Biosimilar switching is evaluated using pharmaceutical, analytical, pharmacokinetic, and clinical comparability, whereas the act of self-injection introduces a separate set of device-dependent and user-dependent conditions. To explain when presentation changes might alter administration consistency despite acceptable biosimilar comparability, and identify observations capable of testing that explanation. This nonempirical multilevel theory integrates published work on biosimilar switching, patient experience, simulated-use human factors, injection mechanics, tissue deposition, and subcutaneous absorption. Four noninterchangeable quantities are distinguished: nominal prepared dose, drug expelled from the delivery system, drug deposited into the intended tissue compartment, and resulting systemic exposure. Formulation properties condition mechanical resistance; device architecture and user action jointly influence initiation, contact, injection completion, and removal; tissue geometry and local transport subsequently condition absorption. The account predicts that apparently equivalent use-task results may coexist with different mechanical or deposition outcomes, and that observed exposure differences may occur despite equivalent expelled mass. These are discriminating hypotheses, not demonstrated biosimilar-specific causal effects. Product-matched mechanical, behavioral, deposition, and pharmacokinetic comparisons are needed before clinical meaning can be assigned. Presentation evaluation should specify which stage of delivery is measured and preserve competing explanations across drug, device, user, and tissue levels.
IJPRAS
