Background <p>Primary immune deficiency (PID) comprises over 400 inborn errors of immunity. Immune globulin replacement therapy (IGRT) is the standard of care for many PID subtypes. Intravenous immunoglobulin (IVIG) is the historic standard of care, but subcutaneous immunoglobulin (SCIG) offers several advantages for IGRT. Further, a novel pre-filled syringe (PFS) drug packaging form of SCIG is expected to facilitate more efficient patient infusions.</p> Objective <p>The aim of this study was to quantify the projected budget impact associated with adding the IgPro20 PFS as an SCIG drug packaging option to a health plan formulary for the treatment of PID.</p> Methods <p>A budget impact model (BIM) was developed across the United States (US) integrated delivery networks (IDNs)’ perspective over a 3-year time horizon to quantify the projected budget impact of adding the IgPro20 PFS as an SCIG packaging option for the treatment of PID. Model comparators included six IVIGs and seven SCIGs. A one-way sensitivity analysis was conducted to assess the impact of model parameters on the budget impact. Scenario analyses of alternative market share shifts and pricing were conducted to test the robustness of the model results.</p> Results <p>From the perspective of an IDN with 25 million members, the average annual expected cost per PID patient was US$73,343 for IgPro20 vials w/pump, US$60,892 for IgPro20 PFS w/pump, US$72,179 for IVIG, and US$96,581 for other SCIGs. Assuming market share uptake of 6.0% in the first year for IgPro20 PFS w/pump, rising to 8.4% by year 3, and offset by corresponding proportionate reductions in shares of the non-PFS SCIG IgPro20 vials w/pump only, the expected incremental budget impact over the 3-year horizon was savings of US$10.5&#xa0;million.</p> Conclusion <p>This BIM demonstrates that uptake of subcutaneous IgPro20 PFS is expected to be associated with substantial savings for a US IDN, including drug cost savings if offset by reduced non-PFS SCIG-packaging use.</p>