Benzylpenicillin Sodium (Penicillin G)
📖 About
Always check the BNF link here.
- 💊 Benzylpenicillin (Penicillin G) – one of the oldest and most important beta-lactam antibiotics.
- ⚠️ Deactivated by beta-lactamase–producing bacteria.
- 🚫 Cannot be given orally (acid-labile, destroyed by gastric acid).
⚡ Mechanism of Action
- 🔪 Bactericidal: inhibits bacterial cell wall synthesis.
- Prevents formation of peptidoglycan cross-links → weakens cell wall → lysis.
🧬 Spectrum of Activity
- ✅ Streptococci, Pneumococci, Meningococci.
- ✅ Neisseria gonorrhoeae (though resistance now common).
- ✅ Treponema pallidum (syphilis – gold standard).
- ✅ Actinomyces israelii.
- ✅ Anaerobes of mouth/upper GI tract.
- ❌ Not effective against Bacteroides fragilis (lower bowel anaerobe).
🩺 Indications
- ENT & respiratory: throat infections, otitis media, pneumonia.
- Cardiac: infective endocarditis.
- CNS: meningitis, neurosyphilis, brain abscess.
- Genitourinary: syphilis, gonorrhoea.
- Other: actinomycosis, anthrax, gas gangrene, diphtheria, leptospirosis, Lyme disease.
💊 Dose Range (verify with BNF/datasheet)
| Indication | Dose | Frequency | Route |
|---|
| Acute infection | 600 mg – 1.2 g | 6-hourly | IM/IV |
| Endocarditis | 1.2 – 2.4 g | 4-hourly | IV |
| Anthrax | 2.4 g | 4-hourly | IV |
| Suspected meningitis (pre-hospital) | 1.2 g | Stat | IM/IV |
| Meningitis | 2.4 g | 4-hourly | IV |
🔄 Interactions
- ⬆️ Probenecid reduces renal excretion → raises serum levels (sometimes used therapeutically).
- ⬆️ Risk of methotrexate toxicity (reduced clearance).
⚠️ Cautions
- 🚨 Allergy – risk of hypersensitivity/anaphylaxis.
- 🧪 May cause false-positive urine dipstick for glucose.
- 📉 Adjust dose in renal impairment.
🚫 Contraindications
- Known penicillin allergy (consider erythromycin or doxycycline as alternatives).
💥 Side Effects
- 🫁 Allergic reactions: rash, urticaria, fever, angioedema, anaphylaxis.
- 🩺 Renal: interstitial nephritis.
- 🩸 Haematological: haemolytic anaemia, leucopenia, thrombocytopenia.
- 💩 GI: antibiotic-associated colitis (rare, but important).
- 🧠 High IV doses: neurotoxicity, convulsions.
📑 References
