The purpose of this study is to investigate the preventability of serious adverse drug reactions (ADRs) related to the use of direct oral anticoagulants (DOACs). The investigators also aim at identifying the underlying causes of these preventable ADRs. The endpoint measurements will be compared with a group of patients taking vitamin-K antagonists (VKAs). For this purpose, a protocol for a prospective observational study was developed. The study was approved by the Ethics Committee of the CHU UCL Namur (site Godinne) and the Cliniques Universitaires Saint-Luc. Patients admitted to the emergency department of these two teaching hospitals with a thrombotic or a bleeding event while under DOAC or VKA are included. After a comprehensive medication history, the appropriateness of prescribing is evaluated, using an adapted version of the Medication Appropriateness Index. Causality, severity and preventability of adverse events are assessed by two pharmacists and two hematologists using predefined scales. Second, for cases of serious and preventable ADRs, semi-structured interviews are performed with general practitioners to understand the underlying causes of medication errors. Based on the results, risk-minimization strategies that specifically target the problems encountered in clinical practice will be proposed.

Inclusion Criteria:

• Admitted to the emergency department
• Presenting a thrombotic or a bleeding event
• Prescribed NOAC (rivaroxaban, dabigatran etexilate or apixaban) or VKA