How do rodenticides with delayed effect work?
These poisons prevent recirculation of vitamin K and thus formation of prothrombin which is essential for coagulation of blood and are required for maintaining the integrity of capillaries. The depletion of vitamin K is slow and in a couple of days internal hemorrhage occurs extensively and the animal dies of shock. Early recognition of poisoning in humans and other animals can easily be treated with administration of vitamin K. 
http://en.m.wikipedia.org/wiki/Rodenticide