Clarithromycin
Brand names: Klaricid, Klaricid XL
Clarithromycin is a macrolide antibiotic indicated for common respiratory, ENT and skin infections and as part of combination therapy for Helicobacter pylori eradication.
Adult dose
Dose adjustments
Creatinine clearance less than 30 mL/min: reduce dose by one-half, i.e. 250 mg once daily, or 250 mg twice daily in more severe infections. Do not continue beyond 14 days in these patients.
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.
Contraindications
- Known hypersensitivity to clarithromycin, other macrolide antibiotics or excipients
- Concomitant ergot alkaloids (ergotamine, dihydroergotamine)
- Concomitant oral midazolam
- Concomitant lomitapide
- Concomitant astemizole, cisapride, domperidone, pimozide or terfenadine (QT prolongation / arrhythmia risk)
- History of QT prolongation (congenital or acquired) or ventricular arrhythmia including torsades de pointes
- Concomitant ticagrelor, ivabradine or ranolazine
- Concomitant CYP3A4-metabolised statins (lovastatin, simvastatin)
- Concomitant colchicine
- Electrolyte disturbances (hypokalaemia or hypomagnesaemia)
- Severe hepatic failure in combination with renal impairment
Side effects
- Abdominal pain
- Diarrhoea
- Nausea
- Vomiting
- Taste perversion (dysgeusia)
Interactions
- Strong CYP3A inhibitor - raises concentrations of CYP3A substrates (e.g. carbamazepine)
- Ergot alkaloids - risk of ergot toxicity (contraindicated)
- Colchicine - risk of colchicine toxicity, deaths reported, especially in elderly/renal impairment (contraindicated)
- CYP3A4-metabolised statins (lovastatin, simvastatin) - myopathy/rhabdomyolysis (contraindicated)
- QT-prolonging drugs and Class IA/III antiarrhythmics (disopyramide, quinidine, dofetilide, amiodarone, sotalol) - risk of QT prolongation / torsades
- Oral midazolam, triazolam - increased sedation (oral midazolam contraindicated)
Clinical monograph
How it works
It inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit and blocking translocation, and is typically bacteriostatic against susceptible organisms.
Prescribing in practice
- Clarithromycin can prolong the QT interval and provoke arrhythmias, so concurrent QT-prolonging medicines and high-risk cardiac patients should be avoided.
- As a strong CYP3A4 inhibitor it is contraindicated with simvastatin and several other agents owing to the risk of serious toxicity.
- It potentiates warfarin and can increase exposure to colchicine and some other co-prescribed drugs.
Monitoring
Monitor clinically for cardiac, hepatic and interaction-related effects rather than by routine bloods in uncomplicated use.
Counselling the patient
- Seek advice if you develop palpitations, blackouts or muscle pain while taking it.
- Always disclose your other medicines, as many interact with clarithromycin.
Evidence & guidelines
The cardiac and interaction cautions for clarithromycin are reflected in MHRA advice and its SPC.
Reference: NICE CKS; 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.
- Centor / McIsaac Score for Strep Pharyngitis · Throat
- FeverPAIN Score for Strep Throat · Throat
- Jarisch-Herxheimer Reaction Severity Assessment · Treatment Reactions
- PID Severity (CDC Diagnostic Criteria) · Gynaecological Infections
- Gustilo-Anderson Classification (Open Fractures) · Fracture Classification
- DRIP Score for Drug-Resistant Pneumonia · Pneumonia
- Infective Endocarditis · ESC 2023 Infective Endocarditis Guidelines; NICE NG41
- Eczema Herpeticum · BAD; NICE CKS
- Suspected Bacterial Meningitis (Adult) · NICE NG240 (2024); NICE NG143 (paeds)
- Clostridioides difficile Colitis · NICE NG199 (2021); IDSA/SHEA 2021
- Returning Traveller — Fever · NaTHNaC; PHE; ESCMID 2018
- Malaria — Diagnosis & Management · PHE 2016; WHO 2023