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Macrolide Antibiotic Pregnancy: Avoid in first trimester — animal studies suggest risk of cardiovascular defects. Use azithromycin in pregnancy if macrolide needed (more safety data).

Clarithromycin

Brand names: Klaricid, Klaricid XL

Adult dose

Dose: Community-acquired pneumonia (CAP): 500mg BD for 5–7 days (oral) or IV in severe cases. H. pylori eradication (as part of triple therapy): 500mg BD for 7 days. Skin/soft tissue infections: 250mg BD for 7 days. Atypical pneumonia (Mycoplasma, Chlamydophila): 500mg BD for 14 days.
Route: Oral / IV
Frequency: Twice daily
Max: 500mg BD (oral); 1g BD (IV — severe infections)
Strong CYP3A4 inhibitor — significant drug interaction burden. Do not use in QT-prolonging drug combinations. XL formulation (500mg OD) available for some indications. Take with food to reduce GI side effects. Not first-line for simple respiratory infections — reserve for penicillin-allergic patients or atypical pathogens.

Paediatric dose

Dose: 7.5 mg/kg
Route: Oral
Frequency: Twice daily
Max: 500mg BD
BNFc: 1 month–11 years: 7.5mg/kg BD (max 500mg BD). 12–17 years: 250–500mg BD. Seek specialist paediatric opinion for severe infections.

Dose adjustments

Renal

eGFR <30: reduce dose by 50% (max 500mg daily); extend dosing interval.

Hepatic

Severe hepatic impairment with renal impairment: avoid. Hepatic impairment alone: use with caution — drug is hepatically metabolised.

Paediatric weight-based calculator

BNFc: 1 month–11 years: 7.5mg/kg BD (max 500mg BD). 12–17 years: 250–500mg BD. Seek specialist paediatric opinion for severe infections.

Clinical pearls

  • Statin interaction: always stop simvastatin and lovastatin during clarithromycin course (contraindicated — rhabdomyolysis risk). Rosuvastatin and pravastatin are safe alternatives as they are not CYP3A4-dependent
  • Colchicine interaction: potentially fatal — clarithromycin + colchicine has caused deaths from bone marrow suppression. Do not co-prescribe; use azithromycin instead if macrolide needed in patient on colchicine
  • H. pylori triple therapy: clarithromycin 500mg + amoxicillin 1g + PPI (lansoprazole 30mg or omeprazole 20mg) all BD for 7 days — first-line eradication
  • Resistance: increasing clarithromycin resistance in H. pylori and Streptococcus pneumoniae — check local resistance patterns

Contraindications

  • QT prolongation or concomitant QT-prolonging drugs
  • Severe hepatic impairment with concurrent renal impairment
  • Hypersensitivity to macrolides
  • Concomitant simvastatin, lovastatin (rhabdomyolysis risk)

Side effects

  • GI upset, nausea, diarrhoea, abdominal pain (common)
  • Metallic taste / taste disturbance
  • QTc prolongation
  • Hepatotoxicity (reversible — raised LFTs)
  • Clostridioides difficile infection (antibiotic-associated diarrhoea)
  • Drug interactions (CYP3A4 inhibition)

Interactions

  • Statins (simvastatin, atorvastatin) — CYP3A4 inhibition causes rhabdomyolysis; stop statins during clarithromycin course (simvastatin/lovastatin contraindicated; atorvastatin max 20mg)
  • Warfarin — increases INR significantly; monitor INR
  • Colchicine — inhibits P-gp and CYP3A4; severe colchicine toxicity (diarrhoea, bone marrow suppression) — avoid or reduce colchicine dose
  • QT-prolonging drugs — additive risk; avoid
  • Digoxin — inhibits P-gp; increases digoxin levels; monitor

Monitoring

  • LFTs if prolonged use
  • QTc (if cardiac risk)
  • Drug interaction review (essential before prescribing)
  • Treatment response (symptom improvement in 48–72h)

Reference: BNFc; BNF 90; NICE CG191 (Pneumonia); NICE CG184 (Dyspepsia/H. pylori); British Thoracic Society CAP Guidelines. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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