This is an open-label, repeat-dose, multicenter extension trial of HZNP-HZN-825-301. Participants who complete the double-blind Treatment Period (Week 52) in Trial HZNP-HZN-825-301 will be eligible to enter this 52-week extension trial. Participants entering this extension trial will complete the Week 52 Visit activities in HZNP-HZN-825-301 and will not complete the Safety Follow-up Visit 4 weeks after the last dose of trial drug in HZNP-HZN-825-301.
Primary Objectives:~The primary efficacy objective is to assess the efficacy of 52 weeks of open-label treatment with HZN-825 in participants with diffuse cutaneous systemic sclerosis, as measured by change from both baselines in forced vital capacity percent (FVC %) predicted.~The primary safety objective is to examine the safety and tolerability of 52 weeks of open-label treatment with HZN-825, inclusive of, but not limited to, adverse events (AEs), serious AEs (SAEs) and the adverse event of special interest (AESI), from Day 1 to 4 weeks after last dose.