Advice for healthcare professionals:
bleeding events, some with fatal outcome, have been reported with use of miconazole oral gel by patients on warfarin
patients taking warfarin should not use over-the-counter miconazole oral gel available from pharmacies
if the concomitant use of miconazole oral gel with an oral anticoagulant such as warfarin is planned, exercise caution and ensure that you monitor and titrate the anticoagulant effect carefully
advise patients taking prescription-only miconazole oral gel and warfarin that if they experience signs of over-anticoagulation, such as sudden unexplained bruising, nosebleeds, or blood in urine, they should stop using miconazole and seek immediate medical attention
Review of interaction
The antifungal drug miconazole inhibits several P450 isozymes, including CYP2C9, which can heighten the anticoagulant effect of warfarin and lead to an increase in international normalised ratio (INR) values (and subsequent bleeding complications).
The potential for an interaction between miconazole and warfarin is documented in published literature, with articles describing case reports of interactions dating from the 1980s to 2016. Because of this, warnings are given in the Summaries of Product Characteristics about the potential for drug interactions between anticoagulants/warfarin and azole antifungals (of which miconazole is one) and the need for the anticoagulant effect to be carefully monitored.
In March 2016, the Medicines and Healthcare products Regulatory Agency (MHRA) received a Prevention of Future Deaths (regulation 28) report from a coroner regarding the death of a patient from intracerebral haemorrhage. The coroner raised concerns about the risks for a drug interaction between miconazole oral gel and warfarin, and a possible lack of awareness of the interaction among healthcare professionals.
In response to this report, the MHRA initiated a review of available data about this interaction. The Commission on Human Medicines was asked to advise on whether measures were needed to minimise risk to patients.
While further measures were being considered, an article in Drug Safety Update cautioned that miconazole oral gel is systemically absorbed and can enhance the anticoagulant effects of warfarin, potentially causing bleeding events.
Since the article was published in June 2016, we have received 25 Yellow Card reports, bringing the total possible drug interactions with miconazole and warfarin to 175. The most common events reported have been increased INR (135 reports), contusion (23 reports), and haematuria (19 reports). A fatal outcome was reported in 3 cases.
Our review concluded that to minimise potential risks to patients, the following changes should be implemented:
contraindication of warfarin use for over-the-counter miconazole oral gel, which will also be clearly reflected on the outer carton and on the tube
more prominent and explicit warnings and information about the potential for an interaction between miconazole oral gel and warfarin, and risks associated with concomitant use of these products, throughout the summary of product characteristics and the patient information leaflet, and, for over-the-counter miconazole oral gel, the label (tube and carton)
In the UK, miconazole oral gel is recommended as first-line treatment for localised or mild oral candida (oral thrush) infection in children (aged over 4 months) and adults.
Two miconazole oral gel products are authorised in the UK:
Daktarin Oral Gel is classified as a prescription-only medicine (POM)
Daktarin Oral Gel Sugar Free 2% is classified as a pharmacy (P) medicine available without prescription but only from pharmacies, supplied by or under the supervision of a pharmacist
Warfarin is an oral anticoagulant that has been widely used since the 1950s for prophylaxis of thromboembolic events. Daily dose depends on individual requirements and patients receiving therapy require regular coagulation tests.
Reporting of suspected adverse reactions
Suspected drug interactions between miconazole and anticoagulants such as warfarin should be reported to us on a Yellow Card.
Article citation: Drug Safety Update volume 11 issue 2, September 2017: 1.