More and more biopharmaceutical and/or biotech companies begin to concern regulatory approval of biosimilar products, due to some innovator products will expire in decades. Once more biological products are going off patient, the problem whether approving biosimilar products used interchangeably and safely will be considered. Using a biological product of the reference product interchangeably, the United States Food and Drug Administration (FDA) requires that, for a biological product that is administered more than once to an individual, the risk in terms of safety or diminished efficacy of alternating or switching between the use of the biological product and the reference product, is not greater than the risk of using the reference product without such alternation or switch. For this purpose, based on the concept of switching and/or alternation several useful designs for assessing drug interchangeability are proposed. In addition, by developed biosimilarity index, a uni?ed approach is discussed. The proposed method is robust against biosimilarity criteria and is applicable under a valid and appropriate study design.