Inhibition of FcRn with rozanolixizumab in adults with immune thrombocytopenia: Two randomised, double-blind, placebo-controlled phase 3 studies and their open-label extension.

Primary immune thrombocytopenia (ITP) is an antiplatelet-antibody-mediated disorder with accelerated platelet clearance and decreased platelet production. Rozanolixizumab, a monoclonal IgG4 anti-FcRn antibody, blocks IgG recycling and decreases IgG levels. We report efficacy and safety of rozanolixizumab in adults with persistent/chronic ITP in 24-week phase 3 studies (TP0003; TP0006), and their 52-week open-label extension (OLE). Primary end-point was durable clinically meaningful platelet response (DCMPR) of ≥50 × 10⁹/L for 8/12 weeks during Weeks 13-25 in the double-blind studies. Operational delays and evolving ITP treatment landscape led the sponsor to terminate these studies early; thus, only 21 and 12 (TP0003) and 20 and 10 (TP0006) patients were randomised to rozanolixizumab or placebo. Forty-three patients enrolled in the OLE: 42 started on every 2-week dosing; 21 later switched to weekly dosing. More rozanolixizumab-treated than placebo-treated patients achieved DCMPR: 4/21 versus 0 (TP0003) and 1/20 versus 0 (TP0006). Platelet increases to ≥50 × 10⁹/L were observed on Day 8 in 52.4% (TP0003; 2/12 placebo) and 45.0% (TP0006; 1/10 placebo) of rozanolixizumab-treated patients. OLE platelet increases were maintained while on weekly dosing. The most frequent treatment-emergent adverse events overall were headache, pyrexia and nausea, as seen previously. Weekly dosing appears more efficacious than every 2-week dosing.