In rats, the Lethal dosage (LD50) which means 50% of the subjects were killed when administered this amount is 500mg/kg. A 2pound chicken weighs .9kg which means the lethal dose would be approximately 450mg.
Now when talking about treating animals with Benadryl; the most common is dogs and the accepted rate is up to 1 mg/lb every 8 hours (or 3 times a day -- tid). So if you have a 20 lb. dog, it's 20 mg of diphenhydramine. This is higher than the equivalent dose for humans, but nevertheless seems to be the accepted dose for dogs.
What the heck does this all mean? Effective dose appears to be 1mg per pound, lethal dose is 450mg. The first thread with a previous owner dealing with dosing benadryl used children's benadryl which is 12.5mg/5ml and she gave her 1ml, so 2.5mg total. Which is what I would suggest!
