eMJA: Metformin and serious adverse effects

Winston Chong

Chair, Interventional Radiology Reference Group, Level 9, 51 Druitt Street, Sydney, NSW 2000. ranzcrATranzcr.edu.au

To the Editor: I refer to the recent editorial on “Metformin and serious adverse effects”.1

I would like to highlight the position of the Royal Australian and New Zealand College of Radiologists (RANZCR) on the use of metformin hydrochloride when administering intravascular contrast media. The RANZCR has adopted an evidence-based approach in formulating its guidelines. The College guidelines on metformin hydrochloride and intravascular contrast media are available at <www.ranzcr.edu.au/open/policies/diagnostic_imaging/pol1_2.htm>.

The current guideline is that there is no need for patients to stop taking metformin hydrochloride for 24–48 hours before administration of an intravascular contrast medium. Stopping or continuing to take metformin depends on the patient’s renal status, and the likelihood of inducing renal dysfunction when intravascular contrast is administered. If discontinuation is required, then the drug only needs to be stopped for 48 hours, commencing on the day of administration of intravascular contrast.

Janelle C Nisbet,* Joanna M Sturtevant,† Johannes B Prins‡

* Endocrinology Registrar, † Renal Specialist Pharmacist, ‡ Director of Diabetes and Endocrinology; and Professor of Endocrinology, University of Queensland, Princess Alexandra Hospital, Ipswich Road, Woolloongabba, QLD 4102. jprinsATsoms.uq.edu.au

In reply: Chong’s letter highlights some important issues, and his points are well made. As we imply in our editorial,1 the evidence base on which to base guidelines and decisions is poor, which is one of the reasons that the guidelines differ widely between countries and organisations. Specialty-specific guidelines must also take into account practicalities. We elected to follow the more conservative end of the guideline spectrum in our suggestions, accepting that, in many circumstances, these would be difficult or impossible to follow. From a radiological perspective, it would require a significant change in practice to implement guidelines such as those we suggested, and the evidence base supporting such a change does not exist.

Metformin is a short-acting drug and stopping it at the time of a potentially hazardous procedure will almost always be effective in preventing drug-related complications. Overall, the aim of our article was to raise awareness of the potential hazards of metformin use, and to encourage practitioners to follow available and relevant guidelines.