H1 antagonists with low sedating activity, such as fexofenadine, loratadine, cetirizine, are preferred over diphenhydramine and hydroxyzine when appropriate
Improves urticaria but not angioedema at 2 hours
Continue steroid burst if outpatient (40mg prednisone PO x 5 days)
Acute allergic reaction
Allergic reaction/urticaria
Contrast induced allergic reaction
Anaphylaxis
Acute asthma exacerbation
Angioedema
Acute asthma exacerbation 
Anxiety attack