There is a lot of info on reefcentral about interceptor. Basically it is a medication used for cats and dogs to prevent heart worms. Interceptor works by stopping the heart of the heart worms. And it just so happens that red bugs and other similar crustaceans have a similar heart. If you treat with interceptor it can kill other crustaceans such as shrimps, crabs and amphipods but I know some people who were able to treat their tanks without losses. They did it by using just enough to kill the red bugs but not enough to affect the larger arthropods like cleaner shrimps. But if you really want to be safe you should remove all desirable arthropods and add the recommended dosage.
As for getting interceptor, it is usually a prescription only drug but you may be able to talk to your vet (if you have one) or a local vet about your problem.