I recommend ivermectin to many of my clients with multiple big dogs, but only if I think the client is responsible enough to measure out the right dose. If you have more than one greater than 50 pound dog the cost of Heartgard or Intercepter is painful, and for me having to buy them in cartons of 10 (as is required) is crippling. I carry Iverhart in my clinic because it’s the cheapest packaged heartworm prevention I have found.
Yes, I worked for a vet years ago and people do lots of goofy things. One client injected something a breeder had given her in a syringe (I don’t recall what it was now, it wasn’t ivermectin, but it was supposed to be given orally and the client had to find a needle to put on the syringe in order to inject it!).
I don’t have a problem affording preventative at this stage in my life, especially for one or two dogs —it IS expensive but I spent about $500 last time I was in the vet for my dog’s yearly visit including her vaccs and a cyst the vet wanted to look at so the heartworm meds were the least of my problems. :) Besides I’m far more irritated by the 75$ a year licensing fee I pay out here. I don’t feel like I get anything for that except annoyed.
For the collies and such, the preventative is USUALLY ok, but the deworming dose is way too high, and they will be seriously affected.
For those who use the paste, DON'T. You have no way of accurately measuring, and it will cause considerable damage, if not death.
On the heartgard package, divide the amount of active ingredient by the weight of the highest pound dog on the package, and that is your highest safe dose per pound you can use of the injectable. Be warned, the injectable is in milligrams per cc, not micrograms, so a small mistake is a 1000 X overdose.
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If you are not good with numbers (not willing to bet your dog's life on your mathematical genious)ask you vet to calculate the correct dose for your dog. If they won't do it, ask them why?
Most are not greedy. They just don't want to be resposible for your dog dying when you screw up your calculations.