A Retrospective Single-Centre Cohort Study Comparing Lower-Dose Intravenous Immune Globulin (IVIg) (1 g/kg) to Higher-Dose Ivig (2 g/kg) in Adult Immune Thrombocytopenia
Authors: Richards Mikhyla J , Wang Sophie Yu , Kim Ribeka , Chipperfield Kate M , Pi David , Chen Luke Y. C. 
Published: October 2019

Abstract
Abstract 3324

Background
Intravenous immune globulin (IVIg) is a standard first line treatment for immune thrombocytopenia (ITP). The optimal total dose for adults is not clear, and historically, many centers have used a total dose of 2 g/kg. However, the most recent evidence-based guidelines from ASH recommend an initial dose of 1g/kg, with an additional dose in cases with lack of response (Neunert et al, Blood, 2011). Based on this guideline, our tertiary care centre decreased the initial dose of IVIg in adults with severe ITP from 2 g/kg to 1 g/kg in June 2011.

Rationale
To date, there is no robust level I or II evidence to indicate the optimal dosing of IVIg in adult ITP. The objective of this study is to examine the effect of the change to 1 g/kg on clinical and laboratory outcomes at our centre.

Methods
All patients ≥18 years who received IVIg for ITP at our centre between April 2007 and June 2012 were identified. Patients who had received IVIg treatment within a year prior to the current course of therapy or treatment with concurrent platelet transfusions were excluded. Patients who received more than one treatment during the study period were included only once in the first episode in our analysis. The primary outcome was overall response, defined as a doubling of platelets within 7 days from before IVIg treatment to a minimum of ≥ 30 ×109/L. Secondary outcomes included peak platelet count achieved, average length of hospital stay, relapse, and requirement of rescue therapy within 30 days. Relapse was defined as loss of response (platelets < 30 × 109/L, bleeding or need for rescue therapy) after initial achievement of response within 90 days. Rescue therapy included subsequent platelet transfusion, steroids, repeat IVIg, anti-D, rituximab or splenectomy. Patient characteristics and outcomes were compared between the 2 g/kg and the 1g/kg group using Chi-squared analysis for categorical variables and 2-sided t-tests for continuous variables.

Results
75 patients were identified, of which 59 met the inclusion criteria. 45 of the included patients had been treated with higher dose IVIg (average of 2.01 g/kg) and 16 received a lower dose (average of 0.92 g/kg). The baseline characteristics between the two groups including age, gender, weight, secondary causes of ITP (drug-related: 13.3% vs. 0%, p = 0.295; viral-related: 17.8% vs. 25%, p = 0.798; autoimmune disease: 17.8% vs.6.3%, p = 0.482; hematological disorder: 6.7% vs. 6.3%, p = 0.595; other: 2.2% vs. 6.3% p = 0.979), duration of IVIg treatment (2.3 ± 0.13 days vs. 1.1± 0.06 days), and initial platelet count in both groups were similar at diagnosis. No significant differences were observed between patients in the higher-dose group and those in the lower-dose group with respect to: overall response rate (93% vs. 81%, p=0.18), peak platelet count (173 ± 19×109/L vs. 146 ± 39×109/L p=0.37), average length of hospital stay (3.6 ± 0.4 days vs. 4.5 ± 1.9 days p=0.47), relapse (60.0% vs. 43.8% p=0.38), and requirement of rescue therapy within 30 days (37.8% vs. 43.8% low-dose p=0.77). Furthermore, there were no significant differences observed in the probability of maintained response between the two groups.

Conclusion
These results suggest that adult patients diagnosed with ITP can be treated with an initial IVIg dose of 1g/kg with comparable outcomes to 2g/kg. A sufficiently powered randomized controlled trial is necessary to confirm these findings.

Disclosures:
No relevant conflicts of interest to declare.