Merck wins US FDA approval for first oral PCSK9 inhibitor

Edited by Robert McTiernan··3 min read

The US FDA approved Lipfendra (enlicitide), the first oral PCSK9 inhibitor, for adults with hypercholesterolemia including heterozygous familial hypercholesterolemia (HeFH), a milestone that resolves a longstanding formulation challenge in cardiovascular medicine. Merck (NYSE: MRK) developed enlicitide as a once-daily tablet, overcoming a formulation challenge that has constrained PCSK9 inhibition since the class emerged more than a decade ago with injectable monoclonal antibodies.

Lipfendra is approved as an adjunct to diet and exercise at a dose of 20 mg orally once daily. It is indicated broadly in adults with hypercholesterolemia, without a specific line-of-therapy restriction, though trial populations required additional LDL-C lowering despite stable statin therapy. Enlicitide is a macrocyclic peptide that binds directly to PCSK9, blocking its interaction with LDL receptors on hepatocytes — the same protein-protein interaction targeted by established injectable agents, now accessible through oral dosing. The approval does not yet extend to cardiovascular outcomes; an ongoing trial (CORALreef Outcomes, NCT06008756) is evaluating effects on morbidity and mortality, with results pending.

The approval rests on two Phase III trials from the CORALreef program. CORALreef Lipids (NCT05952856) enrolled 2,904 patients with hypercholesterolemia on background statin therapy, randomized 2:1 to enlicitide or placebo for 52 weeks. At the primary endpoint of mean percent change in LDL-C at week 24, enlicitide demonstrated a placebo-adjusted reduction of 56% (95% CI: −61, −51; p<0.001). CORALreef HeFH (NCT05952869) enrolled 303 patients with HeFH under similar conditions; enlicitide reduced LDL-C by 59% versus placebo at week 24. Both trials also reported statistically significant reductions in non-HDL-C and apolipoprotein B. The safety profile in CORALreef Lipids was broadly comparable to placebo; in CORALreef HeFH, diarrhea (7% vs. 2%) and dizziness (9% vs. 4%) occurred at higher frequencies with enlicitide. If positive, CORALreef Outcomes could support an expanded indication for cardiovascular risk reduction similar to those held by injectable PCSK9 inhibitors.

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Achieving oral bioavailability for a PCSK9 inhibitor required moving beyond conventional antibody or small-molecule formats. Enlicitide’s macrocyclic peptide structure confers conformational rigidity that enables high-affinity target binding while resisting proteolytic degradation in the gastrointestinal tract — a property that small linear peptides lack. Merck identified the initial hit using mRNA display technology and developed a biocatalytic synthesis route, published in Science, to support large-scale manufacturing. The approval validates macrocyclic peptides as an orally deliverable modality for targets previously considered intractable by mouth, a point underscored by Novartis’s subsequent USD 1.8 billion deal with Unnatural Products targeting cardiovascular disease using the same platform approach.

The PCSK9 inhibitor landscape enlicitide enters is already populated but predominantly injectable. Amgen’s evolocumab (Repatha) and Sanofi/Regeneron’s alirocumab (Praluent) — both subcutaneous monoclonal antibodies approved in 2015 — remain widely prescribed, yet adherence at the population level has been limited partly by route of administration. LIB Therapeutics’ lerodalcibep (Lerochol), an adnectin-based subcutaneous agent approved in December 2025, extended the injectable class with monthly dosing. Enlicitide’s once-daily oral format distinguishes it from all currently approved PCSK9 inhibitors, though whether that convenience translates to sustained adherence in practice remains to be demonstrated in real-world settings. Further out, gene-silencing and epigenetic approaches targeting PCSK9 are entering early clinical development, representing a next generation of competitors with potentially durable, infrequent dosing profiles.

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