Welcome to Healthcare Magic Since he has developed allergic reaction Benadryl will remove the hives and any other associated features. In case he has respiratory difficulty it would be best to get him to the ER because steroids may become necessary to control the allergic effects. Keep in mind that he may be allergic to all penicillins like Cephalosporins, Ampicillin, Penicillin as well. Tell his Doctor that he has this allergy. Give him good rest. Avoid sun exposure. Apply lactocalamine on the hives if itching is much. He needs to drink plenty of water. Follow up with his Doctor after that.