This patient most likely has anaphylaxis. Epinephrine (adrenaline) is the mainstay treatment for anaphylaxis because of its fast action. Epinephrine should be given intramuscularly; the usual site for injection is the mid-anterolateral thigh. Intravenous epinephrine is reserved for severe anaphylaxis and hypotension that does not respond to intramuscular epinephrine. Corticosteroids act too slowly to be of help in severe, acute anaphylaxis, especially oral prednisone. Methylprednisolone may be given intravenously, depending on etiology, but not before IM epinephrine.