Yes you can give a dog Amoxicillin 500mg as long as they are heavy enough in weight.
Giving a smaller dog 500mg of Amoxicillin could kill them due to an overdose but as long as the dog weighs enough and is a larger dog then you can usually safely give the dog 500mg of Amoxicillin and they will be safe.
The recommended safe dosage of Amoxicillin for dogs is 5 to 10 mg of Amoxicillin per each lb the dog weighs.
The dosage of Amoxicillin for dogs should be given to the dog every 12 to 24 hours.
If your dog weighs 30 lbs then you can give them up to 300mg of Amoxicillin and if they weigh 40 lbs or above you can usually safely give the dog up to 500mg of Amoxicillin.
As long as the dog is a large dog then 500mg of Amoxicillin is considered safe every 12 to 24 hours.