Flucloxacillin: Mechanism of Action
Flucloxacillin is a penicillin antibiotic used to treat a wide range of bacterial infections including respiratory, skin, and urinary tract infections.
Penicillins inhibit bacterial cell wall synthesis by binding penicillin-binding proteins, causing osmotic instability and bacteriolysis.
How It Works
Penicillins are β-lactam antibiotics that inhibit the final transpeptidation step of bacterial peptidoglycan synthesis. The β-lactam ring mimics the D-Ala-D-Ala dipeptide substrate of penicillin-binding proteins (PBPs — transpeptidases and carboxypeptidases), forming a covalent acyl-enzyme complex. Inhibition of PBPs prevents cell wall cross-linking, leading to osmotic instability and bacterial lysis. Bactericidal activity is time-dependent (T>MIC). Beta-lactamase-producing bacteria inactivate penicillins by hydrolysing the β-lactam ring; combination with clavulanate restores activity against these resistant strains.
Receptor / Target Profile
- •PBP1a/1b (transpeptidase) — primary target causing rapid cell lysis
- •PBP2 — maintains cell shape; binding leads to spheroplast formation
- •PBP3 — septum formation inhibition; filamentation
- •Beta-lactamase enzymes — site of resistance; overcome by clavulanate, sulbactam, tazobactam co-administration
Pharmacokinetics
Onset of Action
Peak serum levels 1–2 hours (oral); antibiotic effect dependent on time above MIC (T>MIC ≥40%)
Half-Life (t½)
Amoxicillin: ~1 hour; Ampicillin: ~1.5 hours; Benzylpenicillin: ~30 minutes (requires frequent dosing); Flucloxacillin: ~0.75 hours
Bactericidal activity is time-dependent — efficacy correlates with duration of time serum concentration exceeds MIC (T>MIC ≥40% of dosing interval). Primarily renally eliminated unchanged. CNS penetration poor normally; adequate in meningitis (inflamed BBB). IgE-mediated allergy in 1–10% reported; cross-reactivity with cephalosporins ~1–2%.
Conditions Treated with Flucloxacillin
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