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Differences in Patient Demographics and Healthcare Costs of Patients with PIDD Receiving Intravenous or Subcutaneous Immunoglobulin Therapies in the United States.

Background
Primary immune-deficiency disease (PIDD) is a rare, debilitating disease of the immune system that predisposes the affected individual to infection, autoimmune conditions, and neoplasm. A major component of the cost of treating PIDD is the high price of immunoglobulin drugs, which can be administered via an intravenous (IV) or subcutaneous (SC) route.


Objective
To compare real-world costs for patients with PIDD who are receiving IV immunoglobulin (IVIG) or SC immunoglobulin (SCIG) treatment, from a US payer perspective, using a large claims database.


Methods
Based on 2011 to 2013 data from the PharMetrics Plus database, a large national healthcare claims database, patients who were newly diagnosed with PIDD were included in the study if they had ≥2 claims for PIDD that were ≥90 days apart, and if they were treatment-naïve for a minimum of 1 year before the study period. Patients who switched the route of immunoglobulin administration were excluded, with the exception of patients who received SCIG who could initially receive ≤2 IV-loading infusions, as directed by treatment guidelines. We used propensity score analysis to match the patients in the SCIG cohort to patients in the IVIG cohort based on age, sex, and all Elixhauser comorbidities. We compared the patient characteristics and direct medical costs (all-cause, PIDD-related, and pharmacy-related) before and after matching, using t-tests for continuous variables, chi-square test for categorical variables, and Wilcoxon rank-sum test for differences in medians.


Results
A total of 1639 patients with PIDD (986 who received IVIG and 653 who received SCIG) met all the study inclusion criteria. Compared with the patients who received IVIG, the patients who received SCIG were predominantly female (58% vs 63%, respectively) and significantly younger (mean age, 49.1 vs 40.3 years, respectively). Significantly fewer patients who received SCIG than those receiving IVIG had claims with International Classification of Diseases, Ninth Revision codes for Elixhauser comorbidities, including cardiovascular and pulmonary conditions, diabetes, renal failure, liver disease, cancers, weight loss, fluid and electrolyte disorders, and psychoses (P <.05 for all), and their Charlson Comorbidity Index scores were lower than those receiving IVIG (1.74 vs 3.01, respectively; P ≤.05 for all). After matching the 2 cohorts (N = 553 in each), the 1-year postindex median total PIDD-related costs were significantly lower in the IVIG group than in the SCIG group ($38,064 vs $43,266, respectively; P = .002).


Conclusions
In matched analyses, PIDD-related treatment costs were higher for patients who received SCIG than for those who received IVIG. Furthermore, patients who received SCIG were significantly younger and had significantly less comorbidities than their counterparts who received IVIG, suggesting that patient characteristics that reflect a desire and greater capacity for autonomy may affect physicians' choice of the route of administration for immunoglobulin.