Clarithromycin

What clarithromycin is and how it works

Clarithromycin is a macrolide antibiotic used to treat a range of bacterial infections, including certain respiratory tract infections, skin infections, and (combined with other medicines) Helicobacter pylori stomach infections. It works by stopping susceptible bacteria from making proteins they need to grow. (1) (3)

Clarithromycin is prescribed for a specific bacterial infection and a defined course length -- completing the full course as directed matters for effectiveness and to reduce antibiotic resistance. It carries two genuine cardiovascular warnings worth knowing about: a link to increased mortality appearing a year or more after treatment in people with existing coronary artery disease, and a risk of QT interval prolongation (a heart rhythm effect) that is a recognised effect of this class of antibiotics.

Mechanism of action: how clarithromycin works

Clarithromycin is a semi-synthetic macrolide antibiotic that inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit, giving it bacteriostatic (and at higher concentrations, bactericidal) activity against a range of Gram-positive and some Gram-negative organisms, plus atypical pathogens and H. pylori. (1) (5)

What is Clarithromycin used for?

Before taking clarithromycin

Do not take / not appropriate for

• Do not take clarithromycin if you have had a serious allergic reaction to it or to other macrolide antibiotics. (all countries where authorised) (1)
• Do not take clarithromycin together with cisapride, pimozide, ergot alkaloids, lomitapide, lovastatin, or simvastatin, since dangerous interactions can occur. (all countries where authorised) (1)
• Do not take clarithromycin if you have low blood potassium (hypokalaemia), a history of QT interval prolongation, or a history of dangerous heart rhythm problems (ventricular arrhythmia), unless your clinician has specifically decided the benefit outweighs this risk. (Australia, Canada) (6) (5)
• Do not take clarithromycin if you have had liver problems (jaundice) linked to a previous course of clarithromycin. (all countries where authorised) (1)

Tell your clinician about

• Any heart problems, especially coronary artery disease (heart artery disease), heart rhythm problems, or a family history of QT prolongation.
• Any personal history of low potassium or low magnesium levels.
• Any liver or kidney problems.
• Any history of myasthenia gravis, since clarithromycin can worsen symptoms.
• All other medicines you take, since clarithromycin has many significant drug interactions.
• Whether you are pregnant, planning pregnancy, or breastfeeding.

Clarithromycin dosage and how to take it

• Take exactly as prescribed, at evenly spaced intervals, with or without food depending on the formulation your prescriber recommends.
• Complete the full prescribed course, even if you feel better before it is finished, unless your clinician tells you otherwise -- stopping early can allow the infection to return and contributes to antibiotic resistance.
• Extended-release tablets should be swallowed whole, not crushed or chewed.

Procedures and treatment changes

Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (2) (3) (4) (5) (6) (7)

Missed dose

Take the missed dose as soon as you remember, unless it is nearly time for your next dose, in which case skip the missed dose and continue your normal schedule -- do not take a double dose. Contact your prescriber or pharmacist if you are unsure or have missed several doses.

Overdose

Seek urgent medical attention if you think you have taken too much clarithromycin, especially if you notice an irregular or racing heartbeat, severe nausea/vomiting, or abdominal pain. (1)

Clarithromycin side effects

Side effects and their urgency vary; report severe, persistent, or concerning symptoms.

Serious warnings

Interactions

• Certain statins (lovastatin, simvastatin) and lomitapide must not be combined with clarithromycin due to increased risk of muscle damage/toxicity. (1)
• Cisapride, pimozide, ergot alkaloids, and lurasidone must not be combined with clarithromycin due to serious interaction risks, including cardiac arrhythmia. (1)
• Colchicine combined with clarithromycin can cause serious, potentially fatal toxicity, particularly in patients with kidney or liver impairment. (1)
• Other QT-prolonging medicines (including some antiarrhythmics, antipsychotics, and hydroxychloroquine/chloroquine) can increase the risk of dangerous heart rhythm problems when combined with clarithromycin. (7)
• Warfarin and other blood thinners: clarithromycin can increase their effect, raising bleeding risk, and may need closer monitoring. (3)

Pregnancy, breastfeeding, kidney/liver function, age

Monitoring

Before starting

• Personal/family history of QT prolongation or heart rhythm problems
• Coronary artery disease/heart disease history
• Baseline potassium/magnesium if at risk
• Liver and kidney function if relevant
• Full medication review for interacting drugs

During treatment

• Watch for signs of an abnormal heart rhythm (palpitations, fainting, dizziness).
• Watch for signs of liver problems.
• Watch for severe or persistent diarrhoea, including after finishing the course.
• Complete the full course as directed.

Storage

Store at room temperature, away from moisture and heat, in the original packaging, and out of the reach of children. Oral suspension should be used within the period stated on the label after reconstitution.

Frequently asked questions

References

1. CLARITHROMYCIN tablet -- full prescribing information (Revised 5/2023)U.S. Food and Drug Administration / DailyMed (NIH), full prescribing information · United States · accessed 2026-07-30 · source 1
2. FDA Drug Safety Communication: Clarithromycin and increased risk of heart problems or death in patients with heart disease (February 2018)U.S. Food and Drug Administration -- Drug Safety Communication · United States · accessed 2026-07-30 · source 2
3. Clarithromycin 500mg Film-coated Tablets -- Summary of Product Characteristicselectronic medicines compendium (emc), United Kingdom · United Kingdom · accessed 2026-07-30 · source 3
4. Clarithromycin -- list of nationally authorised medicinal products (PSUSA/00000788)European Medicines Agency (EMA) / CMDh -- periodic safety update single assessment (PSUSA) for clarithromycin · European Union · accessed 2026-07-30 · source 4
5. CLARITHROMYCIN (clarithromycin tablets) -- Health Canada Product MonographsHealth Canada product monographs (multiple manufacturers: Taro, Viatris/Biaxin, generics) · Canada · accessed 2026-07-30 · source 5
6. Clarithromycin (Sandoz, Clarithro, and other brands) -- Product Information and ARTG entries (e.g. 101265, 101271)Therapeutic Goods Administration (TGA), Australia · Australia · accessed 2026-07-30 · source 6
7. KLACID / KLACID IV (clarithromycin) -- New Zealand Data Sheets; MARC review 'Macrolides and cardiovascular death'Medsafe (New Zealand regulator) -- data sheets and Medicines Adverse Reactions Committee (MARC) · New Zealand · accessed 2026-07-30 · source 7

Brand names by country

Single-ingredient clarithromycin names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.

Priority countries