Killing me softly: Chemical (drug) euthanasia for pets 101

Patty Khuly, DVM
Updated: March 06, 2017
Published: September 26, 2008
Share this:

This past Monday’s post on euthanasia raised a discussion on the merits and pitfalls of various euthanasia methods. It also brought up some misconceptions as to how the various drug cocktails used to effect euthanasia actually work.

It seems incredible to me that before this week I never thought to post on the mechanics of death in veterinary settings. I hope to rectify this lapse with an abbreviated (but hopefully relatively comprehensive) and clarifying post on this issue.

The two injection method

The currently favored method of euthanasia in veterinary private practice settings is that of the so-called “two injection method.”

In this approach an initial injection is given, either in the vein (IV) or in the muscle (IM), to achieve extreme sedation. A second injection is then administered IV to overdose the animal with an anesthetic drug.

Both injections are considered “overdoses” of medications we normally use in veterinary practice for sedation, tranquilization and/or anesthesia, but not every veterinarian uses the same drugs. Here’s a brief run-down of the commonest drugs we use:

The first injection: Profound sedation

Telazol: Telazol is a pre-mixed cocktail of two drugs (tiletamine and zolazepam), which is a very common sedative for both cats and dogs. Tiletamine is considered a dissociative anesthetic and zolazepam is a valium-like drug in the family of benzodiazepines.

Neither drug is very pain-relieving and yet, together, they lead to an extremely effective sedation that approximates complete anesthesia. When administered as an overdose as part of euthanasia, a complete anesthesia results (no pain can be felt).

Ketamine: Ketamine is a dissociative anesthetic (which technically means that the brain and body are experienced separately by the patient) most often combined with valium to produce the same effect as Telazol. Ketamine, however, has some pain-relieving effects, which makes this combination preferable to some veterinarians for routine use during medical procedures.

As an overdose, however, as in the case of euthanasia, the physiological differences between ketamine/valium and Telazol are considered minuscule. Often, Telazol is preferred in these cases because it is not as rigidly controlled by the Drug Enforcement Agency as ketamine  (a commonly abused “club drug” many vets don’t want to keep around in large quantities for safety reasons).

Propofol: Another drug we use commonly to induce anesthesia, propofol is not commonly abused and it’s ubiquitous to most practices. The problem is that propofol (nicknamed “milk of amnesia” for its white coloration) is relatively expensive. Many vets, however, keep the remains of their one-use-only vials to use as the first injection in the two injection method of euthanasia. This recycling of medications is considered ethical, safe and highly effective, even if we’d never reuse these vials on living patients (for fear of spreading infections).

Note: All of the above drugs are usually delivered IV for euthanasia. That’s because Propofol can’t go IM and both Telazol and ketamine/valium sting when delivered in the muscle. Nonetheless, a brief sting is considered acceptable by many vets (indeed, I’ve done it when necessary out of safety). The biggest benefit of IV injection is the speed of action; most animals are deeply “asleep” within seconds.

Medetomidine: Marketed as Domitor by Pfizer, this drug is excellent to induce a pain-relieving sedation with a sting-less IM injection for dogs. Mixed with opiates and other drugs, it also works well for painless IM injection in cats. It’s price, however, leaves something to be desired. It’s pricey for big dogs.

Acepromazine: “Ace,” as it’s known, is a tranquilizer commonly used in vet practice to chill out aggressive dogs through IM injection. Though I much prefer to use small doses of Domitor mixed with opiates, Ace is popular for its inexpensiveness and low abuse potential. Some animals react to the sting of the needle when delivered IM, but it can definitely be included in IV preparations.

Xylazine: Lots of vets include this drug in their first injection cocktails. It’s most commonly used as a tranquilizer in horses but it’s great, inexpensive choice for overdosing small animals as part of the first injection.

Another note: none of these drugs causes an “awake” form of paralysis. Many owners fear this but, rest assured, we are not merely rendering animals motionless with our choice of first injection drugs. Nothing less than a profound sedation/anesthesia is the goal of this stage.

The final injection

Barbiturates: Almost all vets use barbiturate for this second injection. Many different preparations of barbiturates are used to overdose animals quickly. These are almost always given IV for rapid onset of cardiac arrest (within fifteen to sixty seconds in most cases).

Sometimes, however, if the first injection is extremely effective (as it is designed to be), an intraperitoneal (into the abdomen) or intracardiac (directly into the heart) injection is considered a humane alternative. This usually happens when the intravenous route becomes complicated by severe dehydration, shock, or some other process limiting ready access to the veins.

Note: Intracardiac injections of barbiturates are painful and should NEVER be administered to an animal that is not anesthetized or verifiably unconscious. An intraperitoneal injection of barbiturates in a conscious animal, however, is considered a humane method by some veterinarians’ standards. Indeed, I do not believe these injections are painful, but I do not opt for this method as it is lengthy as the animal slowly falls into a deep slumber. To me, it does not seem so predictable a process as the two injection method.

Is one injection enough?

Some vets still opt for the one injection method. If an animal is already unconscious or anesthetized I sometimes opt for it, too. As recently as five years ago, a majority of veterinarians was still using the one injection protocol and while it is still considered humane, the animals will often struggle and appear to resist. The two injection approach, by contrast, seems much more peaceful to most veterinarians and pet owners.

What if they move after the second injection?

Movement after death (such as an intake of breath) is not considered a sign of pain or incomplete euthanasia. It is common. In fact, some movement is typical. It happens because of electrical impulses remaining in the peripheral nerves of the body after brain waves have ceased.

Because less movement is seen if the animal is deeply sedated or anesthetized before the second injection is administered, and because humans are often disturbed to see movement after death (no matter how normal it is), this is another reason most of us now opt for two injections.

Is an IV catheter necessary?

Some vets require that an IV catheter be placed prior to euthanasia for added security. Doing so depends seems to depend primarily on the veterinarian’s comfort level giving IV injections. It does, however, ensure that things go more smoothly in most cases, but it is not strictly necessary. In fact, I tend not to use them because I know how much my own dogs HATE having IV catheters placed. Some vets will give the first shot and then pace an IV catheter. I prefer this approach as the animal doesn’t feel the catheter at this point.

Summing up

I know this is a long post and I know you’ll have more questions but euthanasia deserves nothing less than a complete discussion. It’s a difficult experience, emotionally, and I hope to help set your mind at ease about medical issues you may not know about or may have misgivings about. I hope this post will help you face your next experience with more comfort and less stress over the technical aspects of euthanasia you can't always control.