A penicillin antibiotic
Flucloxacillin
A penicillin antibiotic used mainly for skin and soft-tissue infections, best taken on an empty stomach — not for anyone allergic to penicillin.
What is Flucloxacillin?
Flucloxacillin is a penicillin antibiotic used mainly for skin and soft-tissue infections such as cellulitis, infected wounds and impetigo. It is particularly suited to infections caused by certain staphylococcal and streptococcal bacteria.
Education and reference only. This is a plain-language guide to Flucloxacillin — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Flucloxacillin is a penicillin antibiotic used mainly for skin and soft-tissue infections such as cellulitis, infected wounds, boils and impetigo, because it is particularly good against the staphylococcus and streptococcus bacteria that cause them. It is also used in some bone, joint and other infections. It is taken as a short course just long enough to clear the infection, and works only against bacteria — not viruses.
How it works
Flucloxacillin attacks the cell wall that bacteria need to hold themselves together. By stopping the bacteria from building and repairing this wall, the medicine causes them to break apart and die, allowing the body to clear the infection. It is designed to resist an enzyme (penicillinase) that some staphylococcus bacteria use to inactivate ordinary penicillins, which is why it is a good choice for skin infections caused by these bugs. It is absorbed better on an empty stomach, so it works best taken before food.
Company & origin
Originated / developed by: Beecham Research Laboratories (now GSK).
Flucloxacillin is a penicillinase-resistant semisynthetic penicillin developed by Beecham Research Laboratories in the UK in the 1960s (patented around 1961) and marketed in the early 1970s as Floxapen. Beecham is now part of GSK.
Practical use
How to take Flucloxacillin
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it on an empty stomach, about an hour before food or two hours after, as food reduces how well it is absorbed.
- Complete the whole course as prescribed, even once the infection looks better, to fully clear it.
- Space the doses evenly through the day and drink plenty of water with each one.
- If you miss a dose, take it as soon as you remember unless the next is nearly due, then carry on; do not double up.
- Report any yellowing of the skin or eyes, dark urine or pale stools, as flucloxacillin can rarely affect the liver.
Weighing it up
Advantages & disadvantages of Flucloxacillin
Advantages
- Well targeted to common skin and soft-tissue infections.
- Reliable against many staphylococcal infections, including most non-resistant strains.
- Long-standing UK first-line choice for cellulitis and similar infections.
- Available in forms that can be taken at home by mouth.
Disadvantages
- Must be taken on an empty stomach, which can be inconvenient.
- Cannot be used by people with a penicillin allergy.
- Can rarely cause liver problems, sometimes appearing after the course has finished.
- May cause nausea, diarrhoea or thrush like other antibiotics.
Practical use
Good to know
A practical point that catches people out: flucloxacillin is best taken on an empty stomach — usually before food — because food reduces how much is absorbed. It is taken as a short course and should be taken exactly as prescribed and finished as advised, as part of using antibiotics responsibly (antimicrobial stewardship). As with all penicillins, the key safety rule is allergy: it must not be taken by anyone allergic to penicillin. Importantly, flucloxacillin can rarely cause a delayed liver problem (jaundice and liver inflammation) that may appear up to several weeks after the course has finished — so any yellowing of the skin or eyes, dark urine or itching should be reported, even after you have stopped taking it.
Who should not take it / use with caution
- Anyone allergic to penicillin or any penicillin antibiotic — the key safety rule.
- Anyone who has previously had jaundice or a liver reaction caused by flucloxacillin must not take it again.
- Used with care, and the dose adjusted, in people with significant liver problems or significant kidney impairment, and in older people who can be more vulnerable to the liver effect.
Monitoring
- Whether the infection is improving
- For signs of a liver reaction (jaundice, dark urine, itching) during and for some weeks after the course
- For any sign of allergy
Side effects
- Stomach upset, feeling sick or loose stools — common and usually mild.
- Thrush (a fungal overgrowth) in the mouth or vagina.
- Rarely but importantly, a delayed liver reaction — jaundice (yellow skin or eyes), dark urine, pale stools or itching — which can begin even weeks after finishing the course and should be reported promptly; and, very rarely, a serious allergic reaction (call 999 for swelling of the face or throat, wheeze or collapse).
Key interactions
- It can occasionally enhance the effect of warfarin, so anticoagulant monitoring may be needed.
- Methotrexate levels can rise when taken alongside penicillins, which needs care.
- Certain other medicines can interact; tell your pharmacist what else you take. Some medicines that affect the liver may add to the risk if used around the same time.
Available as: Capsules and an oral suspension (liquid) for those who cannot swallow capsules; also given by injection in hospital.
Answers
Flucloxacillin: frequently asked questions
Why do I have to take flucloxacillin on an empty stomach?
Food reduces how much flucloxacillin your body absorbs, so it works best taken on an empty stomach — generally before food, with a drink of water. Following this timing helps make sure enough of the medicine reaches the infection.
What is this liver warning about?
Flucloxacillin can, rarely, trigger a delayed reaction in the liver. The important point is that it can appear up to several weeks after you have finished the course. If you notice yellowing of the skin or the whites of your eyes, dark urine, pale stools, unusual tiredness or itching — even after stopping — contact a doctor promptly and mention you have recently taken flucloxacillin.
Can I take it if I am allergic to penicillin?
No. Flucloxacillin is a penicillin, so it must not be taken by anyone with a penicillin allergy. Make sure the allergy is recorded and mention it whenever an antibiotic is being considered.
Should I finish the course even if my skin looks better?
Yes — take it exactly as prescribed and finish the course as advised. Skin and soft-tissue infections can flare back if treatment is cut short, and completing the agreed course is part of using antibiotics responsibly. Speak to your prescriber if side effects are a problem rather than simply stopping.
What is the difference between flucloxacillin and Floxapen?
They are the same medicine — flucloxacillin is the generic (active-ingredient) name and Floxapen is a brand name. Generic flucloxacillin contains the identical active ingredient.
The wider class
About Penicillins
Flucloxacillin belongs to the penicillins class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
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Authoritative sources
- BNF: Flucloxacillin.
- electronic Medicines Compendium (SmPC): Flucloxacillin.
- NICE CKS: Flucloxacillin.
- MHRA Drug Safety Update: Flucloxacillin and liver injury.
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