First anticoagulant rodenticide is

First anticoagulant rodenticide is Warfarin.
Anticoagulants, commonly known as blood thinners, are chemical substances that prevent or reduce coagulation of blood, prolonging the clotting time.
One of the first anticoagulants, warfarin, was initially approved as a rodenticide. Warfarin is in a class of medications called anticoagulants ('blood thinners'). It works by decreasing the clotting ability of the blood.