Need advice on what is the the emergency room treatment for a severe allergic reaction?

Many: For a severe allergic reaction there are many options that would probably all be given at once including: antihistamines, steroids, epinephrine. Other meds may be used depending upon the specific patient and the patients symptoms.

Several: Treatment for a severe allergic reaction (anaphylaxis) is Epinephrine injection, oxygen (if low pulse ox), intravenous fluids (for treating low blood pressure), antihistamines (h1 and h2) by injection or orally, albuterol by nebulizer (if asthma like symptoms), steroids (prednisone by mouth or solumedrol (methylprednisolone) iv), blood pressure support medications and rarely Methylene Blue (for refractory symptoms).