Several new oral direct anticoagulants have been recently marketed. However, only a few, limited, studies have provided data about the pharmacology of new oral direct anticoagulants in older persons. This study try to better define wether the pharmacology of each of these 3 drugs (dabigatran, rivaroxaban and apixaban) is actually significantly different in very older patients (over 80) and to which extend. The investigators also try to characterize the main determinants (age, weight, renal function, co-morbidities, etc) of the variability observed between individuals in their response to he drugs studied. The method employed is a population pharmacokinetic/pharmacodynamic study.

Several new oral direct anticoagulants have been recently marketed. A main indication for taking these drugs is atrial fibrillation and, in everyday practice, most patients with atrial fibrillation are older people. However, only a few, limited, studies have provided data about the pharmacology of new oral direct anticoagulants in older persons. Furthermore, this limited data strongly suggests that, in older patients, mean concentrations, overall exposition and half-live of these drugs are increased, as compared with younger people. This study try to better define wether the pharmacology of each of these 3 drugs (dabigatran, rivaroxaban and apixaban) is actually significantly different in very older patients (over 80) and to which extend. The investigators also try to characterize the main determinants (age, weight, renal function, co-morbidities, etc) of the variability observed between individuals in their response to he drugs studied. The method employed is a population pharmacokinetic/pharmacodynamic study. This is, many people (projected 225 patients) will have a few blood samples each and all data will be pooled using statistical methods specific to this kind of studies. Each patient will have one to five blood samples, taken at te same time that routine blood analysis, to determine plasma concentrations of the studied drug. In addition, patients will be followed for thrombotic and haemorrhagic events at 6 and 12 months.

Inclusion Criteria:

• Age 80 years or older
• Under treatment with dabigatran, rivaroxaban or apixaban
• For non-valvular atrial fibrillation

Exclusion Criteria:

• Mechanical (non-biological) heart valve
• Any severe condition leading to a short estimated life expectance (a few months)

Patients aged 80 years or older under treatment with dabigatran, rivaroxaban or apixaban because atrial fibrillation