Enlicitide

Merck's MK-0616, an oral macrocyclic peptide that blocks PCSK9 binding to the LDL receptor, approved by the FDA on July 15, 2026 as Lipfendra for LDL-cholesterol lowering after the CORALreef phase 3 trials showed roughly 56 to 60% placebo-adjusted reductions.

Also referenced as: MK-0616, enlicitide decanoate, enlicitide chloride, Lipfendra

Also appears in: Metabolic

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What is Enlicitide?

Enlicitide, developed by Merck as MK-0616, is a synthetic macrocyclic peptide that binds PCSK9 (proprotein convertase subtilisin/kexin type 9) and prevents it from binding the LDL receptor. It is a heavily engineered bicyclic structure rather than a linear chain of natural amino acids: eight residues, six of them non-canonical, built around a 37-membered ring. The discovery team started from hits found by mRNA display screening, then rebuilt the molecule with structure-based design, an olefin cross-link closed by ring-closing metathesis and a quaternary trimethylammonium tail to reach picomolar potency with enough stability to survive the gut (Johns et al., Circulation, 2023;148(2):144–158; Josien et al., Journal of Medicinal Chemistry, 2026;69(11):13473–13491). Because the active molecule is a cation, it is supplied as a salt: the chloride was used in the phase 2b trial and carries the INN, while the decanoate is the USAN form in the marketed tablet, with a molecular formula of C92H129FN14O17 and a molecular weight of 1,722 Da.

It matters because it is the first orally dosed PCSK9 inhibitor, offering the LDL-cholesterol lowering previously available only from injected antibodies or siRNA. It is approved as Lipfendra for adults with hypercholesterolemia, including heterozygous familial hypercholesterolemia. It has essentially no footprint in the research-peptide market.

How it works

• Blocks the PCSK9–LDL receptor interaction. PCSK9 binds LDL receptors on hepatocytes and routes them to lysosomal degradation instead of recycling. Enlicitide binds PCSK9 with a Ki of about 5 pM and sterically prevents receptor binding, so more receptors return to the cell surface and clear LDL particles from plasma; the FDA label describes the mechanism in the same terms (Johns et al., Circulation, 2023;148(2):144–158).
• Free PCSK9 suppression. In the first-in-human study, single doses produced a greater than 93% geometric mean reduction in free, unbound plasma PCSK9, and 14 days of once-daily 20 mg dosing in statin-treated participants lowered LDL-cholesterol by up to 61% from baseline (Johns et al., Circulation, 2023;148(2):144–158). The label notes that single doses of 10 mg or more drive free PCSK9 down by more than 90% at peak concentration, reached 30 to 60 minutes after dosing.
• Oral absorption. Macrocyclic peptides are normally too large and polar to cross the intestinal wall. The Merck series was optimized for potency, permeability and metabolic stability until lead compounds maintained therapeutic exposure in rats and cynomolgus monkeys when given with an enabling formulation (Tucker et al., Journal of Medicinal Chemistry, 2021;64(22):16770–16800). The approved tablet co-formulates enlicitide decanoate with sodium caprate; even so, oral bioavailability is only about 1%, plasma exposure is less than dose-proportional, and the molecule is minimally metabolized and eliminated mainly by glomerular filtration, with very low cytochrome P450 and transporter interaction potential in vitro and no clinically meaningful drug interactions observed in the label’s studies.
• Downstream lipoprotein effects. Beyond LDL-cholesterol, the HeFH phase 3 trial recorded placebo-adjusted reductions of 49.1% in apolipoprotein B, 53.0% in non-HDL cholesterol and a 27.5% median reduction in lipoprotein(a) at week 24, the same pattern seen with evolocumab and alirocumab (Ballantyne et al., JAMA, 2026;335(2):129–139).

Research status

Discovery and phase 1. Merck’s PCSK9 macrocycle program synthesized thousands of analogs before settling on MK-0616, which emerged from an issue-driven, fragment-based redesign of earlier bi- and tricyclic leads (Josien et al., Journal of Medicinal Chemistry, 2026;69(11):13473–13491). The Circulation paper that introduced the compound reported two phase 1 studies in healthy adults: a single rising-dose trial establishing safety and PCSK9 suppression, and a 14-day multiple-dose trial in participants on statins (Johns et al., Circulation, 2023;148(2):144–158). Two further chemistry papers describe a convergent total synthesis (Li et al., Journal of the American Chemical Society, 2025;147(13):11036–11048) and a biocatalytic manufacturing route that uses engineered enzymes for fragment coupling and macrocyclization, cutting the step count by more than half (Klapars et al., Science, 2026;392(6798):643–647).

Phase 2b (NCT05261126). A double-blind trial at 63 sites randomized 381 adults with hypercholesterolemia equally to placebo or MK-0616 6, 12, 18 or 30 mg once daily for 8 weeks. Placebo-adjusted LDL-cholesterol reductions were 41.2, 55.7, 59.1 and 60.9% respectively, all with p less than 0.001, with adverse events in 39.5 to 43.4% of treated participants versus 44.0% on placebo and no more than two discontinuations for adverse events in any arm (Ballantyne et al., Journal of the American College of Cardiology, 2023;81(16):1553–1564). A 20 mg dose was carried into phase 3.

CORALreef Lipids (NCT05952856). The pivotal trial enrolled 2,912 adults with a prior major atherosclerotic cardiovascular event and LDL-cholesterol of 55 mg/dL or higher, or at risk of a first event with LDL-cholesterol of 70 mg/dL or higher, randomized 2:1 to enlicitide 20 mg or placebo once daily for 52 weeks; 2,909 formed the intention-to-treat population. Mean baseline LDL-cholesterol was 96 mg/dL and 97% of participants were on a statin. At week 24, LDL-cholesterol fell 57.1% with enlicitide and rose 3.0% with placebo, an adjusted difference of −55.8 percentage points (95% CI −60.9 to −50.7; p<0.001); week 52 LDL-cholesterol, non-HDL cholesterol, apolipoprotein B and lipoprotein(a) were all significantly improved, and adverse event rates did not appear to differ (Navar et al., New England Journal of Medicine, 2026;394(6):529–539). The FDA label adds that when biologically implausible LDL-cholesterol values of zero or below were set to missing in a post hoc analysis, the placebo-adjusted difference was −60% (95% CI −62 to −57).

CORALreef HeFH (NCT05952869). A parallel phase 3 trial at 59 sites in 17 countries randomized 303 adults with clinically or genetically diagnosed heterozygous familial hypercholesterolemia, all on statins and 64% on ezetimibe, 2:1 to enlicitide 20 mg or placebo for 52 weeks. Mean baseline LDL-cholesterol was 119 mg/dL. The week 24 change was −58.2% versus +2.6%, a difference of −59.4% (95% CI −65.6 to −53.2; p<0.001), and the week 52 difference was −61.5%; 96.7% of participants completed the trial, and serious adverse events and discontinuations were similar between groups (Ballantyne et al., JAMA, 2026;335(2):129–139).

CORALreef AddOn (NCT06450366). An active-comparator phase 3 trial randomized 301 statin-treated adults to enlicitide 20 mg, bempedoic acid 180 mg, ezetimibe 10 mg or the bempedoic acid–ezetimibe combination for 56 days. LDL-cholesterol fell 64.6% with enlicitide versus 6.3% with bempedoic acid, 27.8% with ezetimibe and 36.5% with the combination, with enlicitide superior to each comparator (p<0.001) and similar adverse event rates (Catapano et al., JACC, 2026;88(3):340–352).

Regulatory path. The FDA granted enlicitide a Commissioner’s National Priority Voucher on December 19, 2025. The new drug application was received on June 22, 2026, and NDA 220848 was approved on July 15, 2026 as a priority new molecular entity without referral to an advisory committee. The approved indication is as an adjunct to diet and exercise to reduce LDL-cholesterol in adults with hypercholesterolemia, including heterozygous familial hypercholesterolemia. The label lists no contraindications and has no warnings-and-precautions section. The approval letter waives pediatric studies in children under 6 and defers a placebo-controlled study in 6- to 17-year-olds with heterozygous familial hypercholesterolemia, with study completion due in January 2036 and a final report due in July 2036.

Ongoing trials. CORALreef Outcomes (NCT06008756) is the cardiovascular outcomes trial: an event-driven, placebo-controlled phase 3 study that began on October 9, 2023, has completed enrollment of about 14,550 participants with established atherosclerotic disease or at high risk of a first event, and tests whether enlicitide 20 mg daily lengthens the time to a first major adverse cardiovascular event, defined as coronary heart disease death, myocardial infarction, ischemic stroke, acute limb ischemia or major amputation, or urgent arterial revascularization. Primary completion is estimated for November 29, 2029. Until it reads out, the claim that enlicitide prevents events rests on extrapolation from statin and antibody PCSK9 outcomes trials, as the label itself states. CORALreef Extension (NCT06492291) is an open-label extension of about 3,000 participants running to October 2028; CORALreef Pediatric (NCT07058077), a phase 2/3 study in 153 children and adolescents aged 6 to 17 with heterozygous familial hypercholesterolemia, began on August 21, 2025; and a phase 3 study of enlicitide in combination with rosuvastatin (NCT07216482, 996 participants) reached primary completion on August 3, 2026 and is unpublished.

Common dosage forms

• Lipfendra tablets. 20 mg film-coated tablets with sodium caprate, supplied in 30-count and 7-count bottles.
• Investigational oral formulations. Enlicitide chloride at 6, 12, 18 and 30 mg in the phase 2b trial, and enlicitide decanoate 20 mg tablets in the phase 3 program, supplied only to clinical-trial sites.
• No other presentation. No injectable, nasal, capsule or compounded presentation exists.

Key considerations

• Regulatory status. The FDA Approved status reflects the July 15, 2026 approval of Lipfendra (enlicitide) tablets under NDA 220848 for LDL-cholesterol lowering in adults with hypercholesterolemia, including heterozygous familial hypercholesterolemia. It is the first oral PCSK9 inhibitor approved by the FDA.
• Approval rests on LDL-cholesterol, not events. All four completed trials measured lipid changes over 8 to 52 weeks. Whether enlicitide reduces heart attacks, strokes or death will not be known until CORALreef Outcomes reports; its primary completion is estimated for November 29, 2029, and the label states that the cardiovascular benefit is inferred from trials of statins and antibody PCSK9 inhibitors.
• Safety record is short. Across 2,137 enlicitide-treated participants in placebo-controlled trials, adverse events, serious adverse events and discontinuations matched placebo; the only imbalances the label reports are diarrhea (7 versus 2%) and dizziness (9 versus 4%) in the smaller HeFH trial. Exposure beyond one year is limited to the open-label extension, and the label notes that lowering LDL-cholesterol during pregnancy could in principle affect fetal development, a class-wide mechanistic caution rather than an observed signal.
• Low and food-sensitive absorption. Oral bioavailability is about 1% and depends on the sodium caprate in the tablet; the label reports that exposure falls by roughly half when the tablet is taken shortly after a meal, the main practical difference from the injected PCSK9 antibodies.
• Naming and salts. MK-0616, enlicitide, enlicitide chloride, enlicitide decanoate and Lipfendra all refer to the same cationic macrocycle; the chloride is the INN form used in the phase 2b trial and the decanoate is the USAN and JAN form and the salt in the marketed tablet. Strengths are expressed as enlicitide base. The compound is unrelated to the injected PCSK9 antibodies evolocumab and alirocumab, to the siRNA inclisiran and to the fusion protein lerodalcibep, although it shares their target; AZD0780 is a competing oral small-molecule PCSK9 inhibitor, not an alias.