Makindo Medical Notes

⚠️ Not suitable for serious or life-threatening infections because of unpredictable pharmacokinetics and lower potency compared to benzylpenicillin.

📖 About

Always check the BNF link here.

• 💊 Phenoxymethylpenicillin (Penicillin V) is similar to benzylpenicillin but is acid-stable and can be taken orally.
• ⬇️ Less active than benzylpenicillin → not recommended for severe infections.
• 🌍 Commonly used for streptococcal throat infections, prophylaxis in post-splenectomy patients, and rheumatic fever prevention.

⚡ Mechanism of Action

• 🔪 Bactericidal: interferes with bacterial cell wall synthesis.
• Blocks formation of peptidoglycan cross-links, weakening the cell wall and causing lysis.

🧬 Spectrum of Activity

• ✅ Streptococci, Pneumococci, Meningococci.
• ✅ Treponema pallidum, Actinomyces israelii.
• ✅ Anaerobes of mouth/upper GI tract.
• ❌ Not reliable against gonococci or Bacteroides fragilis (lower bowel anaerobes).

🩺 Indications

• 📌 Prophylaxis post-splenectomy or after rheumatic fever.
• 👂 ENT infections: otitis media, tonsillitis, pharyngitis.
• 🦠 Skin/soft tissue infections: cellulitis, erysipelas.
• Streptococcal throat infections (Group A Strep).

💊 Dosing – Phenoxymethylpenicillin (verify with BNF/datasheet)

🔄 Interactions

• See BNF – interactions are generally minimal but check carefully.
• ⬆️ Probenecid may increase serum levels (reduces renal clearance).
• May reduce efficacy of the oral contraceptive pill (OCP).

⚠️ Cautions

• 🚨 Penicillin allergy (cross-reactivity with cephalosporins ~10%).
• 📉 Use with caution in severe renal impairment (dose adjustment may be needed).
• Long-term prophylaxis should be reviewed regularly to reduce resistance risk.

🚫 Contraindications

• Do not use for meningococcal or gonococcal infections.
• Not recommended for severe/systemic infections – efficacy unpredictable.

💥 Side Effects

• 🫁 Allergic reactions: anaphylaxis, urticaria, rash, angioedema, fever.
• 🩸 Haematological: haemolytic anaemia, leucopenia, thrombocytopenia.
• 🩺 Renal: interstitial nephritis.
• 💩 Gastrointestinal: nausea, diarrhoea, antibiotic-associated colitis (rare).
• Rare neurotoxicity (e.g. seizures) with very high doses.

📑 References

• BNF: Phenoxymethylpenicillin
• NICE guidance: Antibiotics for sore throat