Skip to content
ClinCalc Pro
Menu
Calculators Drugs Pathways AI Dx Donate Get the App
Macrolide antibiotic

Clarithromycin (ENT Indications)

Brand names: Klaricid

Used in: Pneumonia Cellulitis & Skin Infection

Clarithromycin is a macrolide antibiotic used for respiratory and ENT infections, as part of Helicobacter pylori eradication, and as a penicillin alternative in some indications.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 250 mg twice daily, increased to 500 mg twice daily in severe infections; usual duration 6 to 14 days
Route: Oral (250 mg film-coated tablets)
Frequency: Twice daily (every 12 hours)
Max: Maximum 500 mg twice daily for respiratory tract or skin and soft tissue infections — the highest dose stated for these indications in either label
SCOPE: this covers the ORAL route for respiratory tract (including upper respiratory tract / ENT) and skin and soft tissue infections only. The bundle contains no intravenous SPC, so the IV dosing shown elsewhere on this page is NOT sourced here and must be verified separately. eMC §4.2 verbatim: 'Patients with respiratory tract/skin and soft tissue infections. Adults: The usual dose is 250 mg twice daily although this may be increased to 500mg twice daily in severe infections. The usual duration of treatment is 6 to 14 days.' Children older than 12 years: 'As for adults.' Administration: 'Clarithromycin may be given without regard to meals as food does not affect the extent of bioavailability.' Elderly: 'As for adults.' US label §2.2 Table 1 gives the individual ENT/respiratory doses, every 12 hours: pharyngitis/tonsillitis 250 mg for 10 days; acute maxillary sinusitis 500 mg for 14 days; community-acquired pneumonia 250 mg for 7-14 days; acute bacterial exacerbation of chronic bronchitis 250 to 500 mg for 7-14 days; uncomplicated skin and skin structure infections 250 mg for 7-14 days. NOT COVERED BY THIS DOSE: H. pylori eradication (eMC: clarithromycin 500 mg twice daily with lansoprazole 30 mg twice daily plus amoxicillin 1000 mg twice daily or metronidazole 400 mg twice daily; or with omeprazole 40 mg daily plus amoxycillin 1000 mg twice daily or metronidazole 400 mg twice daily; or with omeprazole 20 mg daily plus amoxycillin 1000 mg twice daily; usual duration 6 to 14 days) and mycobacterial infection (US label §2.5: 500 mg every 12 hours in adults).

Paediatric dose

Dose: 15 mg/kg/day/kg
Route: Oral
Frequency: Divided every 12 hours (i.e. two divided doses per day), for 10 days
Max: Maximum 1000 mg in 24 hours — US label §2.4 caps the paediatric dosage at 'up to the adult dose', and the adult dose for these indications is 250 to 500 mg every 12 hours (i.e. at most 500 mg twice daily)
THIS IS A DAILY TOTAL (mg/kg/day), not a per-dose figure — divide by two for each 12-hourly dose. US FDA label §2.4 Pediatric Dosage verbatim: 'The recommended daily dosage is 15 mg/kg/day divided every 12 hours for 10 days (up to the adult dose).' US §8.4 states safety and effectiveness are established in patients 6 months and older for pharyngitis/tonsillitis, community-acquired pneumonia, acute maxillary sinusitis, acute otitis media and uncomplicated skin and skin structure infections, and are NOT established under 6 months of age. A DIFFERENT per-dose figure exists for a DIFFERENT indication and must not be used here: US §2.5 gives 7.5 mg/kg every 12 hours up to 500 mg every 12 hours for MYCOBACTERIAL infections only. FORMULATION: the UK SPC in this bundle is for film-coated tablets and states 'Use of Clarithromycin film-coated tablets is not recommended for children younger than 12 years... children under 12 years of age should use clarithromycin paediatric suspension.' No paediatric suspension strength is pinned anywhere in this bundle (the only strengths given are 250 mg and 500 mg tablets), so no concentration is asserted and no volume can be calculated from this source — read the strength off the product in use. Verify all under-18 dosing against a children's formulary before prescribing.

Dose adjustments

Renal

eMC §4.2 verbatim: 'In patients with renal impairment with creatinine clearance less than 30 mL/min, the dosage of clarithromycin should be reduced by one-half, i.e. 250 mg once daily, or 250 mg twice daily in more severe infections. Treatment should not be continued beyond 14 days in these patients.' eMC §4.4 adds that caution should be exercised when administering clarithromycin to patients with moderate to severe renal impairment. US label §2.6 Table 2: severe renal impairment (CLcr <30 mL/min) reduce the dosage by 50%; moderate renal impairment (CLcr 30 to 60 mL/min) taking concomitant atazanavir or ritonavir-containing regimens reduce by 50%; severe renal impairment taking concomitant atazanavir or ritonavir-containing regimens reduce by 75%.

Hepatic

No numeric hepatic dose reduction is given in either label. eMC §4.3 contraindicates use in 'patients who suffer from severe hepatic failure in combination with renal impairment'. eMC §4.4: 'caution should be exercised in administering this antibiotic to patients with impaired hepatic function'; hepatic dysfunction including increased liver enzymes and hepatocellular and/or cholestatic hepatitis, with or without jaundice, has been reported, may be severe and is usually reversible, and cases of fatal hepatic failure have occurred. Patients should be advised to stop treatment and contact their doctor if signs and symptoms of hepatic disease develop, such as anorexia, jaundice, dark urine, pruritus, or tender abdomen.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Paediatric weight-based calculator

THIS IS A DAILY TOTAL (mg/kg/day), not a per-dose figure — divide by two for each 12-hourly dose. US FDA label §2.4 Pediatric Dosage verbatim: 'The recommended daily dosage is 15 mg/kg/day divided every 12 hours for 10 days (up to the adult dose).' US §8.4 states safety and effectiveness are established in patients 6 months and older for pharyngitis/tonsillitis, community-acquired pneumonia, acute maxillary sinusitis, acute otitis media and uncomplicated skin and skin structure infections, and are NOT established under 6 months of age. A DIFFERENT per-dose figure exists for a DIFFERENT indication and must not be used here: US §2.5 gives 7.5 mg/kg every 12 hours up to 500 mg every 12 hours for MYCOBACTERIAL infections only. FORMULATION: the UK SPC in this bundle is for film-coated tablets and states 'Use of Clarithromycin film-coated tablets is not recommended for children younger than 12 years... children under 12 years of age should use clarithromycin paediatric suspension.' No paediatric suspension strength is pinned anywhere in this bundle (the only strengths given are 250 mg and 500 mg tablets), so no concentration is asserted and no volume can be calculated from this source — read the strength off the product in use. Verify all under-18 dosing against a children's formulary before prescribing.

Verify in a children's formulary

US labelling (FDA)

Reference — US labelling, may differ from UK

Adults : clarithromycin tablets 250 mg or 500 mg every 12 hours for 7 to 14 days ( 2.2 ) H. pylori eradication (in combination with lansoprazole/amoxicillin, omeprazole/amoxicillin, or omeprazole): clarithromycin tablets 500 mg every 8 or 12 hours for 10 to 14 days. See full prescribing information (FPI) for additional information. ( 2.3 ) Pediatric Patients : clarithromycin 15 mg/kg/day divided every 12 hours for 10 days ( 2.4 ) Mycobacterial Infections : clarithromycin tablets 500 mg every 12 hours; clarithromycin tablets 7.5 mg/kg up to 500 mg every 12 hours in pediatric patients ( 2.5 ) Reduce dose in moderate renal impairment with concomitant atazanavir or ritonavir-containing regimens …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2025-10-15. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Contraindications

  • Known hypersensitivity to clarithromycin, to other macrolide antibiotic drugs, or to any of the excipients (eMC §4.3)
  • Concomitant ergot alkaloids (e.g. ergotamine or dihydroergotamine) — may result in ergot toxicity (eMC §4.3)
  • Concomitant oral midazolam (eMC §4.3)
  • Concomitant lomitapide (eMC §4.3)
  • Concomitant astemizole, cisapride, domperidone, pimozide or terfenadine — risk of QT prolongation and cardiac arrhythmias including ventricular tachycardia, ventricular fibrillation and torsades de pointes (eMC §4.3)
  • History of QT prolongation (congenital or documented acquired) or ventricular cardiac arrhythmia, including torsades de pointes (eMC §4.3)
  • Concomitant ticagrelor, ivabradine or ranolazine (eMC §4.3)
  • Concomitant statins extensively metabolised by CYP3A4 (lovastatin or simvastatin) — increased risk of myopathy including rhabdomyolysis (eMC §4.3)
  • Concomitant colchicine, as with other strong CYP3A4 inhibitors (eMC §4.3)
  • Electrolyte disturbances (hypokalaemia or hypomagnesaemia), due to the risk of prolongation of the QT interval (eMC §4.3)
  • Severe hepatic failure in combination with renal impairment (eMC §4.3)
  • US label §4 additionally lists history of cholestatic jaundice or hepatic dysfunction with prior clarithromycin use

Side effects

  • Most frequent and common in both adults and children (eMC §4.8): abdominal pain, diarrhoea, nausea, vomiting and taste perversion — usually mild in intensity
  • Common (eMC §4.8): insomnia, dysgeusia, headache, vasodilatation, rash, hyperhidrosis, abnormal liver function tests, injection-site reactions with the injectable form
  • Uncommon (eMC §4.8): candidiasis, vaginal infection, gastroenteritis, cellulitis; leukopenia, neutropenia, eosinophilia, thrombocythaemia; anaphylactoid reaction and hypersensitivity; anorexia and decreased appetite; anxiety and nervousness; dizziness, somnolence, tremor, loss of consciousness, dyskinesia; vertigo, impaired hearing, tinnitus
  • Uncommon/serious cardiac (eMC §4.8): cardiac arrest, atrial fibrillation, electrocardiogram QT prolonged
  • Not known (eMC §4.8): pseudomembranous colitis, erysipelas; agranulocytosis, thrombocytopenia; anaphylactic reaction, angioedema; psychotic disorder, confusional state, depersonalisation, depression, disorientation, hallucination, abnormal dreams, mania; convulsion, ageusia, parosmia, anosmia, paraesthesia; deafness
  • US label §5 highlights: severe acute hypersensitivity reactions (discontinue if they occur) and QT prolongation (avoid in patients with known QT prolongation)

Monitoring

  • Liver: watch for signs and symptoms of hepatic disease (anorexia, jaundice, dark urine, pruritus, tender abdomen) and stop treatment if they develop (eMC §4.4); abnormal liver function tests are a listed common adverse reaction (§4.8)
  • Cardiac/ECG: clarithromycin prolongs the QT interval — avoid in known QT prolongation and correct hypokalaemia/hypomagnesaemia before use (eMC §4.3/§4.4; US §5)
  • Renal function: dose must be halved if creatinine clearance is below 30 mL/min, and treatment not continued beyond 14 days in those patients (eMC §4.2)
  • Drug interactions: clarithromycin inhibits CYP3A, so co-administered CYP3A substrates may reach raised concentrations and need review or dose adjustment (US §7)
  • Diarrhoea: consider Clostridioides difficile-associated diarrhoea / pseudomembranous colitis in any patient who develops diarrhoea on or after treatment (eMC §4.4/§4.8)

Clinical monograph

How it works

Clarithromycin binds the bacterial 50S ribosomal subunit, inhibiting protein synthesis (bacteriostatic at usual concentrations).

Prescribing in practice

  • It is a strong CYP3A4 inhibitor with many important interactions — notably statins (myopathy risk), some DOACs, and other QT-prolonging drugs.
  • It can prolong the QT interval; use caution with other QT-prolonging agents and in electrolyte disturbance.
  • Reduce the dose in significant renal impairment.

Monitoring

Short courses need no routine monitoring; review interacting drugs (e.g. temporarily withholding certain statins) and consider ECG/electrolytes where QT risk is high.

Counselling the patient

  • Complete the course; gastrointestinal upset and a metallic taste are common.
  • Tell your clinician about all other medicines, as clarithromycin interacts with many.

Evidence & guidelines

Macrolides are recommended where a penicillin is unsuitable and within H. pylori eradication regimens, subject to local guidance and interaction checks.

Reference: PHE ENT Antimicrobial Guidelines; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

Calculators
Drugs
Pathways