Years ago I worked for a Vet. and for reptiles he used only the second drug of the two drug combo that he used to euthanize dogs and cats. That drug was Sodium Phenobarbital with the first being Acepromazine. However, that was not needed on reptiles. Sodium Phenobarbital was injected into the abdomen of the intended reptile and it worked instantly. Sorry to hear about your sick snake billy...