Excerpted from the 2000 Report of the AVMA Panel on Euthanasia –

Barbiturates

"Intravenous injection of a barbituric acid derivative is the preferred method for euthanasia in …[many species]. Intraperitoneal injection may be used… Intracardiac injection must only be used if the animal is heavily sedated, unconscious, or anesthetized."

Pentobarbital combinations

"Several euthanasia products are formulated to include a barbituric acid derivative (usually sodium pentobarbital), with added local anesthetic agents or agents that metabolize to pentobarbital. Although some of these additives are slowly cardiotoxic, this pharmacologic effect is inconsequential. These combination products are listed by the DEA as Schedule III drugs, making them somewhat simpler to obtain, store, and administer than Schedule II drugs such as sodium pentobarbital. The pharmacologic properties and recommended use of combination products that combine sodium pentobarbital with lidocaine or phenytoin are interchangeable with those of pure barbituric acid derivatives. A combination of pentobarbital with a neuromuscular blocking agent is not an acceptable euthanasia agent."