Excessive anticoagulation with warfarin or phenprocoumon may have multiple causes

Dan Med J. 2012 Feb;59(2):A4383.


Introduction: Excessive anticoagulation with vitamin K antagonists is a serious condition with a substantial risk of an adverse outcome. We thus found it of interest to review a large case series to characterize the underlying causes of excessive anticoagulation.

Material and methods: Patients were identified both retrospectively and prospectively. The inclusion criteria were an international normalized ratio (INR) > 6.5 or INR > 3.5 and significant bleeding. Patient charts were reviewed for a predefined set of possible causes: Drug-drug interactions, alcohol abuse, disease, start-up or recent change in dosage and dosage errors.

Results: In 86 of 107 admissions one or more causal event were identified. The two most common causes of excessive anticoagulation were disease and drug-drug interactions. The two most common drug-drug interactions were with paracetamol and tramadol. In 44 admissions, a single cause was identified; in 42, two or more causes were identified.

Conclusion: Although it is difficult to identify single initiatives that may reduce the number of admissions due to excessive anticoagulation, interesting areas include a stronger focus on frequent INR control during the various states of disease and heightened attention to drug-drug interactions.

Funding: Not relevant.

Trial registration: Not relevant.

MeSH terms

  • Aged
  • Aged, 80 and over
  • Anticoagulants / adverse effects*
  • Drug Interactions
  • Female
  • Hemorrhage / chemically induced*
  • Hemorrhage / etiology
  • Humans
  • International Normalized Ratio
  • Male
  • Phenprocoumon / adverse effects*
  • Vitamin K / antagonists & inhibitors*
  • Warfarin / adverse effects*


  • Anticoagulants
  • Vitamin K
  • Warfarin
  • Phenprocoumon