A new contraindication has been added to the product information of Klacid® (clarithromycin). This product is now contraindicated in patients with hypomagnesaemia.

Clarithromycin is a macrolide antibiotic indicated for the treatment and prevention of various infections caused by susceptible microbes. Like other macrolides, clarithromycin can prolong the QT interval and lead to cardiac arrhythmia and torsades de pointes. This risk is increased in the presence of electrolyte disturbances such as hypomagnesaemia.

Hypomagnesaemia is common in patients who are hospitalised, particularly those who are critically ill. Potential causes of hypomagnesaemia are poor oral intake, gastrointestinal or renal losses, and medications. Medications associated with reduced magnesium levels include diuretics, aminoglycoside antibiotics (e.g. amikacin, gentamicin, tobramycin), cisplatin, amphotericin B, ciclosporin, foscarnet, pentamidine, and proton pump inhibitors (e.g. omeprazole, rabeprazole).

Other risk factors for ventricular arrhythmias that should be considered before administering clarithromycin include:

  • Hypokalaemia;
  • Pre-existing cardiovascular conditions (e.g. coronary artery disease, severe cardiac insufficiency, conduction disturbances, clinically relevant bradycardia);
  • Congenital or documented acquired QT prolongation;
  • History of ventricular arrhythmia; and
  • Other medications associated with QT prolongation.


  1. Electrolyte abnormalities [updated 2021 Mar]. In: Therapeutic Guidelines [digital]. Melbourne: Therapeutic Guidelines Limited; 2021.
  2. Klacid® (clarithromycin) Australian approved product information. Millers Point: Viatris. Approved May 2022.

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