Published: 6 September 2013

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Reminder: Warfarin and Miconazole Oral Gel

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Prescriber Update 34(3):32
September 2013

Loss of anticoagulant control is one of the most frequent causes of medicine-related hospital admissions in New Zealand. In many cases, an agent which alters the anticoagulant effect of warfarin is implicated¹.

The risk of interactions was highlighted recently in two serious case reports submitted to the Centre for Adverse Reactions Monitoring (CARM). Both patients were taking warfarin and had miconazole oral gel added to their treatment regimes. The addition of miconazole oral gel resulted in an increased INR and haemorrhage. Both patients required hospitalisation.

The interaction between warfarin and miconazole tablets is a well-established and potentially serious interaction. Importantly, this interaction can also occur with miconazole oral gel applied solely to the mouth due to absorption via mucosal surfaces.

CARM has received 16 reports of adverse effects in association with miconazole oral gel and warfarin. Of these reports, three were life-threatening and ten patients required hospitalisation. The majority of cases resulted in an increase in INR and bleeding.

Miconazole inhibits the metabolism of warfarin through the liver by inhibiting the cytochrome P450 isoenzyme, CYP2C92. This can result in an increase and/or prolongation of the effects of warfarin, including adverse effects such as bleeding².

Miconazole oral gel is a commonly supplied pharmacist-only medicine, as well as being available on prescription.

Healthcare professionals are reminded of this potentially serious interaction. Healthcare professionals are advised to avoid miconazole oral gel in patients taking warfarin. If the concomitant use of miconazole oral gel and warfarin is necessary, the patient’s INR should be carefully monitored and the dose of warfarin adjusted as required.

References

1. Best Practice Advocacy Centre. 2007. Interactions with warfarin. Best Practice Journal 4: 28–31. URL: www.bpac.org.nz/magazine/2007/april/pdfs/bpj4_warfarin_pages_28-31_pf.pdf (accessed 6 August 2013).
2. Stockley IH. 2002. Stockley's Drug Interactions. London: Pharmaceutical Press.