Help! What's Max Dose Penecilyn I Can Give Goat?

[blackie's maiden]

Around 175 lbs. Injured wrapping electric wire around one leg...took off most of skin, now infected. I gave him 3 ml today. Feed store recommended 1-2 ml for 7 days but is 7 days too long? Will I wind up with antibiotic-induced coocidiosis? 

Recommendations?