Determinants of effective, safe and convenient vitamin K antagonist use

Vitamin K antagonists (VKA) are frequently used anticoagulants. They are very effective in preventing atrial fibrillation related strokes and recurrent venous thrombosis. However, it can be difficult to achieve an optimal balance between the efficacy and side effects (bleeding), as the dose response may vary between and within patients over time. Therefore, their use requires frequent blood monitoring. We aimed to identify subgroups of VKA users with a risk benefit ratio deviating from the total group of patients. This topic has received renewed interest, since the introduction of the non-VKA anticoagulants (NOACs). In general, these are as effective as VKA, and they can be used without routine blood measurements. Likely, the optimal choice of treatment partly depends on the expected quality of VKA control. This thesis showed that individual quality of VKA control could be predicted from baseline characteristics and VKA control during the first four weeks of treatment. In addition, we demonstrated that extreme overanticoagulation is a prelude for inferior quality of VKA control and poor clinical outcome in the next 90 days. We showed that, in contrast to common beliefs, the bleeding risk of VKA hardly increases after the age of 80 years. In a systematic review of the literature it became clear that patients with a VKA related bleed have a better clinical outcome when treated with than without a dosing protocol for prothrombin complex concentrate. Lastly, we found that, despite the frequent blood measurements, VKA use does not have a negative impact on quality of life