71750 Most anticoagulants are associated with adverse drug reactions, concerns for their duration of action, bleeding risk, and the need to carry out monitoring while adjusting dosages during the treatment period. Therefore, selection of appropriate anticoagulant for preventing Atrial Fibrillation must ensure that the practitioner considers these factors. From a therapeutic perspective, reports show that Warfarin is the first line anticoagulant for patients with Atrial Fibrillation (Nice guideline 2012), especially when the condition is primary or severe because it curbs the development of stroke. Besides, reports show that oral administration has had long-term safety for the past 50 years (AABB, 2014). In addition to that, its effect can be reversed with vitamin k antidote in case of bleeding (AABB, 2014). Moreover, warfarin has reduced rates of major gastrointestinal bleeding and myocardial infarction comparing with the novel oral anticoagulants (NHS Information Centre, 2014). Despite its complete absorption after oral administration, Warfarin is slow acting anticoagulant with a long half-life. Its two active enantiomers (R and S forms) have different therapeutic potency, metabolism, and clearance pathways (Hirsh, 2003). Besides, it has a delayed anticoagulant effect from two to 3 days while its duration of action continues for 2 to 5 days after a single dose administration. However, dosing of Warfarin can be described as complicated. this is due to its interaction with some foods containing vitamin K.