As a future vet, I say that idea sounds horrendous. Not to mention, that with any such drug on the market, such a claim is absolutely bogus.

The best way to prolong a dog's life? Correct diet, plenty of exercise, lots of socialisation... need I go on??

Yes, sometimes our pets are subject to disease and disability, and their lives are cut short. Yes, that's horribly unfair. But it is our job, as responsible owners, to care for them as best we can until their suffering becomes too great, and then it is our duty to put their needs before our own.

ETA: pomtzu, I did the same!