Upon further reading it seems these mites exist on EVERYONE'S skin and just killing them only provides a temporary solution at best. This like many health conditions is a matter of improving the terrain rather than just killing the bugs which will only be replaced by more bugs. I liked gina's approach with boron better as I think it improves your terrain as well as killing the critters. I think the reason ivermectin worked to completely rid my son's doberman was that it was an acute condition on a puppy and once the ivermectin got the upper hand on the mites the puppy's natural defenses took over from there to control them.
Also I never addressed your question about the injection site. The medication works systemically so the injection site is irrelevant.