Summary

Maintenance of a patient’s international normalised ratio (INR) within the appropriate target range remains a challenge in clinical practice. The effects of concurrent medication, alcohol and compliance on stable control are well documented. Recent evidence also shows that supplemental vitamin K in patients with low body stores improves the stability of INR in these patients. Here, the case of a 57-year-old with coeliac disease requiring warfarin for a metallic mitral valve, who had poor INR stability resulting in thrombotic and bleeding complications, is described. Her vitamin K body stores were extremely low. Supplementation of vitamin K (100 μg daily) resulted in improvement in anticoagulation stability (mean (SD) 3.41 (1.68) vs 4.68 (3.34)). The percentage time spent within target INR range doubled following vitamin K supplementation. This case illustrates a relatively new approach to managing patients with highly unstable INR levels and provides extra understanding of factors influencing INR stability.