Venous Thromboembolism

Inclusion Criteria

- Children aged 6 months  to < 6 years who have been treated for at least 2 months or, in case of catheter related thrombosis, for at least 6 weeks with LMWH (low molecular weight heparin), fondaparinux and/or VKA (vitamin K antagonist) for documented symptomatic or asymptomatic venous thrombosis  - Hemoglobin, platelets, creatinine, alanine aminotransferase (ALT) and bilirubin evaluated within 10 days  prior to randomization
 - Informed consent provided

Exclusion Criteria

-  Active bleeding or high risk for bleeding contraindicating anticoagulant therapy
 - Symptomatic progression of venous thrombosis during preceding anticoagulant treatment
 - Planned invasive procedures, including lumbar puncture and removal of non peripherally placed central lines during study treatment
 - An estimated glomerular filtration rate (eGFR) < 30 mL/min/1.73 m^2  
 - Hepatic disease which is associated with either: coagulopathy leading to a clinically relevant bleeding risk, or ALT> 5x upper level of normal (ULN) or total bilirubin > 2x ULN with direct bilirubin > 20% of the total
 - Platelet count < 50 x 10*9/L
 - Hypertension defined as > 95th age percentile   
 - Life expectancy < 3 months
 - Concomitant use of strong inhibitors of both cytochrome P450 isoenzyme 3A4 (CYP3A4) and P-glycoprotein (P-gp), i.e. all human immunodeficiency virus protease inhibitors and the following azole antimycotics agents: ketoconazole, itraconazole, voriconazole, posaconazole, if used systemically
 - Concomitant use of strong inducers of CYP3A4, i.e. rifampicin, rifabutin, phenobarbital, phenytoin and carbamazepine
 - Hypersensitivity or any other contraindication listed in the local labeling for the comparator treatment or experimental  treatment 
 - Inability to cooperate with the study procedures 
 - Previous randomization to this study 
 - Participation in a study with an investigational drug or medical device within 30 days prior to randomization