The trial enrolled adults with definite or probable DM (Bohan & Peter criteria) and active disease and muscle weakness (MMT< 142/150). Subjects were randomized 1:1 to either high dose IVIG (2g/kg every 4 weeks) or placebo.

After week 16, eligible patients could enter the open label Extension Period, receiving 2 g/kg IVIg every 4 weeks for additional 24 weeks.

95 adult DM patients (∅ 53 years; 75% females) were enrolled. Overall, 96% and 73% patients completed the first and extension period, with 3 (3%) and 9 (10%) subjects discontinuing due to adverse events (1/3 and 6/9 related to IVIG), respectively.

Overall 664 infusions cycles were administered triggering 545 adverse events (AEs). 282 IVIG related AEs were reported in 62 (65%) subjects. Most related AEs were mild (73.4%), some moderate (23.4%) or severe (3.2%). Headache (42% of subjects), pyrexia (19%) and nausea (16%) were most common AEs. Premedication for IVIG infusions was required by 21.3% of patients.

IVIG-related serious AEs were reported in 7 subjects including thromboembolic events (TEE) in 5. By reducing the allowed maximum infusion rate from 0.12mL/kg/min to 0.04mL/kg/min the exposure-adjusted TEE incidence rate was efficiently lowered from 1.54 events/100 patient-months to 0.54.

The safety profile of IVIG administration even at high doses of 2 g/kg was consistent with commonly reported AEs for IVIG administration. Patients should be monitored for TEE (especially those with additional risk factors), if necessary, reduction of infusion rate be considered.

This first large, double-blind, placebo-controlled phase III trial demonstrated safety and tolerability of IVIG as a treatment for DM patients.