Approximately 30% of patients with an episode of adequately treated deep venous thrombosis (DVT) develop post-thrombotic syndrome (PTS) within 2 years. Studies have shown that the average patient treated with warfarin spends only 60% of the time in his or her goal international normalized ratio (INR) range of 2.0 to 3.0. A recent investigation of the relationship between subtherapeutic INRs and PTS demonstrated that patients who spent more than 50% of their time below an INR of 2.0 had an almost 3-fold risk of developing PTS. Patients in this study were treated with warfarin for at least 3 months and were followed for a maximum of 5 years to assess for signs, symptoms, and severity of PTS.

The authors concluded that low-quality treatment with warfarin is related to the occurrence of PTS in patients with DVT. Strategies aimed at improving the quality of long-term anticoagulation may have the potential to reduce the incidence of this complication.

Dr. Garrett is a clinical pharmacist practitioner at Cornerstone Health Care in High Point, NC.