Does Omnicef And Amoxicillin Contain Any Of The Same Ingredients?

does omnicef and amoxicillin contain any of the same ingredients? my son recently became allergic to omnicef and the doctor didnt want to give him amoxicillin afterwards before finding out if they contain any of the same ingredients. i just would like to know if it is safe for him to take amoxicillin or since hes allergic to omnicef its off the table to take as well. also if hes allergic to omnicef does that mean he cant take any cephalosporins like keflex?