It is only effective in getting rid of them in the adult stage of life. However, it is not effective in guarding them against passing it on to other dogs or from the effects of the worms during their non-adult phases of life. These complications and the ability to pass them onto other animals, including humans, can begin very early in pups. I seriously doubt it is a good idea to begin a pup on heartworm medication at 2-3 weeks of age.
Just because Interceptor treats and prevents adult worms in dogs, doesn't mean they can't still carry and pass on the eggs an larvae, thus spreading infestation. (Heartworms can't be passed by means of feces...the worms' full life cycle is within the heart/blood stream.) So no, it is NOT an effective preventative. |