<p dir="ltr">Subcutaneous injection for self-administration of biotherapeutics, such as monoclonal antibodies (mAbs), is becoming increasingly prominent within the pharmaceutical sector due to its benefits in patient compliance and cost-effectiveness. The success of this drug delivery process depends on the coupled mechanical and transport phenomena within the subcutaneous tissue, both during and after the injection. Yet, the details of these processes are not well-elucidated, sparking a surge in computational efforts to fill this knowledge gap. Remarkably, there are very few computational studies on subcutaneous injection into three-dimensional porous media that account for large tissue deformations, drug transport and absorption, the use medical devices, and human factors. Here, we develop a high-fidelity computational framework to study large-volume subcutaneous injection of mAbs. Our investigation begins with a linear poroelastic model without drug transport, which we employ to study the effect of tissue deformation on injection dynamics. We progressively enhance this model, advancing to a nonlinear porohyperelastic framework that include drug transport and absorption. To capture the anisotropy of subcutaneous tissue, we employ a fibril-reinforced porohyperelastic model. Furthermore, we integrate the multi-layered structure of skin tissue by creating data-driven geometrical models of the tissue layers derived from histological data. Our analysis explores the impact of different handheld autoinjectors on the injection dynamics for various patient-applied forces. We investigate the effect of different pre-injection techniques, such as the pinch and stretch methods, on the drug transport and absorption. Additionally, we evaluate the impact of several physiological variables, including flow rate, injection depth, and body mass index. Our simulations yield crucial insights essential for comprehending and improving subcutaneous drug administration of mAbs. Additionally, they offer a deeper understanding of the human aspect of the injection procedure, thereby paving the way for advancements in the development of patient-centered injection devices and techniques.</p>