Clarithromycin

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.