Pentobarb 300 is the trade name for a veterinary preparation of pentobarbital -also known as pentobarbitone - specifically designed to euthanize small animals such as dogs and cats by intracardic injection. Unlike another common preparation of this barbiturate called Nembutal, it has never commercially been used in humans, -at the time of writing- and is only available to veterinarians for humane animal euthanasia.
A characteristic additive is included in Pentobarb 300 and many other euthanasia solutions, to make it more difficult to confuse it with other more therapeutic injectable anaesthetics. The additive is a blue food dye giving Pentobarb 300 its euphemism - blue juice.
A stronger solution is called Pentobarb 500, available to euthanize larger animals such as horses. This concentrated euthanasia solution, capable of knocking down human size animals and above, contains a cheerful red dye for easy identification. It is not intended to be used in animals destined for consumption, as their meat and organs would contain the euthanasia agent in such amounts that it could be fatal to any organism higher in any synthetic food chain.
Some unscrupulous companies which had contracts to dispose euthanized pets from animal shelters, attempted to profit by re-channeling the corpses back upstream in the industrial food system. Some metropolitan areas produced oil drum quantities of pets and these returned through the flesh market to become processed as pet food. Pentobarb was in sufficient concentrations to killed at least some of animals eating the food1.
While Pentobarb remains a popular and effective way to induce euthanasia, so highly regarded that right to death activists have attempted its illegal manufacture from stock materials such as malic acid for their own purposes2 - Pentobarb is a less than perfect method for terminating life. It can cause convulsions and fail to stop cardiac activity for several minutes after administration. Newer euthanasia combinations contain an additional agent - Phenytoin Sodium - used in humans as an anti convulsive agents, and at higher concentrations its cardiotoxic properties are advantageous - quenching heart activity and acting synergistically with Pentobarbital, potentiating the former's effects at lower doses. Further research will no doubt find other ad-mixtures to assist in a rapid and painless death.
1Food Pets Die for: Shocking Facts About Pet Food By Ann N. Martin
2Currently unable to be substantiated.