Macrolide Antibiotic Pregnancy: Safety in pregnancy not established; possibility of adverse effects on embryofoetal development cannot be excluded and some studies report increased miscarriage risk. Use during pregnancy not advised without carefully weighing benefits against risks. Excreted into breast milk in small amounts (safety in breast-feeding not established).

Clarithromycin

Brand names: Klaricid, Klaricid XL

Used in: Pneumonia Cellulitis & Skin Infection

Clarithromycin is a macrolide antibiotic for respiratory, skin and other infections, and 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: Respiratory tract and skin/soft tissue infections: 250 mg twice daily, increased to 500 mg twice daily in severe infections

Route: Oral

Frequency: Twice daily

Max: 500 mg twice daily (per SPC; higher combination regimens for H. pylori as above)

General-medicine (film-coated tablet) context. Usual duration 6 to 14 days. Children older than 12 years: as for adults; children under 12 years should use clarithromycin paediatric suspension (film-coated tablets not recommended under 12). May be given without regard to meals. H. pylori eradication in duodenal ulcer (adults), triple therapy: clarithromycin 500 mg twice daily plus a proton pump inhibitor (e.g. lansoprazole 30 mg twice daily or omeprazole) with amoxicillin 1000 mg twice daily or metronidazole 400 mg twice daily; usual duration 6 to 14 days.

Dose adjustments

Renal

CrCl <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.

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

Hypersensitivity to clarithromycin, other macrolides, or any excipient
Concomitant ergot alkaloids (ergotamine, dihydroergotamine)
Concomitant oral midazolam, lomitapide; astemizole, cisapride, domperidone, pimozide, terfenadine (QT prolongation risk); ticagrelor, ivabradine, ranolazine
Concomitant CYP3A4-metabolised statins (lovastatin, simvastatin) and colchicine
History of QT prolongation or ventricular arrhythmia (including torsades de pointes); electrolyte disturbance (hypokalaemia/hypomagnesaemia); severe hepatic failure combined with renal impairment

Side effects

Abdominal pain
Diarrhoea
Nausea
Vomiting
Taste perversion (dysgeusia)

Interactions

Ergot alkaloids, oral midazolam, lomitapide (contraindicated)
Astemizole, cisapride, domperidone, pimozide, terfenadine - QT prolongation (contraindicated)
Simvastatin/lovastatin, colchicine, ticagrelor, ivabradine, ranolazine (contraindicated)
Strong CYP3A inhibitor: increases plasma concentrations of CYP3A substrates

Clinical monograph

How it works

It inhibits bacterial protein synthesis by binding the 50S ribosomal subunit.

Prescribing in practice

It is a potent CYP3A4 inhibitor with major interactions — it raises the levels of some statins (the statin is usually paused during the course to avoid myopathy/rhabdomyolysis) and interacts with warfarin, some calcium-channel blockers and others.
It can prolong the QT interval — caution with other QT-prolonging drugs.
It is an option in some penicillin-allergic patients per local guidance.

Monitoring

Review interactions before prescribing; consider QT risk factors.

Counselling the patient

Tell your clinician all the medicines you take — some (such as certain statins) are paused during the course.
Report palpitations or unexplained muscle pain.

Evidence & guidelines

Used per local antimicrobial and H. pylori guidance (NICE), with careful attention to drug interactions.

Reference: NICE CG191 (Pneumonia); NICE CG184 (Dyspepsia/H. pylori); British Thoracic Society CAP 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).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Drugs

Pathways