Meds and you

Updated 11 February 2013


Flucloxacillin is a penicillin antibiotic.


Flucloxacillin is the active ingredient of Floxapen and Sandoz-Flucloxacillin.

Flucloxacillin is also one of multiple active ingredients found in Macropen, Megapen and Suprapen.

General information

Flucloxacillin is a penicillin antibiotic. It is prescribed for the treatment of a wide range of bacterial infections caused by susceptible organisms including soft-tissue infections such as boils or infections as a result of spider bites, ear infections, pneumonia, impetigo - a bacterial skin infection characterised by small pus-filled blisters, and endocarditis - inflammation of the lining of the heart and its valves.

Flucloxacillin, when prescribed on its own, is less effective than more commonly used penicillins when used to treat general penicillin-sensitive infections, and should preferably be reserved for the treatment of penicillin-resistant infections. It is often prescribed in combination with amoxicillin to provide an extended spectrum of efficacy.

Flucloxacillin can cause minor stomach upsets and a blotchy skin rash, a common unwanted effect which is not necessarily an indication of an allergic reaction. Should you develop a skin rash you should however consult your doctor to rule out the possibility of allergy. A penicillin allergy may lead to fever, swelling of the mouth and tongue, itching and associated breathing difficulties.

It is important to note that this medication is only effective against bacterial infections - if your infection is the result of a viral or fungal infection, it will be ineffective.

Antibiotic resistance - when bacteria develop the ability to defend themselves against the effect of an antibiotic - occurs frequently with many antibiotics. The most common causes of this are when patients do not complete the prescribed course in full, allowing bacteria to recover from treatment, and by using antibiotics for non-bacterial infections such as cold and flu.

Oral contraceptives may not be as effective as usual while taking flucloxacillin - other methods of contraception are advised to avoid unplanned pregnancy.

Flucloxacillin is best absorbed when taken on an empty stomach, and should preferably be taken one hour before, or 2 hours after a meal.

How does flucloxacillin work?

Flucloxacillin functions by changing the structure of the bacterial cell wall allowing fluid to penetrate into the cell. As a result the bacterial cell literally ruptures.

Fast facts

Drug schedule: schedule 4

Available as: flucloxacillin is available as capsules and as oral syrup

What does it do? flucloxacillin is an antibiotic

Overdose risk: low

Dependence risk: low

Is flucloxacillin available as a generic? yes

Is flucloxacillin available on prescription only? yes

User information

Onset of effect: it may take a few days for the full beneficial effect to be reached
Duration of action: up to 8 hours

Dietary advice: flucloxacillin is optimally absorbed when taken on an empty stomach, and should preferably be taken one hour before, or 2 hours after a meal.

Stopping this medicine: complete the full course as prescribed by your doctor, even if you feel better within a few days. Premature discontinuation may cause symptoms to recur, or cause bacterial resistance,

Prolonged use: flucloxacillin is usually given only for short courses of treatment. If prescribed for long term use your doctor may request periodic blood tests to monitor liver and kidney function.

Special precautions

Consult your doctor before using this drug if:

  • you are allergic to any penicillin or cephalosporin antibiotic
  • you have liver or kidney disease
  • you are taking any other medication

Pregnancy: avoid. Potential risk to the foetus has been reported. Consult your doctor before use, or if you are planning to fall pregnant.

Breastfeeding: avoid. It is unknown how this medication may affect your baby. Consult your doctor before use.

Porphyria: this medication is safe for use.

Infants and children: a reduced dose is advised and paediatric doses should be established by your paediatrician.

The elderly: no special precautions need to be taken.

Driving and hazardous work: no special precautions need to be taken.

Alcohol: no special precautions need to be taken.

Possible side effects

Side effect


Consult your doctor



Only if severe

In all cases

mild diarrhoea



nausea/ vomiting



abdominal pain



skin rash/ itch






swollen mouth/ tongue






unusual bruising







Drug interactions:

oral contraceptives

possible reduced contraceptive efficacy. another form of contraceptive is advised.


risk of flucloxacillin toxicity


increased risk of warfarin toxicity/bleeding

Disease interactions

Consult your doctor before using this drug if you are allergic to any penicillin or cephalosporin antibiotic, you have liver or kidney disease, or if you are taking any other medication.

Overdose action

A small overdose is no cause for concern. In case of intentional large overdose, seek emergency medical attention.

Recommended dosage

Adults: 250mg every 6 hours, with a maximum dose of 12g per day.

Paediatric doses should be established by your paediatrician.

This material is not intended to substitute medical advice, but is for informational purposes only. Please consult a physician for specific treatment and recommendations.


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