Clarithromycin
A macrolide for atypical pneumonia, penicillin allergy and H. pylori. Watch for interactions and QT prolongation.
Common brands in Pakistan: Klaricid. Brand availability changes; check with your pharmacy.
On this page
Uses
- Pneumonia (atypical cover, with a beta-lactam in moderate–severe disease).
- Penicillin allergy: chest, throat, skin infections.
- H. pylori eradication.
How it works
Clarithromycin is a macrolide. It binds the 50S subunit of the bacterial ribosome and blocks protein synthesis, which mainly stops bacteria growing rather than killing them outright. It covers streptococci, many staphylococci, Moraxella, some Haemophilus, H. pylori, and the "atypical" organisms (Mycoplasma, Chlamydophila and Legionella) that beta-lactams miss. It is also a strong inhibitor of the liver enzyme CYP3A4, which is the source of most of its dangerous interactions.
When it is used
- Community-acquired pneumonia: as the alternative to amoxicillin in low-severity pneumonia, and added to amoxicillin or co-amoxiclav for atypical cover in moderate or high severity. Use CURB-65 and see community-acquired pneumonia.
- Penicillin allergy: sore throat, chest infection and skin infection.
- H. pylori eradication as part of triple therapy.
- Not for: urinary tract infection, MRSA (not reliable), viral coughs and colds, or typhoid. Do not repeat clarithromycin if a first H. pylori regimen containing it has failed; resistance is common in many countries, including Pakistan.
Adult dose
| Indication | Dose |
|---|---|
| Chest or skin infection | 500 mg orally twice daily for 5–7 days |
| IV | 500 mg every 12 hours |
| H. pylori | 500 mg twice daily with a PPI and amoxicillin or metronidazole for 7–14 days |
Children's dose
7.5 mg/kg twice daily (max 500 mg per dose).
Kidney and liver
Creatinine clearance below 30: halve the dose.
Use with care in liver disease; avoid in severe liver failure combined with kidney impairment.
Pregnancy and breastfeeding
Avoid in pregnancy unless no alternative.
Manufacturers advise against use, particularly in the first trimester, because of animal data; erythromycin or azithromycin are usually preferred when a macrolide is needed. Small amounts pass into breast milk; use only if the benefit outweighs the risk.
Side effects and cautions
- Nausea, taste disturbance, diarrhoea.
- QT prolongation.
- Interactions: statins (stop simvastatin and atorvastatin during treatment or reduce), colchicine (toxicity), warfarin, some calcium channel blockers.
Contraindications
- Known long QT, a history of torsades, or uncorrected low potassium or magnesium.
- Taking simvastatin, ergotamine or ticagrelor; colchicine in a patient with kidney or liver impairment.
More side effects
- Abdominal pain, headache, raised liver enzymes and occasionally cholestatic hepatitis.
- C. difficile diarrhoea, as with any antibiotic.
- Phlebitis with IV use.
More interactions
- Anticoagulants: raises the INR with warfarin; increases levels of rivaroxaban and apixaban.
- Amlodipine, verapamil, diltiazem: low BP and, with the rate-limiting drugs, bradycardia.
- Other QT drugs: quinolones, amiodarone, antipsychotics, ondansetron.
- Carbamazepine, ciclosporin, tacrolimus, digoxin, oral midazolam and sildenafil levels also rise.
Monitoring
- ECG before starting if the patient has heart disease, takes other QT-prolonging drugs or has low potassium. Use the QTc calculator.
- INR within a few days if on warfarin.
- Liver function if the course is long or jaundice develops.
Practical tips
- IV: dilute 500 mg in 250 mL of 0.9% sodium chloride or 5% glucose and give over 60 minutes into a large vein. Never give it as a bolus or IM. Switch to oral once the patient is improving and can swallow.
- Tablets can be taken with or without food; modified-release tablets (once daily) are taken with food.
- Before prescribing, read the drug chart for statins, colchicine, anticoagulants and calcium channel blockers. Withholding simvastatin or atorvastatin for a 5 to 7 day course is simple and safe.
- Children's suspension tastes bitter; mixing with a little juice afterwards helps adherence.
- For FCPS revision, see antibacterial drugs.
Frequently asked questions
What is the clarithromycin dose for pneumonia?
500 mg twice daily, usually for 5 days, often combined with a beta-lactam in moderate to severe pneumonia.
Which drugs interact with clarithromycin?
Statins, colchicine, warfarin, some antiarrhythmics and calcium channel blockers, among others.
Can clarithromycin be taken with atorvastatin?
It is safest to stop atorvastatin (and simvastatin) during the course and restart after it ends. A short pause in statin treatment causes no harm.
Is clarithromycin safe in pregnancy?
It is avoided, especially in the first trimester. Erythromycin or azithromycin are usually chosen when a macrolide is needed in pregnancy.
Clarithromycin or azithromycin for chest infection?
Both cover atypical organisms. Azithromycin is once daily and has fewer interactions; clarithromycin is the macrolide used in most UK pneumonia guidance and in H. pylori regimens.
Used in these guides
Sources
Doses on this page are typical doses from the sources above. Always confirm with a current drug reference, the product leaflet and your hospital protocol, especially in children, pregnancy and kidney or liver disease.
For FCPS Part 1
Revising for FCPS Part 1? Clarithromycin is covered in our textbook chapter Anticoagulants and antiplatelets, with practice MCQs.