Children Under 2 Years

This is an observational study in which only data are collected from participants receiving their usual treatment. The study is done in children under 2 years old with venous thromboembolism (VTE). VTE is a condition in which blood clots form in the veins, usually in the leg. This can cause pain and swelling. The clot can also break apart and travel in the blood to the lungs where it can block the blood flow. This can be life threatening. Rivaroxaban is approved for doctors to prescribe to children with VTE, but there is limited information about how it is used, how well it works, and how safe it is in children under 2 years old. Children in this study are already receiving or will receive rivaroxaban or other currently used medicines for VTE from their doctor according to the approved product information. The purpose of this study is to collect information on the pattern of use and safety of rivaroxaban and other standard medicines for VTE in children under 2 years old. The main information that researchers will collect in this study: * Age, gender, and other information about the child and their illness * Type of VTE treatment given to the child * Occurrence of medically important bleeding and its severity Further information that researchers will collect: * Changes in the characteristics of the children given VTE treatment (e.g., changes in the age range of children given VTE treatment) and changes in the treatment pattern for VTE * Return of VTE symptoms * Types of doctors who prescribe VTE treatment and their set-up (e.g., special clinics versus hospitals) Besides this data collection, no further tests or examinations are needed in this study. The data for this study will be collected from electronic health records and health insurance claims data until 2026. Researchers will observe each child during treatment until: * end of the anticoagulation treatment period e.g. discontinuation of all study drugs, * their information is no longer available, or * the study ends.

Dravet syndrome is a genetic epilepsy associated with pathogenic variants in SCN1A that codes for Nav1.1, a protein necessary for sodium channels. Children with Dravet syndrome classically present in the first year of life with prolonged seizures, often hemiclonic and in the setting of fever or temperature changes such as getting in or out of bath water. Many anti-seizure medications are sodium channel blockers and exacerbate seizures in this patient population. This creates some limitations in medication choices for this patient population. Recently fenfluramine was approved for use in Dravet syndrome for people 2 years and older. Randomized studies demonstrated a 74.9% reduction of convulsive motor seizures compared to 19.2% in the placebo group. Additionally, 16% of children treated with fenfluramine were seizure free. Fenfluramine is likely to be as effective in children under the age of 2 years. The current study has proposed an intermediate size patient population expanded access protocol to allow access to fenfluramine for children under 24 months of age.