Flucloxacillin
Is It Right for You?
A complete guide to Flucloxacillin — what it treats, how it works, dosages, side effects, and when a clinician may prescribe it following an online consultation.
What Is Flucloxacillin?
Flucloxacillin is a narrow-spectrum penicillin-type antibiotic used specifically to treat infections caused by staphylococcal bacteria, including strains that produce an enzyme called beta-lactamase. This enzyme is used by certain bacteria to destroy standard penicillins such as amoxicillin, rendering them ineffective. Flucloxacillin is structurally designed to resist this enzyme, making it the antibiotic of choice for skin, soft tissue, and bone infections caused by Staphylococcus aureus.
Introduced in the 1960s, flucloxacillin is firmly established in UK clinical practice and is available in capsule and liquid suspension forms for oral use, as well as as an injectable preparation for use in hospital settings. It is available generically and is sometimes referred to by older brand names such as Floxapen.
Flucloxacillin is a prescription-only medication in the UK. A licensed clinician must assess your symptoms and medical history before it can be prescribed – which can now be done quickly and conveniently through a telehealth consultation.
What Conditions Is Flucloxacillin Used For?
Flucloxacillin is prescribed for infections caused by beta-lactamase-producing staphylococci and other susceptible organisms:
cellulitis, impetigo, infected wounds, infected eczema, and folliculitis caused by Staphylococcus aureus.
abscesses and other deeper tissue infections caused by staphylococcal bacteria.
post-surgical or traumatic wound infections where staphylococci are the likely causative organism.
osteomyelitis (bone infection) and septic arthritis, often in combination with other antibiotics in hospital settings.
staphylococcal pneumonia, particularly post-influenza pneumonia where S. aureus is a known risk.
infection of the heart valves caused by staphylococci, typically managed in hospital.
bacterial outer ear infections caused by susceptible staphylococcal strains.
Flucloxacillin is not effective against meticillin-resistant Staphylococcus aureus (MRSA). If MRSA is suspected or confirmed, different antibiotics are required. A clinician will assess whether MRSA is a concern based on your history and circumstances.
How Does Flucloxacillin Work?
Like all penicillins, flucloxacillin belongs to the beta-lactam class of antibiotics. It works by binding to penicillin-binding proteins (PBPs) on the bacterial cell surface, interfering with the final stage of bacterial cell wall synthesis. Without a structurally sound cell wall, bacteria are unable to survive or replicate, and the cell wall eventually ruptures – killing the bacteria. This is known as a bactericidal mechanism.
What sets flucloxacillin apart from standard penicillins is its chemical structure: an isoxazolyl side chain shields the beta-lactam ring from being broken down by beta-lactamase enzymes secreted by Staphylococcus aureus and other resistant staphylococci. This makes flucloxacillin specifically effective against penicillinase-producing staphylococci that would otherwise destroy a standard penicillin antibiotic.
Flucloxacillin has a relatively narrow spectrum of activity and is not effective against Gram-negative bacteria, which is why it is used selectively when staphylococcal infection is confirmed or strongly suspected rather than as a broad-spectrum empirical antibiotic.
Dosages & Administration
The correct dose depends on the type and severity of infection, age, weight, and kidney function. Always follow your clinician's instructions. The table below is for general reference only.
Administration Tips
Flucloxacillin must be taken on an empty stomach – at least 30 to 60 minutes before food, or 2 hours after eating. Food significantly reduces the absorption of flucloxacillin, meaning the antibiotic may not reach effective levels in the body if taken with meals. This is one of the most important administration points and is frequently overlooked.
Take doses at evenly spaced intervals throughout the day to maintain consistent antibiotic levels. Four-times-daily dosing works best at intervals of approximately every 6 hours.
Shake liquid suspensions well before each use. Unused suspension should be stored in the refrigerator and discarded after 7–14 days (as directed on the label).
Always complete the full prescribed course even if symptoms improve quickly. Stopping early risks relapse and may contribute to antibiotic resistance.
Side Effects of Flucloxacillin
Most side effects are mild and resolve on their own. Serious side effects are rare but require prompt medical attention.
- Nausea
- Vomiting
- Diarrhoea
- Indigestion or stomach cramps
- Skin rash (mild)
- Oral thrush or vaginal yeast infection
- Severe allergic reaction (anaphylaxis) – hives, facial or throat swelling, difficulty breathing, collapse
- Cholestatic jaundice and hepatitis – flucloxacillin is associated with a rare but serious liver reaction that can occur during treatment or up to several weeks after completing the course; symptoms include jaundice (yellowing of the skin or eyes), dark urine, pale stools, and fatigue
- Stevens-Johnson Syndrome / Toxic Epidermal Necrolysis – rare but severe skin reactions with blistering and peeling
- C. difficile-associated diarrhoea – watery or bloody diarrhoea, abdominal cramping, fever
- Interstitial nephritis – inflammation of the kidneys, presenting with reduced urine output, swelling, or fever
- Haemolytic anaemia – destruction of red blood cells; symptoms include pallor, fatigue, and shortness of breath
If you have a confirmed allergy to penicillin or any other beta-lactam antibiotic, do not take flucloxacillin. Always disclose all known drug allergies before starting treatment. Patients with a history of penicillin allergy may require an alternative antibiotic such as clarithromycin or clindamycin.
Drug Interactions
Always disclose all prescription drugs, over-the-counter medicines, vitamins, and supplements to your clinician or pharmacist before starting flucloxacillin.
Flucloxacillin, like other penicillins, may reduce the kidney clearance of methotrexate, raising blood levels to potentially toxic concentrations. If both drugs must be used concurrently, close monitoring of methotrexate levels and renal function is essential.
Flucloxacillin can reduce the effectiveness of warfarin, potentially leading to subtherapeutic anticoagulation. The interaction is more likely with prolonged courses. INR should be monitored more frequently during and after a course of flucloxacillin in patients on warfarin.
As with other antibiotics, there is a theoretical risk of reduced contraceptive efficacy. Using a backup contraceptive method during the course is advisable as a precaution.
Reduces the kidney excretion of flucloxacillin, leading to higher and more prolonged blood levels. This interaction is sometimes used deliberately by clinicians to enhance antibiotic exposure, but it should not be used without medical supervision.
Antibiotics may reduce the immune response to live bacterial vaccines. Avoid vaccination during an antibiotic course unless clinically necessary.
Some evidence suggests that paracetamol may marginally increase flucloxacillin blood levels, though this is not considered clinically significant at standard doses. Inform your clinician if you are taking paracetamol regularly.
Important Warnings
Flucloxacillin is associated with a specific type of liver reaction – cholestatic hepatitis – that can occur during treatment or up to 8 weeks after finishing the course. While rare, it can be serious. Risk factors include older age, female sex, and prolonged courses. Contact your clinician immediately if you develop jaundice, dark urine, pale stools, or persistent fatigue after taking flucloxacillin.
Anaphylaxis has been reported with penicillin-class antibiotics, including flucloxacillin. Symptoms include sudden-onset hives, swelling of the throat or face, difficulty breathing, and collapse. Call 999 immediately and stop taking the medication if this occurs.
Like all antibiotics, flucloxacillin can disrupt the normal gut flora and allow Clostridioides difficile to overgrow, causing diarrhoea ranging from mild to life-threatening colitis. If you develop persistent or bloody diarrhoea during or after treatment, contact a clinician promptly. Do not take anti-diarrhoeal medications without medical advice.
Food significantly impairs absorption. Taking flucloxacillin with food can render it ineffective by preventing adequate drug levels from being reached. Always take at least 30 minutes before food or 2 hours after.
Flucloxacillin is generally considered safe to use during pregnancy when the benefits outweigh the risks, though data is more limited than for amoxicillin. It passes into breast milk in small amounts. Consult your clinician before starting treatment if you are pregnant or breastfeeding.
Patients with significantly reduced kidney function may require dose adjustments. Always disclose any history of kidney disease before starting flucloxacillin.
Speak to a Clinician About Treatment
Getting advice no longer means sitting in a waiting room. Through The GP Service, you can consult with a licensed clinician in minutes — from home, on your lunch break, or wherever works for you. If treatment is clinically appropriate, your clinician can issue a prescription during the consultation. A consultation does not guarantee a prescription.
The treatment you need, when you need it.
Flucloxacillin FAQs
Yes. A licensed clinician can assess your symptoms via a telehealth consultation and prescribe flucloxacillin if it is clinically appropriate. Prescriptions are typically sent to your preferred pharmacy the same day, often within minutes of your visit.
Most patients begin to notice an improvement in skin or soft tissue infection symptoms – such as reduced redness, swelling, and warmth – within 48 to 72 hours of starting treatment. If symptoms are worsening or not improving after 48 hours, contact your clinician.
Food significantly reduces the absorption of flucloxacillin from the gut, meaning less of the antibiotic reaches your bloodstream and the site of infection. Taking it at least 30 minutes before meals or 2 hours after ensures the drug is properly absorbed and can work effectively.
No. Both are penicillin-type antibiotics, but they target different bacteria. Amoxicillin is a broad-spectrum antibiotic effective against a wide range of bacteria, while flucloxacillin is specifically designed to treat penicillinase-producing staphylococci – bacteria that would destroy amoxicillin. They are used for different types of infection.
No. Flucloxacillin is not effective against MRSA (meticillin-resistant Staphylococcus aureus). MRSA requires specialist antibiotics. If MRSA is suspected – for example in patients with a history of MRSA or in healthcare settings – a clinician will arrange appropriate testing and treatment.
Both are forms of hyoscine, but they have very different pharmacological profiles. Hyoscine hydrobromide (scopolamine) crosses the blood-brain barrier and produces central anticholinergic effects including sedation, anti-nausea effects, and — at toxic doses — confusion and hallucinations. It is used for travel sickness and as a pre-anaesthetic. Hyoscine butylbromide does not cross the blood-brain barrier significantly, acts only peripherally on smooth muscle, and causes no central effects. It is safer and more targeted for gastrointestinal conditions.
There is no known dangerous interaction between alcohol and flucloxacillin. However, alcohol can impair the immune system and slow recovery from infection. It is generally advisable to avoid or minimise alcohol consumption while you are unwell and taking antibiotics.
Standard Buscopan tablets contain 10 mg of hyoscine butylbromide and are available over the counter for self-treatment of IBS and abdominal cramps. Buscopan Forte (or prescription-strength formulations) contain 20 mg and are available on prescription for more severe spasm. Your clinician will advise on the appropriate dose and strength for your condition.
Yes. Flucloxacillin is used in children and is available in liquid suspension form. Doses are calculated based on the child's weight and age. Always follow the clinician's instructions precisely for paediatric dosing.
A recurrent or returning infection after a completed course may indicate that the bacteria were not fully eradicated, that a different organism is responsible, or that there is an underlying cause such as a wound that needs attention. Contact your clinician for reassessment rather than requesting a repeat course without evaluation.