillin-resistant Staphylococcus aureus — which by definition resists this whole group. An infection that is not improving on cloxacillin may be MRSA, and that needs a swab and a different antibiotic.
How Cloxin fits into this medicine category
| Group | Examples | Typical target |
|---|---|---|
| Penicillinase-resistant penicillins | Cloxacillin (Cloxin), flucloxacillin | Staphylococcal skin, soft tissue, bone infections |
| Aminopenicillins | Amoxicillin | Broad first-line cover: chest, ear, throat, urine |
| Penicillin + inhibitor | Co-amoxiclav | Where resistance enzymes defeat plain amoxicillin |
| Narrow penicillins | Phenoxymethylpenicillin | Streptococcal throat infection |
| Macrolides | Azithromycin (Azrotrin), erythromycin | Alternative in penicillin allergy |
| Nitroimidazoles | Metronidazole | Anaerobic and dental infections |
Cloxacillin and amoxicillin are both penicillins and are not interchangeable — they cover different organisms. See the antibiotics and antimicrobials hub.
What to check before using Cloxin
Penicillin allergy is the critical check. If you have ever reacted to penicillin, amoxicillin, cloxacillin, flucloxacillin or a cephalosporin, say so before the first dose. A previous mild reaction does not guarantee the next will be mild.
Also tell your doctor or pharmacist if you:
- Have liver disease or have had jaundice with a previous antibiotic, particularly flucloxacillin. Liver reactions are uncommon but recognised with this group and are more likely in older people and with longer courses.
- Have kidney disease.
- Take warfarin — antibiotics can affect anticoagulation control.
- Take methotrexate or probenecid.
- Are pregnant or breastfeeding. Cloxacillin is generally considered acceptable, but confirm with your clinician.
- Use the combined oral contraceptive pill and develop vomiting or diarrhoea during the course.
Practical points, and these matter more than usual with this medicine:
- Take it on an empty stomach — about an hour before food or two hours after. Cloxacillin is absorbed considerably less well with food, and taking it with meals can reduce the dose that actually reaches the infection.
- Space the doses evenly, usually four times a day. That is demanding, and it is the commonest way treatment fails.
- Swallow capsules with a full glass of water, sitting or standing upright.
- Complete the full course, even once the infection looks better. Skin infections that look settled on the outside can still be active underneath.
Possible cautions and when to ask a pharmacist or doctor
Common effects are nausea, diarrhoea, stomach discomfort and rash. Mild diarrhoea is usual with antibiotics because they disturb normal gut bacteria.
Get emergency help for:
- Swelling of the face, lips or tongue, difficulty breathing, widespread hives, or a rash with blistering or peeling — signs of a serious allergic reaction. Stop taking it.
- Severe, watery or bloody diarrhoea, especially with fever or cramping, during or in the weeks after the course. This can indicate Clostridioides difficile infection and needs assessment rather than an anti-diarrhoeal from the shelf.
- Yellowing of the skin or eyes, dark urine, pale stools, persistent nausea or right-sided abdominal pain — possible liver injury. This can appear up to several weeks after the course has finished.
Contact your doctor if:
- The infection is not improving after two to three days, or is spreading. Look for spreading redness, red streaks running from the area, increasing swelling or pain, or fever — those need same-day assessment.
- An abscess or boil is not draining. Antibiotics alone often will not clear a collection of pus; it may need to be drained.
- Infections keep recurring, which sometimes points to nasal carriage of staphylococcus or to an underlying condition such as diabetes.
- You develop thrush — oral or vaginal — after the course, which is common and easily treated.
Related medicine guides
Frequently asked questions
What is Cloxin 500 mg used for? Staphylococcal infections — boils, abscesses, infected wounds, cellulitis, infected eczema, mastitis, and bone and joint infections. It contains cloxacillin.
Is Cloxin the same as amoxicillin? No. Both are penicillins, but they cover different bacteria. Cloxacillin targets staphylococcus; amoxicillin is a broader first-line antibiotic.
Why must I take it on an empty stomach? Food significantly reduces how much cloxacillin is absorbed. Take it about an hour before eating or two hours after.
Can I take it if I am allergic to penicillin? No. Cloxacillin is a penicillin. Tell your prescriber so an alternative can be used.
Why four times a day? Cloxacillin does not stay in the body long, so evenly spaced doses keep levels high enough to work.
Will it treat a cold or flu? No. Those are viral and antibiotics have no effect on them.
Why isn’t my infection improving? It may be MRSA, which resists this antibiotic, or there may be pus that needs draining. Either way, go back to your doctor rather than continuing.
Can I stop when it looks better? Finish the course unless your doctor says otherwise. Skin infections can still be active beneath the surface.