How Does Rat Poison Work?

Typical active ingredients for rat poisons are are: brodificoum, diphacinone, warfarin, bromadiolone, and others. Most of these products include green dyes for a characteristic appearance; however, dogs and cats have poor color vision and to them these pellets may look like kibbled pet food.
Anticoagulant rodenticides do not produce signs of poisoning for several days after the toxic dose has been consumed. Anticoagulant rodenticides cause internal bleeding. A poisoning victim will show weakness and pallor but bleeding will likely not be obvious externally.
To understand what these poisons do, it is necessary to have some understanding of how blood clots. A blood vessel is sort of like a pipe carrying rapidly flowing blood along its path. The pipe is lined by smooth flat cells called endothelial cells which facilitate the smooth flow of the blood. If the pipe breaks, the structure of the pipe below the lining is exposed to the flowing blood inside. From there the sequence of events is as follows:
The blood vessel automatically constricts and spasms. This restricts the blood flowing to the damaged area and helps minimize blood loss.
The exposed pipe attracts circulating platelets, cloud-like cells that circulate ready to assist in clotting should the need arise. Platelets clump together over the tear in the blood vessel forming a plug within the first 5 minutes of the injury. This is all a good thing but the platelets will stay in place unless a substance called fibrin can be made to bind them.
Platelets have on their surface binding sites for coagulation proteins, which also circulate normally in inactive forms. These coagulation proteins must be activated in order to produce fibrin. There are two ways to do this: a so-called intrinsic pathway and a so-called extrinsic pathway. There are twelve clotting factors involved between these two pathways and we will not confuse you by reviewing these steps but suffice it to say that calcium is one of the factors as are 4 enzymes called serine proteases. It is the serine proteases which are relevant to rat poisoning. The end product of these pathways is protein fiber called fibrin which binds the platelets and serves as a scaffolding for the permanent healing of the vessel tear.
Anticoagulant (containing a chemical called warfarin) impairs the creation of one of the significant blood clotting factors, prothrombin. Vitamin K is an important factor in the synthesis of prothrombin clotting factors in the blood. Because of this, Vitamin K is considered an antidote for warfarin overdose. If a child or pet inadvertently consumes a warfarin-based rodenticide, the usual treatment is injections of Vitamin K. This is simplified greatly because the actual effects of the warfarin can be measured fairly accurately by measuring the blood clotting rate. This prothrombin clotting time or protime measurement is necessary for anyone on warfarin prophylaxis therapy. Tests may be done as frequently as daily to as infrequently as monthly.