Clinical outcomes, patient perception and health economic impact of intravenous versus subcutaneous immunoglobulin treatment in primary and secondary immunodeficiency in Australia

Tanja Windegger

doi:10.25907/00016

Patients with primary immunodeficiency (PID) or secondary immunodeficiency (SID) due to haematological malignancy or its treatment often cannot produce sufficient functional immunoglobulin G (IgG) for protection from infections. These patients benefit from immunoglobulin replacement therapy (IRT), which is available in two administration modes in Australia. Intravenous immunoglobulin (IVIg) is administered monthly by a nurse in a hospital or outpatient setting, while subcutaneous immunoglobulin (SCIg) can be self-administered weekly by the patient at a place of convenience. There is substantial published evidence for use of IVIg and SCIg in PID cohorts. However, even though SID patients are one of the biggest immunoglobulin product user groups there is very little published data on their use of IVIg and SCIg. While SCIg has been available overseas for decades, its use in Australia was approved more recently in March 2013. Overseas reports indicate advantages with SCIg, however the uptake in Australia has been poor with less than 5% in 2015/16. To explore the poor SCIg uptake in Australia, the clinical outcomes, patient’s perception and cost-effectiveness of the two treatment modes in Australia were examined. Clinical and cost data from adult PID and SID patients were collected from hospital records and pathology reports. Data on patient’s satisfaction with the SCIg training program, information on side effects, management of side effects and patient perceived overall health and quality of life (QoL) impact were obtained via a study specific questionnaire and the Assessment of Quality of Life – 6 Dimensions (AQoL-6D) survey. For the clinical and patient perception component, PID and SID data were collected on the patient’s last 12 months of IVIg treatment and the following 12 months with SCIg. To gain a longitudinal perspective, SID patients were studied for a total of 36 months of SCIg treatment. A Markov cohort model was constructed to assess the health economic impact using a cost-utility analysis (TreeAge Pro Software). The clinical outcomes presented in Chapter 3 in both cohorts suggest that SCIg is an effective alternative to IVIg. Serum IgG levels were slightly elevated with SCIg compared to IVIg in PID (9.3 g/L vs 8.4 g/L) and SID (8.4 g/L vs 7.1 g/L) patients. The mean annual infection rate was comparable at 2.43 with IVIg and 1.79 with SCIg in the PID cohort, and 1.85 and 2.31 respectively in the SID cohort. Importantly the number of hospitalisations due to infection decreased in both cohorts with SCIg (PID from 0.29 to 0.14 and SID from 0.23 to 0.08). Due to the small cohort size (PID n=14; SID n=13) the study was not powered for statistical analysis. Results from the 36 months longitudinal study of SID patients (n=17) indicate that dosage, serum IgG levels and infection rate remained stable over time. However, the number of infections requiring hospitalisation fluctuated from 37% with IVIg to 9%, 15% and 32% with SCIg in year 1, 2 and 3 respectively. Despite the National Blood Authority’s (NBA) recommendations of IRT breaks in the SID cohort, none of our patients had a treatment break in the 48 months follow up. Interestingly, the number of SID patients remaining infection free appeared to increase over time from 15% with IVIg to 12%, 24% and 42% with SCIg in year 1, 2 and 3 respectively. SCIg was the preferred treatment mode in our cohort. Results from the project specific questionnaire showed that 91% of patients rated the SCIg training received as “very good”, with the mean number of training sessions required to self-administer being three. The side effects with IVIg and SCIg were similar. There appears to be a trend of fewer headaches with SCIg compared to IVIg. The infusion site reactions with SCIg, such as burning, swelling and redness, remained unchanged over the three years. However, patients reported the side effects as manageable and only few patients used medication to treat side effects. Separate cost-utility analyses were performed for the PID and SID cohort, due to differences in cost associated with treatment of infection, utility values, probability of developing an infection and mortality risk between the two cohorts. These differences were reflected in the results. SCIg was the dominant treatment options for both cohorts. The cost savings with SCIg treatment were less for the SID cohort ($8,082) compared to PID ($45,835) over a 10-year time horizon for the Australian health care sector. This appears to be the first published results comparing IVIg and SCIg using a cost-utility analysis. It is noteworthy that the Markov model created for this study was used by the Medical Services Advisory Committee (MSAC) in their 2019 report to advice the Australian Government on clinical efficacy, QoL and health economic outcome of IRT for SID patients. In summary, data from this study show that the clinical outcomes for IVIg and SCIg are comparable in PID and SID patients. SCIg was the preferred treatment mode by patients and SCIg treatment provides cost-savings for the Australian health care sector.

Clinical outcomes, patient perception and health economic impact of intravenous versus subcutaneous immunoglobulin treatment in primary and secondary immunodeficiency in Australia

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