Arrowhead Hits the Mark in FCS Treatment with REDEMPLO Approval—Now Comes the Ionis Challenge

Arrowhead Pharmaceuticals has reached a transformational milestone with the FDA’s approval of REDEMPLO (plozasiran) on November 18, 2025—marking the company’s first FDA-approved medicine and the first-ever FDA-approved siRNA therapeutic for familial chylomicronemia syndrome (FCS) treatment. This historic approval represents not only a pivotal achievement for Arrowhead but also a breakthrough for the estimated 6,500 Americans living with this severe and rare genetic metabolic disorder.

Familial chylomicronemia syndrome is a devastating, rare disease characterized by triglyceride levels that reach 10 to 100 times higher than normal, typically exceeding 880 mg/dL. According to DelveInsight’s analysis, the US reported approximately 1,400 diagnosed prevalent cases of FCS in 2023, a figure projected to rise significantly from 2025 to 2034. REDEMPLO uses an innovative approach that leverages small interfering RNA (siRNA) technology to target and suppress apolipoprotein C-III production. This liver-produced protein raises triglyceride levels by slowing their breakdown and clearance. By inducing sustained silencing of this target protein, REDEMPLO delivers significant and durable reductions in triglyceride levels—addressing the root cause of the disease rather than merely treating symptoms.​

The therapeutic leverages Arrowhead’s proprietary Targeted RNAi Molecule (TRiM) platform, which represents a differentiated approach to RNA interference therapy. This platform is particularly notable because it has demonstrated the potential to deliver siRNA to seven different cell types in the body and can silence the expression of two genes with a single molecule, expanding the range of diseases Arrowhead may be able to address.

The FDA recognized REDEMPLO’s significance by granting the therapy Breakthrough Therapy Designation, Fast Track Designation, and Orphan Drug Designation for FCS treatment. Additionally, the European Medicines Agency has granted Orphan Medicinal Product Designation, positioning the drug for potential international expansion.

REDEMPLO’s FDA approval is grounded in compelling efficacy data from the Phase 3 PALISADE study, a randomized, double-blind, placebo-controlled trial conducted across 39 sites in 18 countries with 75 subjects. The study met its primary endpoint and all multiplicity-controlled key secondary endpoints, demonstrating the drug’s remarkable effectiveness.​

The results were striking: patients receiving the 25-mg dose of REDEMPLO achieved a median reduction in triglycerides of 80% from baseline, compared to just 17% in the pooled placebo group. Beyond triglyceride reduction, the drug also significantly lowered apolipoprotein C-III (APOC3) levels, a key regulator of triglyceride metabolism. Perhaps most importantly for patients facing the constant threat of pancreatitis, the treatment group had a lower incidence of acute pancreatitis than the placebo.​

These data were simultaneously published in prestigious medical journals, The New England Journal of Medicine and Circulation, following presentations at the 2024 European Society of Cardiology Congress and the American Heart Association Scientific Sessions, lending significant credibility to the findings.

The safety data from PALISADE demonstrate that REDEMPLO is generally well-tolerated. The most common adverse reactions (occurring in ≥10% of patients and >5% more frequently than placebo) are hyperglycemia, headache, nausea, and injection site reactions. Notably, the FDA-approved package insert lists no contraindications, warnings, or precautions for REDEMPLO use, reflecting a favorable safety profile.

A major advantage of REDEMPLO is its convenient subcutaneous injection, administered once every three months at home, eliminating the need for frequent medical visits and improving FCS treatment adherence. This patient-friendly administration schedule represents a significant improvement in quality of life for individuals managing a chronic disease with complex treatment requirements.

Arrowhead has set REDEMPLO’s annual price at $60,000, and executives have committed to a pricing model that sets a single price across current and future indications. This pricing strategy reflects the company’s commitment to value while ensuring sustainable commercialization of this rare disease therapy. To further improve patient access, Arrowhead is launching “Rely On REDEMPLO,” a comprehensive patient support program that provides services, resources, and financial assistance to eligible patients.

REDEMPLO enters a market that’s no longer untested, thanks to the US approval last year of Ionis’ RNA-targeted ligand-conjugated antisense therapy TRYNGOLZA (olezarsen), the first FCS medicine specifically cleared in the country.

The launch of Tryngolza also represents a milestone for Ionis: after more than 35 years in business, it is the first time the company has commercialized one of its own approved drugs rather than licensing it to a partner. Ionis reported $32 million in TRYNGOLZA sales for the third quarter and expects full-year 2025 revenues of $85–95 million.

Even ahead of REDEMPLO’s approval, Arrowhead and Ionis were already locked in a legal battle. In September, both companies filed competing lawsuits. Ionis claimed Arrowhead had copied its patented mRNA technology to develop REDEMPLO and sought unspecified damages in a California court. Arrowhead countered that the disputed Ionis patent is “invalid and not infringed” by its planned commercialization of REDEMPLO. Both companies’ FCS therapies target the same pathway: reducing APOC-3 protein production.

The REDEMPLO approval for FCS treatment comes at a particularly significant moment for Arrowhead, following a challenging period related to the company’s partnership with gene therapy maker Sarepta Therapeutics. Last November, Arrowhead licensed multiple clinical and preclinical siRNA programs to Sarepta in a landmark $825 million upfront deal with potential additional payments reaching $10 billion based on clinical milestones. 

However, when Sarepta announced a safety-related strategic restructuring involving its gene therapy ELEVIDYS during the summer of 2025, Arrowhead’s stock declined 12% over approximately one month as investors questioned Sarepta’s execution capabilities. REDEMPLO’s FDA approval, combined with increasing stability in the Sarepta partnership, represents a significant turning point for Arrowhead’s stock and investor confidence. 

“With its first FDA approval in the books, and some stability on the Sarepta front with an updated label for ELEVIDYS, the winds appear to be blowing in the right direction for Arrowhead.”

While REDEMPLO’s approval for FCS treatment represents a landmark achievement, the drug’s clinical development extends beyond this rare disease indication. Plozasiran is currently being investigated in the SHASTA-3, SHASTA-4, and SHASTA-5 Phase 3 studies for severe hypertriglyceridemia and the MUIR Phase 3 study for mixed hyperlipidemia. These ongoing REDEMPLO trials suggest that the drug’s triglyceride-reducing capabilities may benefit a broader population of patients with less severe but more common lipid disorders.

REDEMPLO is expected to be available in the United States before the end of 2025, providing long-awaited therapeutic hope to the FCS community. For Arrowhead Pharmaceuticals, this approval marks not just a commercial milestone but a validation of its scientific platform and commitment to developing innovative treatments for serious diseases. As the company transitions into commercial-stage operations with its first approved medicine, the success of REDEMPLO will be closely monitored by both the investment community and patients who desperately need effective treatments for rare metabolic disorders.