I don't know how you would use the pad since it's a deep wound. Did you rinse the wound out with saline? then the ointment.
Amoxicillin can be ordered online https://allbirdproducts.com/products/baytril-10 I bet they have Amoxicillin also. @Wyorp Rock may know if the antibiotic you have there is...
You've been given great info. if at all possible I would seek out vet help. With a wound like that just as @shawluvsbirds an antibiotic and vet care is very much needed. I hope he pulls through and you can keep this from happening again to him or any of your other ducks. Also there is great info...