Macropen combines two penicillin antibiotics — flucloxacillin and amoxicillin — in one capsule or suspension. It is a prescription medicine used for infections where both Staphylococcus and other bacteria may be involved, such as skin, soft-tissue, ear, chest and dental infections.
What is Macropen?
Macropen is Schedule 4 — prescription-only:
| Product | Contains |
|---|---|
| Macropen capsule | Flucloxacillin 250 mg + amoxicillin 250 mg |
| Macropen S suspension | Flucloxacillin 125 mg + amoxicillin 125 mg |
This combination is generally known as co-fluampicil when made with ampicillin, and the principle is the same here.
Both ingredients are penicillins, but they cover different bacteria — which is the entire reason for combining them:
- Flucloxacillin is a penicillinase-resistant penicillin. Most Staphylococcus aureus produce an enzyme that destroys ordinary penicillins; flucloxacillin’s structure resists that enzyme, so it stays effective against staph. But its coverage is narrow — it does little against many other bacteria.
- Amoxicillin is a broad-spectrum penicillin, active against a wider range of organisms including streptococci and many Gram-negatives — but it is destroyed by the staph enzyme.
Each covers the other’s gap. Together they handle infections where the organism is uncertain and could be either — most obviously skin and soft-tissue infections, where staph and strep are both common.
Both work the same way: bacteria are enclosed by a rigid cell wall holding them against their own internal pressure, and penicillins block the enzymes that build and repair it, so the wall fails and the bacterium bursts. Human cells have no cell wall, which is why penicillins are selective and generally well tolerated.
This is a targeted combination rather than a broad one. It is not a substitute for co-amoxiclav, which solves a different problem — resistance from beta-lactamase-producing organisms generally.
What is Macropen commonly used for?
A doctor may prescribe it for:
- Skin and soft-tissue infections — cellulitis, infected wounds, boils, infected eczema — the most common use, since staph and strep are both likely.
- Infected bites and lacerations.
- Ear infections.
- Chest infections, in some cases.
- Dental infections, alongside dental treatment.
- Bone and joint infections, sometimes.
- Mixed or uncertain infections, where broader penicillin cover is wanted.
It has no effect on viruses. Colds, flu, most sore throats, most coughs and most bronchitis are viral, and an antibiotic will not shorten them.
How Macropen fits into this medicine category
| Group | Examples | Typical role |
|---|---|---|
| Anti-staphylococcal penicillins | Flucloxacillin | Skin infections caused by Staphylococcus |
| Broad-spectrum penicillins | Amoxicillin | Ear, chest, urinary, dental infections |
| Combined penicillins | Macropen | Where either organism could be responsible |
| Penicillin + inhibitor | Co-amoxiclav | Where beta-lactamase resistance is likely |
| Cephalosporins | Cefalexin | Skin, throat, urinary infections |
| Macrolides | Azithromycin | Chest infections, penicillin allergy |
| Nitroimidazoles | Metronidazole | Anaerobic and some parasitic infections |
See the antibiotics and antimicrobials hub.
What to check before using Macropen
Take it on an empty stomach — usually an hour before food or two hours after. This matters more than with most antibiotics, because flucloxacillin absorption is significantly reduced by food. Taking it with meals is a common reason it underperforms.
Tell your doctor about any penicillin allergy before you start. This is the most important check — both ingredients are penicillins, and a reaction can be severe. Describe what actually happened, since a childhood rash during a viral illness is frequently mislabelled as allergy and then steers people towards less suitable antibiotics for life.
Complete the full course, and take doses at evenly spaced intervals.
Tell your doctor or pharmacist if you:
- Have had any reaction to a penicillin or cephalosporin.
- Have had jaundice or liver problems on flucloxacillin before. This is a specific contraindication.
- Have liver or kidney disease.
- Are over 65, or having a long course — both raise the risk of the liver reaction described below.
- Have glandular fever (infectious mononucleosis), where amoxicillin commonly causes a widespread rash.
- Take warfarin, methotrexate, allopurinol or probenecid.
- Are pregnant or breastfeeding.
- Use the combined oral contraceptive pill. Antibiotics do not generally reduce its effectiveness, but severe vomiting or diarrhoea can.
Shake suspensions well, use the measuring device supplied, and check storage — most reconstituted suspensions must be refrigerated and discarded after a set number of days.
Possible cautions and when to ask a pharmacist or doctor
Common effects are nausea, diarrhoea, stomach upset and thrush (oral or vaginal).
Stop and seek medical attention urgently if you develop:
- Swelling of the face, lips, tongue or throat, difficulty breathing, or a widespread hives-like rash — a serious allergic reaction. Call emergency services.
- Any rash, which should be assessed rather than ignored.
- Blistering or peeling skin, or sores in the mouth or eyes.
- Yellowing of the eyes or skin, dark urine, pale stools or itching. This deserves emphasis: flucloxacillin is associated with a liver reaction (cholestatic jaundice) that is uncommon but well recognised, more likely in older people and with courses longer than two weeks, and — importantly — it can appear up to two months after finishing the course. Report it even if you stopped the antibiotic weeks ago.
- Severe, watery or bloody diarrhoea, during or in the weeks after the course — possible C. difficile infection, where anti-diarrhoeal medicines should not be used.
- Fever, sore throat or mouth ulcers, or unusual bruising or bleeding.
- Much less urine than usual.
- A seizure, which is rare and more likely with kidney impairment.
Contact your doctor if you are no better after two to three days, or if symptoms worsen at any point.
For a skin infection, watch the edge. If redness is spreading, the area is increasingly painful or swollen, red streaks appear, or you develop fever — seek medical attention promptly rather than waiting to finish the course.
Never use antibiotics left over from a previous illness or prescribed for someone else.
Related medicine guides
- Browse Antibiotics, Antifungals & Antimicrobials guides
- Read: Azrotrin used for
- Read: Metronidazole used for
Frequently asked questions
What are Macropen capsules used for? Bacterial infections where either Staphylococcus or other organisms may be responsible — commonly skin and soft-tissue infections, and also ear, chest and dental infections.
Why does it contain two antibiotics? Flucloxacillin covers staph but little else; amoxicillin covers a wider range but is destroyed by the staph enzyme. Each covers the other’s gap.
What is Macropen 500 used for? The same range of infections at a higher combined strength. Check your pack for the exact amounts of each ingredient.
Should I take it with food? No — take it on an empty stomach, about an hour before or two hours after eating. Food significantly reduces flucloxacillin absorption.
Is it the same as co-amoxiclav? No. Co-amoxiclav adds clavulanic acid to block a bacterial enzyme. Macropen combines two penicillins with different coverage.
Will it help flu or a cold? No. Those are viral, and antibiotics have no effect on them.
What if I get jaundice after finishing it? See a doctor. Flucloxacillin can cause a liver reaction that appears up to two months after the course, and it must be recorded so you are not given it again.
Can I stop when I feel better? No. Finish the prescribed course unless your doctor tells you otherwise.