First, thanks for the good info and links. Years ago, I found info online from Mississippi State regarding dosages of a lot of things, but I lost it, so I came here trying to get the right amount again. I recalled the dosage in water being very low but not exactly how low. I guessed and used 1/4 tsp of a pack of Prohibit soluble drench power, which is near double the amount I eventually found again this morning on a copy of the medications flyer I had printed years ago. It said to use .5g/gallon water, which comes out to about an 8th teaspoon at the weight per teaspoon given here. I'm happy to say that none of the chickens died that I overdosed: They were Silkies, Polkies (Silkie x Polish) including juveniles, juvenile French and Cuckoo Marans, a Barred Rock, Australorp, Sex-link, and game hen EE. I moved out all the remaining water this morning after I finally figured out the correct dosage. I'm reviving this old thread in case anyone else comes looking for an answer, and for myself the next time I lose the dosage in water. I didn't want to use Ivermectin again after I saw a chicken poop out a big wad of live roundworms a few days after I applied the cattle drench version. A study I read said Ivermectin doesn't do a good job of killing roundworms in chickens anway, so Levamisole is now in my rotation along with Valbazen (which I don't use during molt due to possibility of deformed feathers), Moxidectin, and eventually water-soluble Safeguard with no egg withdrawal. It's still more expensive than Moxidectin but maybe that will change. My farm is on 4th generation farmland with springs and lowland, on a slope, in Florida, so we get frequent downpours that turn runs into mud-baths. There's no chance we'll ever eliminate parasites from the ground even with torching, which we tried, and big dumpload trucks of sand we bring in to replace the dirt that washes downhill, often before I even find time to shovel out the old stuff. So I deworm adults every other month and chicks once a month up through laying age to keep the damage to a minimum. I often wonder why I keep trying, but I'm too addicted to chickens to give up.
I am a bit nervous using it until I know more. I will take a look at this link you provided here. 
