I agree Lysine would be better for what you are trying to achieve. And I applaud you for trying to give them some love and care! Try to get them fixed if you can.
Fish mox dose is 10-20 mg/kg (5-10 mg per lb) twice daily
Fish cillin dose is 20-40 mg/Kg (9-18 mg/lb) every 8 hours orally.
Fish Cillin (Ampicillin) & Fish mox (Amoxicillin) are commonly given off-label to small animals.
Clinical use includes urinary tract infections, pneumonia and skin...
