anoki, I think you mean specifically Ivermectin paste? Ivermectin and pyrantel are the ingredients of Heartgard Plus. Ivermectin comes in several forms. I buy the Ivermec brand Ivermectin injectible wormer from the vet (or a friend with cattle) in a 10mL Syringe. I could have bought only one cc but I just got extra... I mix 100mL (cc) of propylene glycol (about $25 for a gallon) to 1mL of Ivermectin. THEN the dose is like this. I give 0.1mL of the new soultion per 10lbs. I use a diabetic syringe. I got the doseage from the vet who basically said here it is...I said nothing. The collie/shepherd breeds are not supposed to get ivermectin because there is a breakdown, in some dogs of these breeds, of their blood-brain barriers and too much ivermectin gets to theri brain and kills them. My vet said if I had given them the ivermectin and they were still alive, they did not have that problem. The saying is "White feet, don't treat" I have miniature australian shepherds and mini dachshunds. My friend breeds German Shepherd show dogs. She dilutes the ivermectin a 10th less...but she is dosing bigger dogs. No problems here...but I did not know when I started giving them the ivermectin that it could have been a problem.
I have heard people having their dogs overdose on ivermectin by eating horse poo after horses were treated. Not sure how true this is, but sounds plausible enough for me to ban the poo eating for 3 days after worming...I just let it go after that. I agree that the paste is virtually impossible to dose correctly. The liquid stuff tastes horrible (so the dogs say) and I guess that is why they wrap it up in $50 worth of yummy chewies, but they like the Strongid T (I get from the vet for horses and give 1mL per 5 lbs) so I give them the ivermectin first and wash it down with the pyrantel. My vet said that he would rather I wormed them like I am than not at all...he said he understands that with 15+/- dogs, Heartgard is cost prohibitive. It is not that it is wrong...it is just that A) the vets are supposed to sell the stuff to make money B) with improper doses, it can be a problem. My friend with mini doxies was very freaked out about the exact weight of her dogs and not overdosing. I looked at the packages of Heartgard and saw the wide weight range a package covered. So I asked the vet about it. They said that it was better to dose a little higher than a little lower...that is like guessing a dog is 12lbs and dosing for 15lbs vs. 10lbs. I also have the safe guard (the doseage for goats) and it is also 1mL per 5 lbs but for 3 days in a row. I have not had too much problems with fleas so have not worried about tapes (unless I see their evidence).
It is a little bit of money up front, but soooo much cheaper in the long run. I hope that helps. Oh and I have a bunch of friends with dogs and we all chip in an get the stuff to mix it. 100mL of ivermectin goes a long way at 0.1cc/10lbs even with the numbers I have!