Thrombosis in antiphospholipid syndrome is still frequently treated with vitamin K antagonists, with a target international normalized ratio of 2-3. Time in therapeutic range of international normalized ratio of ≥ 70% is considered optimal. Time in therapeutic range among antiphospholipid syndrome patients is not well documented and the clinical consequences of poor international normalized ratio control are uncertain. This study aimed to determine the proportion of vitamin K antagonist-treated antiphospholipid syndrome patients achieving time in therapeutic range ≥ 70%, to define the features associated with poor control and to determine its association with thrombotic and bleeding events.

This medical records review included antiphospholipid syndrome patients treated with vitamin K antagonists, between 2012-2023. The proportion of patients achieving a time in therapeutic range ≥ 70% was determined, and thrombotic and bleeding events were compared between patients with time in therapeutic range ​​≥ 70% vs < 70%.

Sixty seven antiphospholipid syndrome patients were studied. It was observed that 29.9% achieved time in therapeutic range ≥ 70% and 9.1% of patients with 3 or more comorbidities achieved time in therapeutic range values ≥ 70% compared with 40% of patients with less than 3 comorbidities. Fewer recurrent arterial and overall thrombotic events occurred with time in therapeutic range ​​≥ 70%.

A minority of antiphospholipid syndrome patients treated with vitamin K antagonists achieve optimal anticoagulation and are at risk for recurrent thrombotic events, particularly arterial. Presence of multiple comorbidities is associated with poor international normalized ratio control. Careful monitoring of this patient population is warranted.