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The international normalised ratio (INR) is a simple test commonly used by dentists to gauge the likelihood that a patient taking warfarin will have excessive haemorrhage following tooth extraction. There is a clearly defined range of INR values within which simple local post-extraction measures, such as suturing, pressure and tranexamic acid mouth rinses, are adequate to control bleeding. Patients within this range can continue warfarin.1

The large variation in INR values, related to genetic and dietary factors, particularly the intake of vitamin K, reinforces the need to have this test undertaken shortly before the dental procedure.

The metabolism of warfarin can be reduced by azole antifungals such as miconazole. Topical oral miconazole can profoundly increase the INR and thus the risk of bleeding due to over anticoagulation.2,3 Similarly metronidazole, which is commonly used in the management of oral infections, can greatly increase the INR. Dentists therefore need to review patients' current medication before prescribing any drugs, even those topically applied, for possible interactions with warfarin.


  1. Therapeutic Guidelines: Oral and Dental. Version 1. Melbourne:Therapeutic Guidelines Limited; 2007.
  2. Pemberton MN, Oliver RJ, Theaker ED. Miconazole oral gel and drug interactions. Br Dent J 2004;196:529-31.
  3. Morgan L. Topical drug with systemic risk. Aust Prescr 2003;26:35.