Makindo Medical Notes

⚠️ Avoid in patients with glandular fever (EBV), CMV infection, ALL/CLL as it can cause a characteristic rash.

📖 About

Always check the BNF link here.

• 💊 Amoxicillin – a broad-spectrum aminopenicillin.
• Better absorbed orally than ampicillin → higher bioavailability and fewer GI side effects.
• Often combined with clavulanic acid (as Co-amoxiclav) to overcome beta-lactamase resistance.

⚡ Mechanism of Action

• 🔪 Beta-lactam antibiotic – interferes with bacterial cell wall synthesis.
• Inhibits cross-linking of peptidoglycan in bacterial cell walls → cell lysis.
• Destroyed by beta-lactamase enzymes (unless combined with clavulanic acid).

🧬 Spectrum of Activity

• ✅ E. coli (some strains), Proteus mirabilis, Shigella, Salmonella.
• ✅ Haemophilus influenzae, some Enterococci.
• ❌ Not reliable against beta-lactamase–producing organisms or Pseudomonas.

🩺 Indications & Typical Adult Dosing

📚 Teaching Points

• Amoxicillin is first-line for many community infections in the UK (e.g. pneumonia, otitis, sinusitis).
• High doses (e.g. meningitis, endocarditis) are used for CNS penetration and synergy with aminoglycosides.
• Lower doses may suffice in mild ENT/skin infections, but stewardship principles apply.
• BNF and local antimicrobial guidelines should always be checked before prescribing.

🔄 Interactions

• ⬇️ May reduce efficacy of the oral contraceptive pill (OCP) – advise backup contraception.
• ⬆️ Probenecid increases amoxicillin levels by reducing renal clearance.
• ⬆️ Risk of methotrexate toxicity (reduced clearance).

⚠️ Cautions

• Allergy risk – always ask about penicillin history.
• Characteristic rash if given with glandular fever (EBV), CMV, ALL or CLL.
• Adjust dose in renal impairment.

🚫 Contraindications

• Known penicillin allergy.

💥 Side Effects

• 🫁 Hypersensitivity: rash, urticaria, angioedema, anaphylaxis.
• 🌡️ Red maculopapular rash – especially in EBV, CMV, or haematological malignancy.
• 🤢 GI upset: nausea, vomiting, diarrhoea.
• 💩 Antibiotic-associated colitis (rare).
• 🦠 Opportunistic infection: oral/vaginal candidiasis.
• Rare: interstitial nephritis, haemolytic anaemia, hepatitis.

📑 References

• BNF: Amoxicillin
• NICE Antimicrobial Prescribing Guidelines