Which of the following drugs should never be used for euthanasia?

Phenobarbital is often used in veterinary medicine for euthanasia due to its ability to induce unconsciousness and suppress neural activity effectively. However, the critical aspect to understand is that while it may be appropriate for this purpose in controlled environments, it is crucial that it is administered properly and by qualified individuals to ensure humane and painless death.

Fentanyl is a potent opioid that can provide analgesia and sedation but is not considered an appropriate choice for euthanasia due to its primary indication for pain management rather than inducing death. It is not used because it does not effectively cause a rapid cessation of life.

Acepromazine is a tranquilizer that may have sedative effects but is not lethal on its own and therefore lacks the efficacy needed for euthanasia. Similarly, ketamine is an anesthetic agent that provides analgesia and sedation but does not reliably bring about death without significant additional agents.

The distinction lies in the fact that while these other drugs may serve therapeutic purposes in pain management or sedation, they do not fulfill the necessary criteria for humane euthanasia as effectively as phenobarbital when used correctly in the right context. The drug selected for euthanasia must ensure a painless and expedient end, which is a primary consideration in veterinary practice.