I think the whole #ivermectin is primarily about business - cleverly stimulated demand, based on "counter-cultural" mythology, just as with #homeopathy, and other alt-med like all kind of "miracle" cancer drugs. Just look at these prices - and dozens of shops can be found online:
When I kept horses in 2000's I was using ivermectin periodically so I fully sympathize. Funny thing, I was using Bayer's pour-on ivermectin (a rather large bottle) which was not certified for use with horses (at least back then), but that was due to retention times in body (that did matter only for horses bred for meat).