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Macrolide antibiotic

Clarithromycin 500mg (Atypical CAP)

Brand names: Klaricid (250 mg and 500 mg tablets), Klaricid XL (500 mg modified release)

This is clarithromycin used as a macrolide antibacterial for respiratory tract infection, including cover for atypical pathogens in community-acquired pneumonia. It may be used alone for atypical cover or added to a beta-lactam in more severe pneumonia.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

Clinical monograph

How it works

Clarithromycin inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit, giving activity against typical respiratory bacteria and atypicals such as Mycoplasma, Chlamydophila, and Legionella. Its action is largely bacteriostatic.

Prescribing in practice

  • It prolongs the QT interval and is a potent CYP3A4 inhibitor, so review for QT-prolonging and interacting drugs (notably statins, which should be paused, and certain anticoagulants) before prescribing.
  • Avoid in known macrolide hypersensitivity and use with caution in significant cardiac or hepatic disease and electrolyte disturbance.
  • Adjust the dose in significant renal impairment in line with current prescribing references.

Monitoring

Monitor clinical response, liver function on prolonged courses, and ECG or electrolytes where there is additional QT risk.

Counselling the patient

  • Complete the full prescribed course even once you feel better.
  • Report palpitations, fainting, jaundice, or severe diarrhoea.
  • Mention all other medicines, as clarithromycin interacts with many drugs.

Evidence & guidelines

NICE community-acquired pneumonia guidance positions a macrolide such as clarithromycin for atypical cover, alone or combined with a beta-lactam by severity.

Reference: NICE NG120 Pneumonia; NICE CKS LRTI; BTS CAP Guidelines 2009 (updated); Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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