I totally understand your confusion... I spent a month reading everything I could so that I could understand......and yes, there are several different beliefs on the topic..and the truth is that none are absolutely wrong. Those that extend the Ivomec are reducing its level of active product but still based on the dosage given in the name brand heartworm preventatives, they are within range.... those who do not use extender are not overdosing their dogs, they are indeed giving a larger portion of active ingredient but fortunately due to the nature of the active ingredient, there is a large error for margin so to speak.... I know I am not clearing things up for you more, but all the different opinions you have read are all correct and within range for providing the coverage necessary.

Originally, the vets that would recommend the Ivomec to pet owners were those located very rurally and prescribed it for both price point and higher level of coverage due to the fact that most dogs in those regions were in a higher level of exposure due to their lifestyles.... of the research I have done, most of the vets who prescribed and approved the use of the product recommended the un-extended product at .10 cc /10 lbs body weight. You can also find info on the Merck website that substantiates these recommendations.... those using extenders are still administering dosage capable of protecting their animals , it is just that the higher dosage is also within safe margins.....

You will hear those who swear by either one way or the other so for my own sanity and understanding, I spent the time checking with the 'experts'..... have you posed the question to your own vet? Mine personally does not condone the use of Ivomec..... but her main reasoning was that not everyone was capable of calculating the formulas correctly.... so in good conscience, she felt it best not to suggest or pass along any specifics.....suffice it to say, she did say that the same active ingredient as the name brands so it was not harmful if used correctly.

Good luck in seeking your answers... I am sure many others will follow me with their experiences.

Refer to a post by Zensojourner "Ivermectin for doggies" on this forum will give you correct and easy to understand info on what you want to know.