Compassionate Use of Osocimab in Preventing Thrombotic Complications Without Incremental Bleeding: A Case Report

Being fully CVC-dependent since birth, our patient repeatedly developed catheter-related thrombosis (CRT) since infancy and was treated with daily low-molecular-weight heparin injections for more than 15 years. Despite this, clotting, severe gastrointestinal bleeding, and osteoporosis remained a persistent problem, causing numerous hospitalizations over the years, significant developmental delays, and a decline in the patient's body mass index (BMI). A short period of rivaroxaban treatment had to be stopped owing to acute gastrointestinal bleeding. After the failure of all approved anticoagulant concepts, compassionate use access was granted to the investigational drug osocimab, a human monoclonal antibody inhibitor of factor XIa. Hereditary FXI deficiency as well as FXI inhibition in animal models have been shown to reduce arterial and venous thrombosis without increasing bleeding. Consistent with this, short-term osocimab treatment has shown clinical efficacy in preventing postoperative venous thromboembolism after knee replacement surgery and in reducing dialysis conduit clotting compared with placebo in patients undergoing hemodialysis, without increasing the rate of clinically relevant bleeding versus comparators. After initiating osocimab, the patient experienced no further clotting complications, and bleeding decreased in frequency and severity. The patient's BMI decline immediately stopped; her weight increased by over 10% in the subsequent 20 months, and menstruation started 3 months later without signs of menorrhagia. Now, with 2.5 years of uninterrupted exposure outside of a clinical trial, this patient has experienced the longest duration of factor XIa inhibition to date. She continues to receive osocimab under the compassionate use program and maintains a positive change in her well-being and quality of life.