Makindo Medical Notes

⚠️ Key safety note: Clarithromycin is a potent CYP3A4 inhibitor. Toxicity may occur with drugs such as theophylline, simvastatin, ciclosporin, colchicine, and sildenafil.

📖 About

Always check the BNF link here.

• 💊 Macrolide antibiotic, often preferred to erythromycin due to fewer GI side effects.
• 💷 More expensive than erythromycin.
• 🧪 Key role in triple therapy for Helicobacter pylori eradication.

⚡ Mechanism of Action

• Binds to the 50S ribosomal subunit, inhibiting bacterial protein synthesis.
• Usually bacteriostatic but can be bactericidal at high concentrations.

🧬 Properties

• ✅ Penetrates most tissues (except CSF).
• ⏱️ Half-life ~6 hours → typically dosed BD.
• ⚠️ 14-lactone macrolide ring → inhibits CYP3A4, leading to significant drug–drug interactions.

🩺 Indications

• 🌬️ Community-acquired pneumonia (CAP).
• 🦠 Atypical pneumonias – Mycoplasma, Chlamydophila, Legionella.
• 🤢 Alternative to erythromycin in respiratory infections.
• 🧪 Triple therapy for Helicobacter pylori (with amoxicillin + PPI).
• ENT/skin/soft tissue infections in penicillin-allergic patients.

💊 Dosing – Clarithromycin (verify with BNF/datasheet)

🔄 Interactions

• ⬆️ Levels of theophylline, carbamazepine, ciclosporin, colchicine, clozapine.
• ⬆️ Toxicity risk with statins (simvastatin, atorvastatin) → risk of rhabdomyolysis.
• ⬆️ PDE-5 inhibitors (sildenafil, tadalafil, vardenafil).
• ⬆️ Potentiates warfarin effect (risk of bleeding).
• ⬆️ Levels of protease inhibitors (HIV therapy).
• ⚠️ Contraindicated with terfenadine (risk of arrhythmias).
• Enzyme inducers (rifampicin, phenytoin) ↓ clarithromycin levels.

⚠️ Cautions

• 💔 QT prolongation or concurrent QT-prolonging drugs (e.g. amiodarone, fluoroquinolones, antipsychotics).
• 🧬 Acute porphyria.
• 🫀 Hepatic impairment – monitor LFTs.
• 💧 Severe renal impairment – dose reduction required.

🚫 Contraindications

• Hypersensitivity to macrolides.
• Concurrent use with terfenadine, astemizole, cisapride, pimozide (risk of arrhythmia).
• History of cholestatic jaundice or hepatic dysfunction associated with clarithromycin use.

💥 Side Effects

• 🤢 GI upset – nausea, vomiting, diarrhoea, dyspepsia (less common than erythromycin).
• 🌡️ Rash, urticaria, rare severe skin reactions: Stevens–Johnson syndrome, toxic epidermal necrolysis.
• 🫀 QT prolongation, arrhythmias.
• 🧠 Altered taste/smell, headache, dizziness.
• 🧪 Hepatotoxicity – cholestatic jaundice, hepatitis, pancreatitis.
• 💪 Myalgia, rarely rhabdomyolysis (esp. with statins).
• 🩸 Rare: renal failure, cytopenias.

📑 References

• BNF: Clarithromycin
• MHRA: Macrolides and QT prolongation warnings