The Subcutaneous Injection Site

To provide a framework to examine potential PK, PD, and metabolism issues for a protein or peptide administered by SC injection, it is important to appreciate the architecture of this site and some of the events that occur because of accessing this site. The physical, chemical, and biological characteristics of the SC injection site can provide a more or less hostile environment depending on the nature of the injected protein or peptide therapeutic. Because the SC injection site environment will change over time through tissue repair events initiated by the trauma produced by an injection, the SC injection site should be considered dynamic. Further, the nature of injected materials (including formulation elements) and their residence time at an injection site will potentially affect these dynamic SC injection site events. Thus, the use of a needle to access the SC space, the elements within the SC space that are resident and/or drawn to this site as a result of the injection, and the time course of clearance from injected materials from the SC site could all potentially alter PK, PD, and metabolic outcomes for an injected protein or peptide therapeutic.

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