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Flucloxacillin

Beta-lactamase-resistant penicillin

ATC code: J01CF05

Updated · Methodology

Indications

How to read tiers A–F
  • AStrong evidence – first or second line in international guidelines
  • BRecommended in selected cases
  • CStudy data contradict each other
  • DBenefit not proven, no documented harm
  • FDocumented harm, or risk without benefit

Mechanism of action

Narrow-spectrum isoxazolyl penicillin resistant to staphylococcal beta-lactamase. Bactericidal against MSSA, Streptococcus pyogenes, Streptococcus pneumoniae. Not active against MRSA. Bioavailability 50–70%, better on empty stomach.

Safety

Contraindications

  • Anaphylaxis to penicillins
  • History of flucloxacillin-induced hepatotoxicity

Serious adverse effects

  • Cholestatic hepatitis (1 per 100,000, often 1–9 weeks after start)
  • Anaphylaxis
  • C. difficile colitis

Common adverse effects

  • Nausea
  • Diarrhea
  • Skin rash

Pregnancy: can you take Flucloxacillin?

Safe in pregnancy.

Breastfeeding: can you take Flucloxacillin?

Hale L1 · Compatible

Compatible. Hale L1. RID about 0.3%, minimal infant exposure.

RID, infant dose via milk
0.3%
Maternal half-life
1 h
Maternal peak time
1 h
Peak milk concentration
0.3 mg/L
Milk-to-plasma ratio
0.03
Calculate RIDSafe feeding windowFull profile on NIH LactMed ↗

Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.

Practical notes

Timing and administration

Take on empty stomach 1 hour before or 2 hours after meals – food reduces bioavailability by 50%. Full course 10–14 days.
Label mentions3 mentions

Verbatim lines from the interaction sections, in the language of the label

From other drugs’ labels

  • MajorVoriconazole
    «Antibióticos: Si no se puede evitar la administraci ó n concomitante de voriconazol con flucloxacilina, se debe vigilar la posible p é rdida de eficacia de voriconazol (p. ej., mediante la…»

    AEMPS, section 4.5 · Open on CIMA

  • ModerateParacetamol
    «Se debe tener precaución cuando se utiliza paracetamol de forma concomitante con flucloxacilina, ya que la administración concurrente se ha asociado con acidosis metabólica con desequilibrio aniónico…»

    AEMPS, section 4.5 · Open on CIMA

  • Tacrolimus
    «Recomendaciones relativas a la a dministración simultánea: Inductores moderados del CYP3A4: metamizol, fenobarbital, isoniazida, rifabutina, efavirenz, etravirina, nevirapina; inductores débiles del…»

    AEMPS, section 4.5 · Open on CIMA

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Frequently asked

What is Flucloxacillin used for?

Flucloxacillin is evaluated for the following indications with varying evidence strength: Lactational mastitis (evidence tier A). See the full indication matrix with dosing and citations above on this page.

What are the side effects of Flucloxacillin?

Common side effects of Flucloxacillin (≥ 1 in 100): Nausea, Diarrhea, Skin rash. See the Safety section for uncommon and serious reactions.

Is Flucloxacillin safe during pregnancy?

Safe in pregnancy.

Is Flucloxacillin compatible with breastfeeding?

Compatible. Hale L1. RID about 0.3%, minimal infant exposure.

Who should not take Flucloxacillin?

Flucloxacillin is contraindicated in: Anaphylaxis to penicillins; History of flucloxacillin-induced hepatotoxicity. Full list in the Safety section.

Other drugs in this group

Fosfomycin, Gentamicin, Levofloxacin, Linezolid, Meropenem, Amoxicillin + Clavulanic Acid, Ceftriaxone, Clindamycin