Thanks for your question, my name isXXXXX and hopefully I can be of some assistance.
Assuming the drug was prescribed for your dog previously, the dose for Penicillin VK for an 80 lb. dog is as follows:
Penicillin V 250mg - 1 tablet by mouth twice daily with food.
Any inappetance, vomiting or diarrhea, stop the medication immediately and call your veterinarian.
I hope this answer was helpful.
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