Clarithromycin

What it is

Clarithromycin is a macrolide antibiotic that blocks the bacterial ribosome, stopping protein synthesis and the bacteria's ability to multiply. It is used for bacterial infections and, as part of combination treatment, for ulcers linked to Helicobacter pylori. It is also a strong inhibitor of the liver enzymes that clear many other medicines.

A usual adult range, not a national label — the dose and the timing differ by country and by product.

Used for

• Bacterial infection
• Ulcer

Approved uses differ by country — some of these may be off-label or unapproved where you live.

What to know while taking it

It can be taken with or without food, but grapefruit is avoided because it compounds the same enzyme blockade and pushes drug levels up. That blockade is why simvastatin and atorvastatin are not combined with it, and why the effect of the anticoagulant warfarin can rise; omeprazole levels also shift, though the two are deliberately paired in ulcer treatment. Probiotics are kept a few hours apart, the course is finished in full, and ALT and creatinine are checked when a prescriber asks for them rather than as a routine part of every course: the liver and kidneys both handle the drug, but the UK MHRA-approved product information reserves liver tests for symptoms such as jaundice or dark urine and kidney tests for known impairment.

When to see a doctor

Because clarithromycin can prolong the QT interval, palpitations, fainting or a markedly irregular heartbeat call for prompt medical attention. Muscle pain or weakness, dark urine, yellow skin or eyes, unusual bruising or bleeding, or severe persistent diarrhoea are reasons to see a doctor.

Worth knowing

• Can prolong the QT interval
• Avoid grapefruit
• Finish the full course
• Take probiotics a few hours apart

Markers to watch

• ALT
• Creatinine