⚠️ 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)

Indication	Details
🙂 Mild Infection	Clarithromycin • 250–500 mg PO BD
🔥 Moderate–Severe Infection	Clarithromycin • 500 mg BD IV infusion (into a large proximal vein)
⏳ Course Duration	Typically 7–14 days depending on indication

🔄 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

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Clarithromycin