Published: June 2011

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Statin interactions: reports of serious myopathy

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Prescriber Update 32(2): 13-14
June 2011

Prescribers are reminded of the potential for serious adverse reactions when statins are prescribed with medicines that inhibit the CYP3A4 isoenzyme.

Recent reports to the Centre for Adverse Reactions Monitoring (CARM) indicate that the concomitant treatment with medicines that interact with simvastatin or atorvastatin has led to serious myopathies. These reports have included life-threatening and fatal cases of rhabdomyolysis. In some cases more than one interacting medicine was prescribed.

The adverse reaction reports describe common situations such as:

• The use of macrolides for acute infection without stopping the patient's regular simvastatin.
• Initiating diltiazem in patients taking over 40 mg simvastatin daily.
• A lack of clarity in the treatment plan when care of the patient is transferred from primary to secondary care.

The metabolism of simvastatin and atorvastatin is affected by inhibitors of CYP3A4, such as macrolide antibiotics, azole antifungals, ciclosporin, amiodarone, protease inhibitors and grapefruit juice. Although diltiazem is considered to be a weak inhibitor of CYP3A4, the risk of adverse reactions increases with higher doses of statin.

A comprehensive list of medicines that interact with simvastatin or atorvastatin can be found in the medicine data sheets at: www.medsafe.govt.nz/Medicines/infoSearch.asp

To further inform prescribers about the management of clinically important statin interactions, the New Zealand Royal College of General Practitioners has published advice on its website: http://www.rnzcgp.org.nz/assets/documents/Publications/JPHC/June-2009/JPHCJune09Insert24WEB.pdf

Acknowledgement: Thank you to Dr Ruth Savage, CARM, New Zealand Pharmacovigilance Centre.