Amoxicillin: Mechanism of Action
Amoxicillin is a penicillin antibiotic used to treat a wide range of bacterial infections including respiratory, skin, and urinary tract infections.
Amoxicillin is a broad-spectrum aminopenicillin with improved gram-negative coverage, acid stability, and near-complete oral absorption.
How It Works
Amoxicillin is an aminopenicillin whose para-aminophenylglycine side chain enhances outer membrane permeability in gram-negative bacteria (E. coli, H. influenzae, H. pylori, Salmonella) while retaining gram-positive coverage. Its acid stability and ~80% oral bioavailability (vs ~40% for ampicillin) makes it the preferred oral aminopenicillin. Amoxicillin-clavulanate (co-amoxiclav) adds a beta-lactamase inhibitor restoring activity against resistant H. influenzae, E. coli, Klebsiella, and MSSA. Mechanism remains β-lactam ring–mediated PBP inhibition and cell wall synthesis disruption.
Receptor / Target Profile
- •PBP1a/1b — bactericidal cell lysis
- •PBP2 — spheroplast formation
- •PBP3 — filamentation
- •Class A beta-lactamase — irreversibly inhibited by clavulanate (when co-formulated)
- •H. pylori PBPs — component of H. pylori triple/quadruple eradication therapy
Pharmacokinetics
Onset of Action
Peak serum concentration 1–2 hours; clinical response within hours for susceptible infections
Half-Life (t½)
~1 hour (extended in renal failure: dose-adjusted for eGFR <30)
Oral bioavailability ~80%; food does not significantly affect absorption. Primarily renal elimination (~80% unchanged). Adequate penetration in middle ear, lung, urinary tract, CSF (inflamed meninges).
Conditions Treated with Amoxicillin
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