Hi,mi Child Just Had His Cast Removed From Braking His

Hi,mi Child just had his cast removed from braking his arm.
This past monday. On saturday je complainde of cronic pain on the arm. . Elbow area
We stoped by on monday te get the cast and pins removed. .
My wife notice one of thie pins had pus.. now he is secrating pus. And candt bend the arm.
Im in the emergency room they are thinking on a Ib. My question is can it be traded with drinkable. Medicine or it has to be IB. ? and dosent he need blode test first?