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Miconazole gel and warfarin

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Miconazole gel and warfarin

Pharmacists need to take the interaction between oral miconazole gel and warfarin much more seriously, says Daniel Buck, specialist pharmacist, anticoagulation, Wrightington, Wigan and Leigh NHS Foundation Trust

Interaction alert!

Mr X is a 42-year-old male. He has been on warfarin for a long time due to a history of multiple venous thromboembolic events. His target International Normalised Ratio (INR) range is 2.0-3.0. He also has a complex history of cerebral haemorrhage, which has required neuro- surgical interventions. When he visited my warfarin clinic for his routine INR test, it was 16, a dangerously high level,  especially in a patient with a history of cerebral bleeding. The care worker accompanying him showed me the medicines administration chart, which indicated the initiation of miconazole oral gel 14 days previously for simple oral thrush.

Mr X was immediately transferred to hospital and his raised INR reversed with a low dose of vitamin K. He was monitored closely for several days to ensure there was no bleeding, especially given his neurological history. Once his INR was reversed, his anti- coagulation was cautiously re-introduced and his INR stabilised.

Well-documented

This case illustrates the critical nature of interactions of medicines with warfarin even when given topically, unless the right monitoring is put in place to prevent adverse events. When used orally, miconazole gel is systemically absorbed leading to a significant interaction with warfarin via the P450 CYP2C9 pathway. Despite this being a well- documented interaction, it is often overlooked and can lead to patient distress and a loss of belief in the ability of the practitioner supplying the gel.

When prescribers and pharmacists are contacted they often report that they believed the interaction to be insignificant due to the topical nature of the gel. This is often compounded by the fact that the PIL does not inform the patient that warfarin is a contraindication; it merely advises them to inform their doctor, and they often assume the prescriber was aware they were on warfarin and has acted accordingly.

Points for practice

  • The concurrent use of warfarin should be regarded as a contraindication to the use of miconazole oral gel. Community pharmacists should exercise caution when selling it over the counter and should refer all relevant prescriptions back to the prescriber for an alternative
  • Pharmacists should ensure all counter staff are made aware of this serious complication with miconazole’s use and ensure relevant queries are referred to the pharmacist for advice
  • If patients on warfarin report using miconazole oral gel, they should be advised to contact their anticoagulant clinic for an urgent INR.
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