perhaps get a second opinion, if youve done this, then I wouldn't have a fucking clue how much of this or that would work.. I dare say it pends on the quality of the H, for instance, most places I here is around 10-20% street.. I think you could find via toxicology info data, and work out the weight of the sick dog, to get a gauge..Personally, Id get a qualified vet to do it, and if hes old and sick as stated, then this shouldn't be a drama.. I have heard of dogs getting put down, due to the owners getting sick, and not able to look after, I cant see the problem with a vet being able to do it.. see my interest in chem is theoretical ie learning the reactions only, and sometimes this is not the case in REAL world effects...find another vet