[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Beta-lactams](https://durgical.com/en/pharmacology/classes/beta-lactams/) › Flucloxacillin

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# Flucloxacillin

A penicillinase-resistant penicillin, oral or injected, for staphylococcal skin, wound and bone infections; it rarely injures the liver.

Updated 2026-11-01

- Class: [Beta-lactams](https://durgical.com/en/pharmacology/classes/beta-lactams/)
- Enzyme: Penicillin-binding proteins (bacterial transpeptidases)
- ATC code: J01CF05

✂**Penicillin-binding proteins (bacterial transpeptidases)**Flucloxacillin

ⓘ The figure shows oxacillin, an isoxazolyl penicillin of the same group, in Staphylococcus aureus PBP1; no structure of this drug bound to a PBP has been published.

**Target in 3D:** Penicillin-binding proteins (bacterial transpeptidases). PDB structure 8VBU (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/8VBU) · Drag to rotate · pinch to zoom

## Mechanism of action

Flucloxacillin is an isoxazolyl penicillin, a relative of cloxacillin. It belongs to the penicillins resistant to staphylococcal β-lactamase: its bulky side chain keeps penicillinase from opening the β-lactam ring, so it acylates the PBPs of penicillinase-producing staphylococci. It does not work against MRSA, whose PBP2a has low affinity for β-lactams. Its hypersensitivity liver injury has been linked to the HLA-B*57:01 allele.

- Staphylococcal penicillinase cannot open its ring
- Acylates the staphylococcal PBPs
- Peptidoglycan cross-linking stops
- The staphylococcus lyses

## Pharmacokinetics

**Absorption**
Oral or injected; the oral form is taken on an empty stomach.

## Indications

- Skin and wound infections. [Cellulitis of the leg →](https://durgical.com/en/conditions/cellulitis-of-the-leg/)
- Bone infections (osteomyelitis). [Osteomyelitis →](https://durgical.com/en/conditions/osteomyelitis/)
- Ear infections.

## Adverse effects

### Common

- Nausea, vomiting, diarrhoea
- Bloating and indigestion

### Serious (rare, important)

- Anaphylaxis
- Liver injury with jaundice, which may appear up to weeks after finishing
- Severe blistering skin reactions
- Clostridioides difficile diarrhoea, from mild to severe colitis

## Contraindications

- History of a hypersensitivity reaction to any penicillin
- Liver or kidney disease: needs assessment before use

## Key interactions

**Methotrexate**
May raise its toxicity.

**Warfarin**
May alter the INR; it is monitored.

**Probenecid**
Reduces tubular secretion: higher and longer-lasting β-lactam levels.

**Oral typhoid vaccine**
Flucloxacillin can make it less effective.

## What is monitored

- Signs of liver injury: jaundice, dark urine, pale stools
- Liver function in patients with prior liver disease

## Administration and safety

- The oral form is taken at least one hour before eating or two hours after.
- Do not confuse flucloxacillin with cloxacillin or dicloxacillin.

## Nursing care

- Before the first dose: ask about allergy to penicillins, cephalosporins and other β-lactams, and what the reaction was.
- Teach the patient to recognise jaundice, dark urine or pale stools, also up to two months afterwards.
- Ask about prior liver or kidney disease.
- Teach the patient to report watery or bloody diarrhoea, even weeks after the course ends.

## Pregnancy and breastfeeding

It can be used in pregnancy and breastfeeding; little passes into breast milk.

## Memory aid

'FLUcloxacillin flows to the liver': good for skin staphylococci, but its hallmark is delayed cholestasis (and HLA-B*57:01).

## Test yourself

Think of the answer, then tap the question to see it.

## Which serious adverse effect characterises flucloxacillin?

Liver injury with jaundice, which may appear up to weeks after the course ends.

## Which HLA allele has been linked to flucloxacillin liver toxicity?

HLA-B*57:01, the same allele linked to abacavir hypersensitivity.

## Does flucloxacillin work for MRSA?

No; like the other isoxazolyl penicillins, it cannot overcome PBP2a.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/flucloxacillin/)

## Related drugs

- [Cloxacillin](https://durgical.com/en/pharmacology/cloxacillin/)
- [Dicloxacillin](https://durgical.com/en/pharmacology/dicloxacillin/)
- [Amoxicillin + clavulanic acid](https://durgical.com/en/pharmacology/amoxicillin-clavulanic-acid/)

## Related conditions

- [Cellulitis of the leg](https://durgical.com/en/conditions/cellulitis-of-the-leg/)
- [Osteomyelitis](https://durgical.com/en/conditions/osteomyelitis/)

[← Back to the class: Beta-lactams](https://durgical.com/en/pharmacology/classes/beta-lactams/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [Flucloxacillin: an antibiotic medicine to treat infections - NHS](https://www.nhs.uk/medicines/flucloxacillin/) (NHS (National Health Service, UK), 2025); Farmacología básica y clínica (Katzung), cap. 5 (McGraw Hill, 2025); [RCSB PDB - 8VBU: Structure of the monofunctional Staphylococcus aureus PBP1 in its beta-lactam (Oxacillin) inhibited form](https://www.rcsb.org/structure/8VBU) (RCSB Protein Data Bank, 2026); Farmacología básica y clínica (Katzung), cap. 43 (McGraw Hill, 2025).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/pharmacology/flucloxacillin/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/flucloxacillin/