Please don't use horse dewormer! I own a horse and figure my problems started playing with a nasty, sickly barn kitten. :( A tube of horse dewormer is generally a 1200 lb dose. I haven't been able to locate how many mg of ivermectin is in the stuff per mg of paste!
What I used says "8 mg / ml" and is an alcohol suspension (sheep drench - NOT INJECTABLE!), which is suppose to increase the "availability" of ivermectin. It worked. The only side effect of it was feeling a bit warm and light headed about 4 hours post ingestion.
Google "ivermectin monograph", the first result contains dosages about half way down the page.
I religiously deworm my horse 4 times a year. Horses graze and continuously re-infect themselves so if you own one, you've gotta know your parasites! You'd think something like this couldn't happen to me because I'm also a wee bit OCD with the hand washing. :(