For most approved subcutaneously (SC) administered drug products in the US, the recommended injection sites (i.e., abdomen, thigh, and upper arm) are usually based on experience from phase 3 trials. Relative bioavailability data directly comparing the pharmacokinetics (PK) of different SC injection sites are often not available and the underlying mechanisms that may affect SC absorption have not been systematically investigated. In this study, we surveyed clinical PK data (AUC, Cmax, and Tmax) for SC administered drug products including therapeutic proteins and peptides based on literature and FDA database. The PK data after abdominal injection was used as a reference to determine the relative bioavailability of SC injections to the arm and thigh. The survey retrieved 19 immunoglobulin G (IgGs), 18 peptides/small proteins (molecular weight
