Drug to put animal to sleep?

In general, no - most veterinarians use injectable euthanasia because it is more easily controlled and faster. The risk with a pill is that the dose is not sufficient to euthanize the animal rapidly, resulting in the animal suffering a long death or possibly not dying at all.

If you feel your dog should be humanely euthanized, you can call your veterinarian's office and ask what the cost of euthanasia is - the price can vary so call around. You can also check with your local animal shelter or humane organization - let them know this is a medical euthanasia (if that is accurate) rather than for your convenience and they may be able to provide free or low-cost euthanasia.