Flucloxacillin
A narrow-spectrum penicillin that resists staphylococcal penicillinase, used for staphylococcal skin, soft tissue, bone and heart infections.
Also called floxacillin (US name).
Drug card
- Class
- Penicillin
- How it works
- Blocking the enzymes that cross-link the bacterial cell wall, so bacteria burst
- Used for
- Cellulitis, impetigo and infected wounds
- Bone infections (osteomyelitis)
- Staphylococcal endocarditis
- Ear infections (otitis externa and media)
- Known for
- Cholestatic jaundice, up to 2 months after stopping
- Its name
- -cillin means a penicillin
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does flucloxacillin work?
Flucloxacillin is an isoxazolyl penicillin. Staphylococcal beta-lactamase (penicillinase) does not inactivate it, so it kills penicillinase-producing Staphylococcus aureus as well as streptococci, though it is weaker than benzylpenicillin against streptococci. It does not work against methicillin-resistant staphylococci (MRSA) or Enterococcus faecalis.
Like other penicillins: Penicillins carry a beta-lactam ring that binds and inactivates penicillin-binding proteins (PBPs), the enzymes that cross-link peptidoglycan in the bacterial cell wall. The weakened wall gives way and dividing bacteria burst, so penicillins are bactericidal. Bacteria resist them by making beta-lactamases (penicillinases) or by changing their PBPs.
Uses
What is flucloxacillin used for?
- Cellulitis, impetigo and infected wounds
- Bone infections (osteomyelitis)
- Staphylococcal endocarditis
- Ear infections (otitis externa and media)
- Preventing infection in major surgery
Side effects
Side effects of flucloxacillin
- Cholestatic jaundice, up to 2 months after stoppingKnown forSerious
- Hepatitis (liver inflammation)Serious
- Nausea
- Diarrhea
- Indigestion and bloating
- Allergic reactions, including anaphylaxisSerious
- C. difficile colitisSerious
- Severe skin reactions, including AGEPSerious
- Low potassium, sometimes severeSerious
- Metabolic acidosis when taken with paracetamolSerious
- Interstitial nephritis (kidney injury)Serious
- Phlebitis after intravenous infusion
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- Never give it again after flucloxacillin jaundice; age over 50, liver disease and courses longer than 2 weeks raise the liver risk.
- With paracetamol it can cause high anion gap metabolic acidosis, mainly in sepsis, malnutrition or severe kidney impairment.
- High doses can lower potassium, so potassium is checked, especially with diuretics that also lower it.
Good to know: It has no US label. Like oxacillin, cloxacillin and dicloxacillin it is an isoxazolyl penicillin, and like them it does not work against MRSA.
Remember it
A way to remember it
Penicillins jam the wall builders: only growing bacteria, busy laying new wall, are killed.
The penicillin-binding proteins are the enzymes that link peptidoglycan strands into a firm wall. Penicillins block them, so bacteria die while they multiply; a drug that halts growth, such as a tetracycline, can blunt this effect.
Written for biofideX
Its name
-cillin means penicillin
Marks penicillins (6-aminopenicillanic acid derivatives), including benzylpenicillin. Beta-lactamase inhibitors given with them keep their own names: clavulanic acid, tazobactam.
- Every drug name stem
Its class
Penicillins
Other penicillins with a card:
Easily mixed up with cephalosporins, carbapenems and glycopeptides.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- Flucloxacillin 500 mg capsules, hard: SmPC (emc)
- Flucloxacillin 1g powder for solution for injection or infusion: SmPC (emc)
- Flucloxacillin (NCI Thesaurus)
- About flucloxacillin (NHS)
- Side effects of flucloxacillin (NHS)
For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.
Antibiotics: the cell wall
Flucloxacillin is one of 12 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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