Which of the following is NOT used as a drug for euthanasia?

The use of phenobarbital as a euthanasia drug is less common compared to sodium pentobarbital and its derivatives. Sodium pentobarbital is a barbiturate that is widely recognized in veterinary medicine for its ability to induce anesthesia and subsequently euthanasia in a humane manner. It works by depressing the central nervous system, leading to a rapid and painless death.

Sodium pentobarbital derivatives are variations of this drug that maintain similar properties and are also utilized in veterinary practices for euthanasia procedures, ensuring the process is safe and effective.

In contrast, while phenobarbital is a barbiturate and can have sedative effects, it is primarily used for control of epilepsy and not specifically for euthanasia. Due to its different pharmacological profile and indications for use, it does not fit the criteria for a typical euthanasia agent. This distinction helps clarify why it is the correct answer in this context.