My book, "Plumb's Veterinary Drug Handbook" has two listings for amoxicillin:
125mg/kg every 12 hours
100mg/kg every 8 hours
I think you said you have the 400mg/5ml, so that means that there are 80mg per 1 ml or 8mg per 1/10ml.
1kg = 2.2 pounds
1ml = 1cc
-Kathy