Amoxicillin + clavulanic acid !

Amoxicillin shielded by clavulanic acid, which blocks β-lactamases; an oral antibiotic for otitis, sinusitis, pneumonia and skin infections.

Updated 2026-11-01

Class: Beta-lactams
Enzyme: Bacterial PBPs (amoxicillin) and β-lactamases (clavulanic acid)
ATC code: J01CR02
WHO Model List of Essential Medicines

Also called: co-amoxiclav, amoxicillin–clavulanate

Bacterial PBPs (amoxicillin) and β-lactamases (clavulanic acid)Amoxicillin + clavulanic acid

The figure shows clavulanic acid in the active site of the extended-spectrum β-lactamase TLA-1 (S70G mutant, without the catalytic serine, so the molecule stays intact); amoxicillin acts on the PBPs as on its own page.

Target in 3D: Bacterial PBPs (amoxicillin) and β-lactamases (clavulanic acid). PDB structure 6PQ8 (RCSB PDB, public domain). View the structure at RCSB PDB

Mechanism of action

Amoxicillin acylates the penicillin-binding proteins (PBPs) and stops peptidoglycan cross-linking. Many bacteria (Haemophilus influenzae, Moraxella catarrhalis, Staphylococcus aureus, anaerobes, enteric gram-negatives) destroy it with β-lactamases. Clavulanic acid has almost no antibacterial action of its own but is a 'suicide' inhibitor: the β-lactamase opens it and is irreversibly inactivated, so amoxicillin reaches its PBPs intact.

The bacterium secretes β-lactamase to defend itself
Clavulanic acid binds the β-lactamase and inactivates it
Amoxicillin, now protected, acylates the PBPs
Without cross-links the wall gives way and the bacterium lyses

Pharmacokinetics

Absorption: Both are well absorbed by mouth; taking it at the start of a meal improves clavulanate absorption and stomach tolerance.
Elimination: Amoxicillin leaves mostly unchanged in the urine; clavulanate by the urine and by metabolism.
Half-life: About 1.3 hours for amoxicillin and 1 hour for clavulanic acid.

Indications

Acute otitis media due to β-lactamase-producing bacteria. Acute otitis media →
Acute bacterial sinusitis. Acute rhinosinusitis →
Lower respiratory tract infections such as community-acquired pneumonia. Community-acquired pneumonia →
Skin and soft-tissue infections. Cellulitis of the leg →
Urinary tract infections by susceptible strains. Urinary tract infection (acute cystitis) →

Adverse effects

Common

Diarrhoea (more often than with amoxicillin alone), nausea and vomiting
Rash; very common if the patient has infectious mononucleosis
Vaginal or oral candidiasis

Contraindications

History of a serious hypersensitivity reaction (anaphylaxis, Stevens–Johnson syndrome) to any penicillin or other β-lactam
Previous cholestatic jaundice or liver dysfunction linked to amoxicillin + clavulanic acid

Key interactions

Probenecid: Reduces tubular secretion: higher and longer-lasting β-lactam levels.
Allopurinol: Raises the rate of rash with aminopenicillins.
Oral anticoagulants (warfarin): May prolong the prothrombin time; the INR is monitored.

What is monitored

Clinical response in the first days
Liver tests if there is prior liver disease or jaundice, dark urine or itching appear
INR if the patient takes warfarin

Administration and safety

Oral; given at the start of a meal to improve stomach tolerance.
Presentations are not interchangeable: the clavulanate ratio differs, and two tablets do not equal one stronger tablet.
Do not confuse it with plain amoxicillin: the names look alike and the spectrum is not the same.

Nursing care

Before the first dose: ask about allergy to penicillins, cephalosporins and other β-lactams, and what the reaction was.
After the first dose, watch for hives, wheeze, low blood pressure or swelling of lips and tongue, with anaphylaxis equipment at hand.
Watch for jaundice, dark urine, pale stools or itching, also after the course ends.
Teach the patient to report watery or bloody diarrhoea, even weeks after the course ends.
Stress completing the prescribed course even if symptoms improve.

Pregnancy and breastfeeding

Decades of use have not shown more birth defects; in preterm prelabour rupture of membranes it has been linked to more neonatal necrotising enterocolitis.

Test yourself

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

Why is clavulanic acid called a 'suicide' inhibitor?

Because the β-lactamase takes it as a substrate, opens its ring and remains irreversibly bound to it: the enzyme inactivates itself while trying to destroy it.

Which serious adverse effect rules out using amoxicillin + clavulanic acid again?

Cholestatic jaundice or liver dysfunction linked to a previous course of the combination.

What extra spectrum does clavulanate add to amoxicillin?

It covers β-lactamase producers such as H. influenzae, M. catarrhalis, methicillin-susceptible S. aureus and many anaerobes.

Does clavulanate help against methicillin-resistant Staphylococcus aureus (MRSA)?

No. MRSA resists through PBP2a, a low-affinity PBP, not through a β-lactamase; blocking the β-lactamase does not fix that.

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

Sources: Amoxicillin and Clavulanic Acid: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); DailyMed - AMOXICILLIN AND CLAVULANATE POTASSIUM tablet, film coated (DailyMed (U.S. National Library of Medicine), 2026); RCSB PDB - 6PQ8: Crystal structure of TLA-1 S70G extended spectrum Beta-lactamase in complex with clavulanic acid (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.