Reviewed by MedNext Clinical Team
Co-amoxiclav (amoxicillin-clavulanate) combines the broad-spectrum aminopenicillin amoxicillin with clavulanic acid, a beta-lactamase inhibitor. This combination extends the spectrum of amoxicillin to include beta-lactamase-producing organisms that would otherwise be resistant, making co-amoxiclav one of the most widely prescribed antibiotics in community and hospital settings. However, its use carries a risk of cholestatic hepatotoxicity that prescribers must understand [1].
How Beta-Lactamase Inhibition Works
Many clinically important bacteria — including Staphylococcus aureus (MSSA), Haemophilus influenzae, Moraxella catarrhalis, Escherichia coli, Klebsiella spp., and anaerobes — produce beta-lactamase enzymes that cleave the beta-lactam ring of penicillins, rendering them inactive. Clavulanic acid acts as a "suicide inhibitor" — it binds irreversibly to beta-lactamase, sacrificing itself to protect amoxicillin and allowing it to reach its target (penicillin-binding proteins) and inhibit bacterial cell wall synthesis.
When to Choose Co-amoxiclav Over Amoxicillin
Amoxicillin alone remains appropriate for many community infections (streptococcal tonsillitis, mild community-acquired pneumonia in low-risk patients, H. pylori eradication). Co-amoxiclav is indicated when beta-lactamase-producing organisms are likely or confirmed:
- Bite wounds: Human and animal bite infections involve mixed aerobic/anaerobic flora including Pasteurella multocida (cat/dog bites) and Eikenella corrodens (human bites) — co-amoxiclav is first-line for prophylaxis and treatment
- Dental infections: Odontogenic abscesses with mixed aerobic-anaerobic flora not responding to amoxicillin alone
- Complicated UTI and pyelonephritis: When culture data supports susceptibility
- Sinusitis, otitis media: Step-up treatment when first-line agents have failed
- Hospital-acquired and aspiration pneumonia
- Diabetic foot infections: Mixed polymicrobial coverage [1]
Dosing
Standard oral dose: 625 mg (500/125 mg) three times daily, or 375 mg (250/125 mg) three times daily for milder infections. Co-amoxiclav tablets are available in different strength ratios — always check the amoxicillin and clavulanate content separately. Intravenous 1.2 g (1000/200 mg) is used in hospitalised patients, typically every 8 hours.
Hepatotoxicity Risk
Co-amoxiclav is one of the most common drug causes of drug-induced liver injury (DILI) in the UK and Europe. The pattern is typically cholestatic or mixed hepatocellular-cholestatic, and is thought to be primarily due to clavulanate rather than amoxicillin. Onset is usually 1–6 weeks after starting treatment and may be delayed until after the course has been completed. The risk increases with age, male sex, longer courses, and repeated courses. Jaundice usually resolves after stopping the drug, but severe cases can result in prolonged cholestasis [1].
Patients should be counselled to report jaundice, dark urine, or pale stools promptly. Co-amoxiclav should generally be avoided in patients with a history of cholestatic jaundice or hepatic dysfunction following previous use.
References
- Salvo F, De Sarro A, Caputi AP, Polimeni G. Amoxicillin and amoxicillin plus clavulanate: a safety review. Expert Opin Drug Saf. 2007;6(5):645-654.