Flucloxacillin

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Antibiotic derived from Penicillin

title: "Flucloxacillin" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["penicillins", "enantiopure-drugs", "hepatotoxins", "isoxazoles", "2-chlorophenyl-compounds", "2-fluorophenyl-compounds"] description: "Antibiotic derived from Penicillin" topic_path: "general/penicillins" source: "https://en.wikipedia.org/wiki/Flucloxacillin" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Antibiotic derived from Penicillin ::

::data[format=table title="Infobox drug"]

FieldValue
Watchedfieldschanged
verifiedrevid461101078
imageFlucloxacillin skeletal formula labelled.svg
image_classskin-invert-image
image2Flucloxacillin-from-xtal-1980-3D-balls.png
image_class2bg-transparent
tradenameFloxapen, others
Drugs.com
DailyMedID
pregnancy_AUB1
routes_of_administrationBy mouth, intramuscular, intravenous, intrapleural, intraarticular
ATC_prefixJ01
ATC_suffixCF05
legal_AUS4
legal_AU_comment
legal_BR
legal_CA
legal_DE
legal_NZPrescription only
legal_UKPOM
legal_US
legal_EURx-only
legal_EU_comment
legal_UN
legal_status
bioavailability50–70%
metabolismLiver
elimination_half-life0.75–1 hour
excretionKidney
CAS_number_Ref
CAS_number5250-39-5
UNII_Ref
UNII43B2M34G2V
PubChem21319
IUPHAR_ligand10910
DrugBankDB00301
ChemSpiderID20037
KEGGD04196
ChEBI5098
ChEMBL222645
synonymsBRL-2039
IUPAC_name(2S,5R,6R)-6-({[3-(2-chloro-5-fluorophenyl)-5-methylisoxazol-4-yl]carbonyl}amino)-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-2-carboxylic acid
C19
SMILESO=C(O)[C@@H]3N4C(=O)C@@H[C@H]4SC3(C)C
StdInChI_Ref
StdInChI1S/C19H17ClFN3O5S/c1-7-10(12(23-29-7)11-8(20)5-4-6-9(11)21)15(25)22-13-16(26)24-14(18(27)28)19(2,3)30-17(13)24/h4-6,13-14,17H,1-3H3,(H,22,25)(H,27,28)/t13-,14+,17-/m1/s1
StdInChIKey_Ref
StdInChIKeyUIOFUWFRIANQPC-JKIFEVAISA-N
::

| Watchedfields = changed | verifiedrevid = 461101078 | image = Flucloxacillin skeletal formula labelled.svg | image_class = skin-invert-image | alt = | image2 = Flucloxacillin-from-xtal-1980-3D-balls.png | image_class2 = bg-transparent | alt2 = | caption =

| pronounce = | tradename = Floxapen, others | Drugs.com = | MedlinePlus = | DailyMedID = | pregnancy_AU = B1 | pregnancy_AU_comment = | pregnancy_category= | routes_of_administration = By mouth, intramuscular, intravenous, intrapleural, intraarticular | class = | ATC_prefix = J01 | ATC_suffix = CF05 | ATC_supplemental =

| legal_AU = S4 | legal_AU_comment = | legal_BR = | legal_BR_comment = | legal_CA = | legal_CA_comment = | legal_DE = | legal_DE_comment = | legal_NZ = Prescription only | legal_UK = POM | legal_UK_comment = | legal_US = | legal_US_comment = | legal_EU = Rx-only | legal_EU_comment = | legal_UN = | legal_UN_comment = | legal_status =

| bioavailability = 50–70% | protein_bound = | metabolism = Liver | metabolites = | onset = | elimination_half-life = 0.75–1 hour | duration_of_action = | excretion = Kidney

| CAS_number_Ref = | CAS_number = 5250-39-5 | UNII_Ref = | UNII = 43B2M34G2V | CAS_supplemental = | PubChem = 21319 | IUPHAR_ligand = 10910 | DrugBank_Ref = | DrugBank = DB00301 | ChemSpiderID_Ref = | ChemSpiderID = 20037 | KEGG_Ref = | KEGG = D04196 | ChEBI_Ref = | ChEBI = 5098 | ChEMBL_Ref = | ChEMBL = 222645 | NIAID_ChemDB = | PDB_ligand = | synonyms = BRL-2039

| IUPAC_name = (2S,5R,6R)-6-({[3-(2-chloro-5-fluorophenyl)-5-methylisoxazol-4-yl]carbonyl}amino)-3,3-dimethyl-7-oxo-4-thia-1-azabicyclo[3.2.0]heptane-2-carboxylic acid | C=19 | H=17 | Cl=1 | F=1 | N=3 | O=5 | S=1 | SMILES = O=C(O)[C@@H]3N4C(=O)C@@H[C@H]4SC3(C)C | StdInChI_Ref = | StdInChI = 1S/C19H17ClFN3O5S/c1-7-10(12(23-29-7)11-8(20)5-4-6-9(11)21)15(25)22-13-16(26)24-14(18(27)28)19(2,3)30-17(13)24/h4-6,13-14,17H,1-3H3,(H,22,25)(H,27,28)/t13-,14+,17-/m1/s1 | StdInChI_comment = | StdInChIKey_Ref = | StdInChIKey = UIOFUWFRIANQPC-JKIFEVAISA-N | density = | density_notes = | melting_point = | melting_high = | melting_notes = | boiling_point = | boiling_notes = | solubility = | sol_units = | specific_rotation =

Flucloxacillin, also known as floxacillin, is an antibiotic used to treat skin infections, external ear infections, infections of leg ulcers, diabetic foot infections, and infection of bone. It may be used together with other medications to treat pneumonia, and endocarditis. It is taken by mouth or given by injection into a vein or muscle.

Common side effects include an upset stomach. It appears to be safe during pregnancy and breastfeeding.

Flucloxacillin was patented in 1961.

Flucloxacillin is not available in the United States.

Medical uses

Flucloxacillin is an antibiotic used to treat lactational mastitis (drug of choice), skin infections, external ear infections, infections of leg ulcers, diabetic foot infections, and infection of bone.

Skin

Flucloxacillin is used for both staphylococcal and streptococcal skin infections. These include folliculitis, carbuncles, impetigo, ecthyma, cellulitis, erysipelas, necrotising fasciitis, and infections of skin conditions such as eczema, scabies, ulcers and acne. Due to the widespread belief that dual-therapy is needed to cover both Staphylococcus and Streptococcus in cellulitis, flucloxacillin is sometimes given with the addition of benzylpenicillin for more severe cellulitis. In the UK, using flucloxacillin alone is the first choice for treating cellulitis. Some other countries vary.

File:Pecho enrojecido.jpg|Infectious mastitis File:Impetigo2020.jpg|Impetigo File:Facial erysipelas.jpg|Erysipelas File:Folliculitis2.jpg|Folliculitis File:Cellulitis1.jpg|Cellulitis File:Carbuncle.jpg|Carbuncle

Wounds

Infections of leg ulcers can be treated with flucloxacillin. With diabetic foot infections the dose is adjusted according to whether the infection appears mild, moderate or severe.

Bone

Despite having a lower than optimum drug penetration into bone ratio of 10–20%, flucloxacillin appears effective in treating osteomyelitis.

Depending on local guidance it may be used in the treatment of infection of joints while waiting for culture results.

Other

It may be used in combination with other antibiotics to treat pneumonia and can be used to prevent infection before surgery, particularly heart, lung, or bone surgery. When used to treat endocarditis, in combination with other antibiotics or alone, the dose of flucloxacillin may need to exceed the usual dose.

Resistance

Despite flucloxacillin being insensitive to beta-lactamases, some organisms have developed resistance to it and other narrow-spectrum β-lactam antibiotics including methicillin. Such organisms include methicillin-resistant Staphylococcus aureus, which has developed resistance to flucloxacillin and other penicillins by having an altered penicillin-binding protein.

Side effects

Common side effects associated with the use of flucloxacillin include: diarrhoea, nausea, rash, urticaria, pain and inflammation at injection site, superinfection (including candidiasis), allergy, and transient increases in liver enzymes and bilirubin.

Rarely, in fewer than 1 in 1,000 people, cholestatic jaundice (also referred to as cholestatic hepatitis) has been associated with flucloxacillin therapy. It may appear as pale stool with dark urine, and yellowish eyes and skin. The reaction may occur up to several weeks after treatment has stopped, and takes weeks to resolve. The estimated incidence is one in 15,000 exposures, and is more frequent in people over the age of 55, females, and those with a treatment duration of longer than two weeks.

Flucloxacillin is contraindicated in those with a previous history of allergy to penicillins, cephalosporins, or carbapenems. It should also not be used in the eye, or administered to those with a history of cholestatic hepatitis associated with the use of dicloxacillin or flucloxacillin.

It should be used with caution in the elderly, patients with renal impairment where a reduced dose is required, and those with hepatic impairment, due to the risk of cholestatic hepatitis.

It should be taken on an empty stomach, as absorption is reduced when taken with food, though some studies suggest that this does not compromise flucloxacillin plasma concentrations in most circumstances.

Drug interactions

Flucloxacillin can reduce the excretion of methotrexate, potentially resulting in a risk of methotrexate toxicity. The level of flucloxacillin in the blood may rise in kidney failure and with the use of probenecid.

Mechanism of action

Main article: Beta-lactam antibiotic

Flucloxacillin is a narrow-spectrum antibiotic belonging to the penicillin group of antibiotics. It works by breaking down the bacterial cell wall.

Like other β-lactam antibiotics, flucloxacillin acts by inhibiting the synthesis of bacterial cell walls. It inhibits cross-linkage between the linear peptidoglycan polymer chains that make up a major component of the cell wall of Gram-positive bacteria.

Flucloxacillin is more acid-stable than many other penicillins and can be given orally, in addition to parenteral routes. However, like methicillin, it is less potent than benzylpenicillin against non-β-lactamase-producing Gram-positive bacteria.

Flucloxacillin has similar pharmacokinetics, antibacterial activity, and indications to dicloxacillin, and the two agents are considered interchangeable. It is reported to have higher, though rare, incidence of severe hepatic adverse effects than dicloxacillin, but a lower incidence of renal adverse effects.

Chemistry

Flucloxacillin is insensitive to beta-lactamase (also known as penicillinase) enzymes secreted by many penicillin-resistant bacteria. The presence of the isoxazolyl group on the side chain of the penicillin nucleus facilitates the β-lactamase resistance, since they are relatively intolerant of side chain steric hindrance. Thus, it is able to bind to penicillin-binding proteins and inhibit peptidoglycan crosslinking, but is not bound by or inactivated by β-lactamases.

History

Flucloxacillin was developed in the 1960s following an increase in penicillin-resistant (beta-lactamase producing) staphylococcal infections due to the widespread use of benzylpenicillin by 1960. All the natural penicillins and first semi-synthetic penicillins were destroyed by staphylococcal beta-lactamase, leading Beecham (later GlaxoSmithKline) to search for more stable antibiotics. By 1962, a series of similarly structured acid-stable penicillins (oxacillin, cloxacillin, dicloxacillin and flucloxacillin), with the potential for being taken by mouth, were developed. Flucloxacillin and dicloxacillin showed particular stability against the beta-lactamase enzyme of Staph. aureus and could withstand acid. Flucloxacillin was first marketed in Europe in the 1970s.

Available forms

Both the oral and intravenous preparations of flucloxacillin are inexpensive and are available as the sodium salt flucloxacillin sodium, in capsules (250 or 500 mg), oral suspensions (125 mg/5 ml or 250 mg/5 ml), and injections (powder for reconstitution, 250, 500, 1000 and 2000 mg per vial).

Flucloxacillin is not commonly used in the United States or Canada as of 2011, It is supplied under a variety of trade names including Floxapen, Flopen, Flubex, Flupen, Phylopen, and Staphylex.

Combination

Main article: Co-fluampicil

Flucloxacillin is combined with ampicillin in co-fluampicil.

File:Flucloxacillin powder for oral solution.jpg|Flucloxacillin powder for oral solution 125 mg/5ml, with measuring spoon File:Flucloxacillin preparations.jpg|Selection of Flucloxacillin preparations found in the UK File:Co-fluampicil capsules and container.jpg|Co-fluampicil: Flucloxacillin combined with ampicillin (UK)

References

References

  1. "Flucloxacillin".
  2. (13 September 2024). "Flucloxacillin Baxter (Baxter Healthcare Pty Ltd)".
  3. https://www.tga.gov.au/resources/prescription-medicines-registrations/eug-flucloxacillin-eugia-pharma-australia-pty-ltd {{Bare URL inline. (August 2025)
  4. [https://www.ema.europa.eu/documents/psusa/flucloxacillin-list-nationally-authorised-medicinal-products-psusa/00001402/202003_en.pdf List of nationally authorised medicinal products]. European Medicines Agency. November 2020
  5. (2015). "The Top 100 Drugs e-book: Clinical Pharmacology and Practical Prescribing". Churchill Livingstone; Elsevier.
  6. (September 2020 – March 2021). "[[British National Formulary". BMJ Group and the Pharmaceutical Press.
  7. (2005). "Methicillin-resistant Staphylococcus aureus (MRSA)".
  8. (2006). "Analogue-based Drug Discovery". Wiley-VCH.
  9. (26 October 2023). "Streptococcal skin infection – DermNet New Zealand".
  10. (2016). "Oxford Textbook of Fundamentals of Surgery". Oxford University Press.
  11. (May 2005). "Flucloxacillin alone or combined with benzylpenicillin to treat lower limb cellulitis: a randomised controlled trial". Emergency Medicine Journal.
  12. (2011). "Treatments for Skin of Color E-Book". Saunders Elsevier.
  13. (2009). "Evidence-Based Dermatology". Blackwell Publishing.
  14. (March 2018). "Diagnosis and management of cellulitis". Clinical Medicine.
  15. (1 January 2020). "Oral Flucloxacillin for Treating Osteomyelitis: A Narrative Review of Clinical Practice". Journal of Bone and Joint Infection.
  16. (April 2019). "Antibiotic penetration into bone and joints: An updated review". International Journal of Infectious Diseases.
  17. (May 1982). "Methicillin resistance in Staphylococcus aureus with particular reference to Victorian strains". The Medical Journal of Australia.
  18. (8 July 2025). "Flucloxacillin: antibiotic to treat infections".
  19. "New Zealand Consumer Medicine Information". medsafe.govt.nz.
  20. (2018). "In healthy volunteers, taking flucloxacillin with food does not compromise effective plasma concentrations in most circumstances". PLOS ONE.
  21. "Flucloxacillin sodium salt". PubChem at the National Institutes of Health.
  22. (2012). "LiverTox: Clinical and Research Information on Drug-Induced Liver Injury". National Institute of Diabetes and Digestive and Kidney Diseases.
  23. Rossi S, editor. [[Australian Medicines Handbook]] 2006. Adelaide: Australian Medicines Handbook; 2006.
  24. (2010). "Analogue-based Drug Discovery II". Wiley-VCH.
  25. (2012). "Antibiotic Discovery and Development".
  26. (2008). "Antimicrobial Drugs: Chronicle of a Twentieth Century Medical Triumph". [[Oxford University Press]].
  27. (November 1970). "Flucloxacillin, a new isoxazolyl penicillin, compared with oxacillin, cloxacillin, and dicloxacillin". British Medical Journal.

::callout[type=info title="Wikipedia Source"] This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page. ::

penicillinsenantiopure-drugshepatotoxinsisoxazoles2-chlorophenyl-compounds2-fluorophenyl-compounds