Amoxicillin vs Co-amoxiclav
Clinical Comparison
Clinical Context
Amoxicillin is the first-line aminopenicillin for most community infections. Co-amoxiclav adds clavulanic acid to overcome beta-lactamase resistance, but should be reserved for infections where resistant organisms are likely or the infection is more severe, to support antimicrobial stewardship.
Drug Profiles
Amoxicillin
Aminopenicillin (beta-lactam antibiotic)
Mechanism
Inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), preventing peptidoglycan cross-linking
Indications
- Community-acquired pneumonia
- Acute otitis media
- Urinary tract infections (uncomplicated)
- H. pylori eradication
- Dental abscess
- Streptococcal pharyngitis
Common Doses
250-500 mg TDS or 1 g TDS for severe infections
Route
Oral, IV
Onset & Duration
Onset 1-2 hours oral; half-life 1 hour
Co-amoxiclav
Aminopenicillin + beta-lactamase inhibitor
Mechanism
Amoxicillin inhibits cell wall synthesis; clavulanic acid irreversibly inhibits bacterial beta-lactamases, restoring amoxicillin activity against resistant organisms
Indications
- UTIs (complicated)
- Animal bites
- Dental infections (severe)
- Intra-abdominal infections
- Lower respiratory tract infections when amoxicillin-resistant organisms suspected
- Diabetic foot infections
Common Doses
375 mg (250/125) or 625 mg (500/125) TDS; IV 1.2 g TDS
Route
Oral, IV
Onset & Duration
Onset 1-2 hours oral; half-life ~1 hour
Key Differences
| Category | Amoxicillin | Co-amoxiclav |
|---|---|---|
| Spectrum | Narrow — many organisms develop resistance via beta-lactamase | Broader — clavulanate restores activity against beta-lactamase producers |
| GI side effects | Mild diarrhoea | More diarrhoea and GI upset (clavulanate effect) |
| Liver toxicity | Very rare hepatotoxicity | Risk of cholestatic jaundice (clavulanate-related) |
| Bite wounds | Not adequate alone for animal/human bites | First-line for bite wound prophylaxis and treatment |
| Antimicrobial stewardship | Preferred to minimise resistance pressure | Reserve for cases with confirmed or likely resistance |
| C. difficile risk | Lower risk | Higher risk due to broader spectrum |
Spectrum
Narrow — many organisms develop resistance via beta-lactamase
Broader — clavulanate restores activity against beta-lactamase producers
GI side effects
Mild diarrhoea
More diarrhoea and GI upset (clavulanate effect)
Liver toxicity
Very rare hepatotoxicity
Risk of cholestatic jaundice (clavulanate-related)
Bite wounds
Not adequate alone for animal/human bites
First-line for bite wound prophylaxis and treatment
Antimicrobial stewardship
Preferred to minimise resistance pressure
Reserve for cases with confirmed or likely resistance
C. difficile risk
Lower risk
Higher risk due to broader spectrum
Key Advantages
Amoxicillin
- Narrow spectrum — less disruption to gut flora
- Very well tolerated
- Safe in pregnancy
- First-line for many community infections per NICE
- Cheap and widely available
Co-amoxiclav
- Active against beta-lactamase producing organisms (S. aureus, H. influenzae, E. coli)
- Broader gram-negative and anaerobic cover
- Reliable for bite wounds and polymicrobial infections
- IV formulation widely used in hospitals
Key Cautions
Amoxicillin
- Inactive against beta-lactamase producing organisms
- Amoxicillin rash (non-allergic) in EBV infection
- True penicillin allergy — anaphylaxis risk
- Diarrhoea common
- Check for penicillin allergy before prescribing
Co-amoxiclav
- Higher rate of diarrhoea and GI upset than amoxicillin alone
- Cholestatic jaundice risk (clavulanate-associated, usually reversible)
- More antibiotic-associated C. difficile risk
- Avoid if mononucleosis suspected
- Reserve for when broader spectrum genuinely needed
Clinical Verdict
Start with amoxicillin for uncomplicated community infections (pneumonia, otitis media, UTI). Step up to co-amoxiclav for bite wounds, complicated UTIs, severe dental infections, or when beta-lactamase resistance is suspected.
Medical Disclaimer: This comparison is for educational purposes only and is not a substitute for professional medical advice. Always consult a qualified healthcare professional before making prescribing decisions. Verify all drug information with current clinical guidelines (BNF, NICE, SmPCs).
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