I'm a little confused by your post but prednisone is an anti-inflammatory medication that is often prescribed to help ease the swelling and itching that come with a severe allergic reaction. Typically you take taper it - taking a high dose for a few days and then decreasing the amount you take each day for several days.
80 mg is a fairly high initial dose and may be just a single dose designed to help counter the allergic reaction.
If I read your post correctly you had an allergic reaction to penicillin so the prednisone is being prescribed to help minimize the reaction.
