Macrolide Antibiotic — Respiratory / H. pylori / MAC Pregnancy: Safety in pregnancy not established; possibility of adverse embryofoetal effects cannot be excluded and some observational studies report increased miscarriage risk. Use during pregnancy not advised without carefully weighing benefits against risks.

Clarithromycin

Brand names: Klaricid, Klaricid XL

Clarithromycin is a macrolide antibiotic used for respiratory tract, skin and soft tissue infections and as a component of Helicobacter pylori eradication regimens.

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

Route: oral

Frequency: twice daily

Max: 500 mg twice daily (severe infections)

Respiratory tract / skin and soft tissue infections: usual dose 250 mg twice daily, may be increased to 500 mg twice daily in severe infections; usual duration 6-14 days. May be given without regard to meals. H. pylori eradication in duodenal ulcer (triple therapy): clarithromycin 500 mg twice daily with e.g. lansoprazole 30 mg twice daily plus amoxicillin 1000 mg twice daily (other PPI/antibiotic combinations described); duration 6-14 days. Children older than 12 years: as for adults. Children younger than 12 years: film-coated tablets not recommended - use clarithromycin paediatric suspension. Elderly: as for adults. Source: 250 mg film-coated tablet SPC.

Dose adjustments

Renal

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 binds the bacterial 50S ribosomal subunit and inhibits protein synthesis, producing a bacteriostatic effect against susceptible Gram-positive cocci and atypical organisms.

Prescribing in practice

Clarithromycin prolongs the QT interval and can cause serious ventricular arrhythmias, so it should be avoided with other QT-prolonging drugs and in patients with relevant cardiac risk factors.
It is a potent inhibitor of cytochrome P450 3A4 and must not be co-administered with simvastatin or certain other contraindicated drugs because of the risk of toxicity such as rhabdomyolysis.
It can enhance the effect of warfarin and raise levels of drugs such as colchicine and certain calcium-channel blockers.

Monitoring

Monitoring is largely clinical, with attention to cardiac, hepatic and interacting-drug effects in at-risk patients.

Counselling the patient

Report palpitations, fainting or unexplained muscle pain and weakness.
Tell your pharmacist about all other medicines because clarithromycin interacts with many drugs.

Evidence & guidelines

MHRA guidance highlights clarithromycin's QT-prolongation and cytochrome P450 interaction risks, which are well documented.

Reference: NICE NG238 (H. pylori); BHIVA HIV Guidelines; PHE Antibiotic Guidelines; MHRA CYP3A4 Interactions Alert; 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).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways