Issue: 2009 > February > special report

Investigating unexpected INRs: in search of the culprit - Adherence, interactions, genetics, and superwarfarin

P.C.J. Schmeits, , J.H.H. van Geest-Daalderop, M.E. Ouwehand, A.M.J. Coremans, M.H.A. Hermans, J.M.H. Conemans


Treatment with coumarin derivatives is highly
individualised due to high intra- and inter-individual
variation in dose response and risks of severe bleeding
or thromboembolic complications. Treatment focuses on
reaching and maintaining a stable target international
normalised ratio (INR). However, unexpected INRs that are not explained by noncompliance or vitamin K intake may occur. Here we describe seven cases of unexpected INRs, and provide clues that clarify the underlying mechanism.