The reason I use Interceptor over Heartgard Plus is because it comes in a dose for smaller dogs, like you mentioned (2-10 lbs), AND because it protects against roundworms, hookworms, and WHIPWORMS (Heartgard Plus doesn't protect against whipworms, which are difficult to detect and can be deadly!) That being said, and even though my preference is Interceptor (for the above reasons), I don't think it would hurt your furbabies to use the Heartgard Plus...and it makes me feel even better about it that you were told to give them each 1/2. I know lots and lots of people use Heartgard Plus with great results. (But truthfully, if it were me, I'd go back and get the Interceptor...it was their mistake, not yours! But I'm funny like that
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