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Macrolide Antibiotic — Respiratory / H. pylori / MAC Pregnancy: Avoid — associated with miscarriage and cardiac defects in some studies; azithromycin preferred macrolide in pregnancy

Clarithromycin

Brand names: Klaricid, Klaricid XL

Adult dose

Dose: CAP/LRTI: 500 mg twice daily orally or IV; H. pylori triple therapy: 500 mg twice daily × 7 days; MAC prophylaxis/treatment: 500 mg twice daily
Route: Oral or IV
Frequency: Twice daily
Max: 1 g/day (standard); 2 g/day in MAC
Macrolide with superior tissue penetration vs erythromycin. Active against atypicals (Mycoplasma, Chlamydophila, Legionella), H. pylori (in triple/quadruple therapy), MAC (Mycobacterium avium complex in HIV). XL modified-release formulation: 500 mg once daily. Strong CYP3A4 inhibitor — numerous drug interactions.

Paediatric dose

Dose: 7.5 mg/kg mg/kg
Route: Oral (granules/suspension)
Frequency: Twice daily
Max: 500 mg per dose
BNFc: licensed from 6 months; suspension 125 mg/5 mL and 250 mg/5 mL available

Dose adjustments

Renal

CrCl <30 mL/min: reduce dose by 50% or double dosing interval

Hepatic

Avoid in severe hepatic impairment — hepatically metabolised; QT prolongation risk

Paediatric weight-based calculator

BNFc: licensed from 6 months; suspension 125 mg/5 mL and 250 mg/5 mL available

Clinical pearls

  • One of the most potent CYP3A4 inhibitors in clinical use — check all co-medications before prescribing; metallic taste is distinctive and helps confirm compliance
  • H. pylori eradication: clarithromycin resistance now >20% in UK — test-and-treat with culture/PCR sensitivity where possible; bismuth quadruple therapy if clarithromycin resistance suspected
  • MACRO trial: azithromycin once-daily prophylaxis superior to clarithromycin for MAC prophylaxis in HIV — but clarithromycin remains active for MAC treatment
  • QT prolongation risk — avoid in hypokalaemia, hypomagnesaemia, and concurrent QT-prolonging agents

Contraindications

  • Concurrent statins metabolised by CYP3A4 (simvastatin, lovastatin — rhabdomyolysis)
  • Concurrent ergotamine/dihydroergotamine (ergotism)
  • QT prolongation / concurrent QT-prolonging drugs
  • History of clarithromycin-associated jaundice

Side effects

  • GI disturbance (nausea, diarrhoea, metallic taste)
  • QTc prolongation
  • Hepatotoxicity (cholestatic jaundice)
  • Dysgeusia (altered taste)
  • C. difficile
  • Rash
  • Hearing loss (high dose)

Interactions

  • Simvastatin/lovastatin — contraindicated (rhabdomyolysis via CYP3A4 inhibition)
  • Warfarin — significantly enhanced INR
  • Digoxin — increased digoxin toxicity
  • Carbamazepine — increased carbamazepine levels
  • Colchicine — life-threatening colchicine toxicity (CYP3A4 inhibition)
  • Statins (atorvastatin) — increase statin levels — reduce dose
  • Tacrolimus/ciclosporin — increased immunosuppressant levels

Monitoring

  • ECG (QTc — especially with concurrent QT-prolonging drugs)
  • LFTs
  • Drug interactions review (CYP3A4)
  • INR if on warfarin

Reference: BNFc; BNF 90; NICE NG238 (H. pylori); BHIVA HIV Guidelines; PHE Antibiotic Guidelines; MHRA CYP3A4 Interactions Alert. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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