Study participants in this study will be recruited because of development of a clot. Clots in pediatric patients are typically treated with blood thinner medicine for 3 months (sometimes longer, depending on confounding factors). It is possible that treatment for 3 months may be longer than needed in children whose clots do not block blood flow through the vein after 6 weeks of treatment.
Over a period of five years, up to 750 children will be enrolled in this study internationally. Each participant will be randomized to a total of 6 weeks or 3 months of venous thrombosis treatment. Doppler ultrasounds of the blood clot will be taken at approximately 6 weeks after diagnosis of the blood clot (the time of the first picture). If the picture at 6 weeks shows that the blood clot is completely blocking blood flow through the vein, the patient will still be followed in the study, but will not be eligible to get the 6 week length of blood thinner treatment. Instead, the patient will receive the usual length of treatment (3 months).
Patients initially positive with an antiphospholipid antibody test that was still positive at approximately 6 weeks after diagnosis of the blood clot, will still be followed in the study, but will not be eligible to get the 6 week length of blood thinner treatment. Instead the primary doctor will decide length of treatment as part of standard care, which will be at least 3 months in total, and possibly much longer.
At the 6 week and 3 month visits, the patient will have an additional 10 mL (2 teaspoons) [for infants: 6 ml, or just over 1 teaspoon] of blood drawn for clotting research tests designed to identify new risk factors for blood clots and their long-term effects.
Blood clots in children are rare when compared to the adult population. However, in the past ten years the increased survival of children with serious illnesses and improved diagnostic techniques have led to an increasing awareness of the occurence and consequences of blood clots in the pediatric population.
Children and adults are thought to share a common physiology of blood clots. In adults several risk factors are known to start one or more of the clotting cascade. The physiology in children is similar but the contribution of each factor differs among age groups. Once a blood clot occurs the progression of hte disease and the aim of antithrombotic (anti-clotting) therapy is the same for both adults and children. These aims are to 1)reduce the risk of death due to blood clots ; 2)reduce the occurence of recurrent blood clots; 3)reduce the occurrence of post clot syndrome by limiting the vascular damage; and 4) maintain vessel patency and vascular access.
Anticoagulation therapy in children can be administered prophylactically to prevent blood clots or in therapeutic doses om those with confirmed blood clots. There is no standard of care for all children for the treatment of blood clots, recommendations include the use of unfractionated heparin, low molecular weight heparin, and/or a vitamin K antagonist.
Apixaban is an orally active factor Xa inhibitor that is being developed for the treatment of venous blood clots in children. The safety and effectiveness profile of Apixaban in other trials indicates a possible benefit to oral apixaban in children over standard of care for the treatment of blood clots. This trial will enroll pediatric patients who require anticoagulation therapy for newly diagnosed blood clots. Subjects will be randomized to receive either apixaban or standard of care. The primary oal of the study is to assess whether apixaban is safe and effective in children for the treatment of blood clots over 12 weeks or over 6 to 12 weeks of therapy in neonates.