I am not trying to be disrespectful to anybody but a 10% solution (w/v) would be fatal to any known vertebrate. Merck doesnt even sell it in that high of a concentration. I am a molecular biologist but I am going to talk off of the cuff here so you might want to do your own reserach before applying Ivermectin.
Ivermectin is a neurotransmitter agonist. It is about as far from being benign as they come. Specifically it upregulates gamma amino butyric acid (GABA). GABA acts to block nerve impulses. In short, too much and your nervous systen stops, you slip into a coma and die.
10% solution is many, many times too concentrated. Abrahams (1992) reported in the "Bulletin of the Association of Reptile and Amphibian Veterinarians", that a 1:2000 dilution of a 5 microgram/milliliter stock solution was effective in treating mites. That final concentraion is something like 0.00005%. If I remember right you can buy it in a concentrated liquid topical solution of around 1% (1 mg/ml) It is meant to be diluted. That should be diluted 1:2000 for a final working topical solution.
One drop of a 1% solution was given to bats externally and proved fatal. A couple ounces of a 10% solution applied topically would likely kill a horse. Merck, the manufacturer warns specifically against using it on reptiles for any reason. It does work and I have used it successfully to treat ticks on wild caught blood pythons but be very, very careful with concentrations and how much you spray on the animal. I have also heard several anecdotal stories about the deliterious effects of Ivermectin on arboreals specifically.
Not just my opinion, it is all over the internet. I suggest you do your own homework.
Steve
