BACKGROUND: It is not known whether initiation of antidiabetic treatment affects the effect of vitamin K antagonists (VKA). It was previously shown that metformin affects the effect of one VKA, phenprocoumon.
OBJECTIVES: The aim of this study was to determine if initiation of glucose-lowering treatment affects international normalized ratio (INR) and dose requirements of the anticoagulant VKAs warfarin and phenprocoumon.
PATIENTS/METHODS: We performed a self-controlled retrospective register-based study. A total of 118 patients initiating glucose-lowering treatment while being treated with warfarin or phenprocoumon were included in the study. We compared INR, dose/INR and proportion of patients with at least one subtherapeutic INR measurement before and after initiation of glucose-lowering treatment.
RESULTS: Initiation of glucose-lowering drug treatment caused mean INR to decrease from 2.5 to 2.2 (decrease of -0.3 [95% CI: -0.1; -0.5]) and led to more than half of the patients having at least one sub-therapeutic INR measurement. Six to twelve weeks later, the VKA dose/INR was increased by 11%, indicating a weakened effect of the VKA.
CONCLUSION: In conclusion, initiation of glucose-lowering treatment reduces the anticoagulant effect of VKA to an extent that is likely to be clinically relevant. This finding needs confirmation and mechanistic explanation. This article is protected by copyright. All rights reserved.