Makindo Medical Notes

📖 About

Always check the BNF or equivalent for prescribing advice.

• 💉 Penicillin was the first antibiotic, discovered by Alexander Fleming in 1928. He observed that the mould Penicillium notatum inhibited growth of Staphylococcus aureus in culture.
• ⚗️ Its clinical development was advanced in the 1940s, revolutionising treatment of bacterial infections.
• 🌍 Remains a cornerstone of antimicrobial therapy despite increasing resistance.

⚡ Mechanism of Action

• 🔪 Bactericidal: inhibits bacterial cell wall synthesis.
• Blocks formation of peptidoglycan cross-links in the bacterial cell wall.
• Contain a beta-lactam ring, which is vulnerable to hydrolysis by bacterial beta-lactamases.

📝 Notes

• 💊 Clavulanic acid is a beta-lactamase inhibitor – protects penicillins against resistant organisms (e.g. co-amoxiclav).
• 📊 Different classes: narrow-spectrum (benzylpenicillin), broad-spectrum (ampicillin, amoxicillin), anti-staphylococcal (flucloxacillin), and anti-pseudomonal (piperacillin-tazobactam).

🩺 Indications

• Refer to the BNF for up-to-date prescribing indications (e.g. pneumonia, cellulitis, endocarditis, syphilis).

🔄 Interactions

• 💊 Ampicillin/amoxicillin may reduce efficacy of the oral contraceptive pill (OCP) (advise extra precautions).
• ⬆️ Probenecid inhibits renal excretion → doubles serum penicillin levels (sometimes used therapeutically).
• ⬆️ Increased methotrexate toxicity (reduced clearance).

⚠️ Cautions

• Consult the BNF for detailed cautionary advice.
• 📉 Dose adjustment required in renal impairment.
• 🧪 Beware in patients with a history of severe allergy or asthma (higher risk of hypersensitivity).

🚽 Excretion

• Undergo enterohepatic recirculation and renal clearance.
• Primarily excreted by active tubular secretion in the kidneys.
• 💊 Probenecid blocks this process → prolongs serum half-life.

🚫 Contraindications

• ⚠️ Known hypersensitivity to penicillins (risk of anaphylaxis).
• Refer to the BNF for full list.

💥 Side Effects

• 🫁 Acute anaphylaxis: rare (~5 per 10,000 patients) but potentially fatal.
• 🌡️ Rashes – including maculopapular rash with ampicillin/amoxicillin in EBV or CLL.
• 🩸 Haematological: haemolytic anaemia, thrombocytopenia, neutropenia.
• 🩺 Renal: interstitial nephritis.
• 🧠 Neurotoxicity: convulsions at high IV/intrathecal doses.
• 🔄 Cross-sensitivity with cephalosporins (~10%).