PCSK9 Inhibitors
High-yield Verified · Oct 2026Every LDL receptor can clear many LDL particles if it keeps recycling. PCSK9 ends that cycle by escorting the receptor to the lysosome; the antibodies take PCSK9 out of circulation, so the receptor survives — the whole effect depends on the patient having receptors to save.
Nursing view → administration, monitoring and patient teaching
Compare: Lipid-lowering agents compared →
Drugs
Mechanism
Evolocumab and alirocumab are human monoclonal antibodies against proprotein convertase subtilisin kexin type 9 (PCSK9). PCSK9 binds LDL receptors on hepatocytes and promotes their degradation in the liver; by blocking PCSK9 binding to the LDL receptor, the antibodies increase the number of LDL receptors available to clear LDL, lowering LDL cholesterol.
The LDL receptor cycle and its feedback
LDL is cleared when apolipoprotein B100 on its surface binds LDL receptors on hepatic and extrahepatic tissues. The bound LDL is taken in by endocytosis, the vesicle fuses with lysosomes, and free cholesterol rises inside the cell. That triggers three responses: HMG-CoA reductase activity falls, ACAT activation stores more cholesterol as ester, and fewer LDL receptors are expressed on the surface.
LDL receptors normally recycle back to the cell surface to bind and clear more LDL. When LDL is very high or modified (glycated or oxidized), more is taken up by the scavenger pathway on endothelial cells, contributing to atherosclerotic plaque. Statins act upstream: by inhibiting HMG-CoA reductase they lower intracellular cholesterol, which increases LDL-receptor recycling and expression.
PCSK9: the receptor’s off-switch — and what genetics proved
PCSK9, a serine protease made by hepatocytes, is secreted into plasma, where it binds LDL receptors and facilitates their lysosomal degradation; fewer receptors reach the surface and LDL clearance falls. Statins increase PCSK9 activity, and that rise diminishes their own efficacy.
Genetics validated the target. Gain-of-function PCSK9 mutations cause autosomal dominant familial hypercholesterolemia — very high LDL-C, premature atherosclerosis and tendon xanthomas — in families with no LDL-receptor or apoB100 mutation. People with loss-of-function PCSK9 variants have modestly lower LDL-C but a larger reduction in coronary heart disease; mice that overexpress PCSK9 have high LDL, and knockout mice have high LDL-receptor activity and low LDL-C.
Antibody, siRNA — and the patient with no receptors
The antibodies bind PCSK9 in the circulation: after a subcutaneous dose, unbound circulating PCSK9 is maximally suppressed within hours (by 4 hours for evolocumab, 4–8 hours for alirocumab), and LDL-C reaches its lowest point 2–3 weeks after a single evolocumab dose; LDL-C typically falls 50–60%, with or without a statin. Inclisiran, by contrast, is a small interfering RNA that inhibits PCSK9 synthesis inside the hepatocyte, lowering LDL-C by about 50% on top of maximally tolerated statin therapy.
Because the drugs act by saving receptors, they need receptors to save. In homozygous familial hypercholesterolemia, patients with two LDL-receptor-negative alleles (little or no residual receptor function) did not respond to evolocumab and had minimal to absent response to alirocumab.
Comparing the drugs
Evolocumab versus alirocumab
| Drug | Antibody | Bioavailability (SC) | Peak | Half-life | Free PCSK9 nadir | Familial hypercholesterolemia labeling |
|---|---|---|---|---|---|---|
| Evolocumab | Human IgG2 | 72% | 3–4 days | Effective 11–17 days | By 4 hours | HeFH and HoFH from age 10 |
| Alirocumab | Human monoclonal antibody | About 85% | 3–7 days | 17–20 days (12 days with a statin) | 4–8 hours | HeFH from age 8; HoFH in adults |
Both show target-mediated, non-linear kinetics: at low concentrations they are cleared mainly by saturable binding to PCSK9, at high concentrations by non-saturable proteolysis.
Three ways to raise LDL-receptor numbers
| Drug | Mechanism | Effect on PCSK9 |
|---|---|---|
| Statins | Inhibit HMG-CoA reductase → ↓ cell cholesterol → ↑ receptor recycling and expression | Increase PCSK9 activity (blunting their effect) |
| Evolocumab, alirocumab | Bind circulating PCSK9 so it cannot bind the receptor | Free PCSK9 suppressed within hours |
| Inclisiran | Small interfering RNA | Inhibits intracellular PCSK9 synthesis |
Pharmacokinetics
- Absorption
- Subcutaneous bioavailability is 72% for evolocumab and about 85% for alirocumab; peak serum levels come 3–4 days (evolocumab) or 3–7 days (alirocumab) after a dose, and alirocumab exposure is similar whether injected into the abdomen, upper arm or thigh.
- Distribution
- Mostly confined to the circulation — steady-state volume about 3.3 L for evolocumab and 0.04–0.05 L/kg for alirocumab after intravenous dosing.
- Target-mediated elimination
- Two elimination phases: at low concentrations, saturable binding to PCSK9; at higher concentrations, non-saturable proteolysis. Evolocumab therefore shows non-linear kinetics. Alirocumab, a protein, is expected to be degraded to small peptides and amino acids.
- Half-life
- Effective half-life 11–17 days for evolocumab; 17–20 days for alirocumab at steady state, shortened to 12 days with a statin (not clinically meaningful).
- Renal and hepatic impairment
- Monoclonal antibodies are not known to be eliminated renally; no dose adjustment is needed in renal impairment. Evolocumab exposure was lower in mild to moderate hepatic impairment; alirocumab exposure was similar.
- Immunogenicity
- Binding antibodies developed in 0.3% of adults on evolocumab, none neutralizing; anti-drug antibodies developed in 5.5% on alirocumab (0.5% neutralizing), and some with persistent or neutralizing antibodies had a weaker LDL-C response.
Pharmacogenomics
Uses & drug choice
- Prevention of major cardiovascular events (such as myocardial infarction, stroke and unstable angina requiring hospitalization) in adults at increased risk
- Hypercholesterolemia — with diet and exercise to lower LDL-C, including heterozygous familial hypercholesterolemia (evolocumab from age 10, alirocumab from age 8) and homozygous familial hypercholesterolemia (evolocumab in adults and children 10 and older; alirocumab in adults)
Adverse effects
- Injection-site reactions
- Local reactions to subcutaneous injection (redness, pain, bruising, itching, swelling); they were more frequent with alirocumab every 4 weeks than every 2 weeks (16.6% versus 9.6%) and in patients with anti-drug antibodies (7.5% versus 3.6%).
- Hypersensitivity, angioedema, vasculitis
- Serious hypersensitivity reactions to the drug or its excipients — angioedema with both, hypersensitivity vasculitis with alirocumab — are why a history of them is the only contraindication.
- Latex reaction (some evolocumab presentations)
- Dry natural rubber, a latex derivative, in the needle cover of some autoinjectors and syringes.
- Weaker LDL-C response with alirocumab antibodies
- Persistent or neutralizing anti-alirocumab antibodies attenuated LDL-C lowering in some adults.
Interactions
Contraindications
- History of serious hypersensitivity reaction to evolocumab or alirocumab, or to any excipient — Serious hypersensitivity reactions, including angioedema, have occurred with both drugs.
- Latex sensitivity (evolocumab presentations with a dry natural rubber needle cover) use caution — The needle cover may cause an allergic reaction; a latex-free presentation can be used instead.
High-yield
- Pulls — PCSK9 binds the LDL receptor
- Keys for good — and sends it to the lysosome, so it never recycles
- Block PCSK9 (evolocumab, alirocumab) → receptors keep recycling → LDL-C ↓ 50–60%
- No keys at all (two receptor-negative alleles) → nothing to save → no response
Practice questions
Q1A 54-year-old man with coronary disease has an LDL-C of 98 mg/dL despite high-intensity atorvastatin. His physician explains that the statin itself limits how far LDL-C can fall and adds a subcutaneous antibody every 2 weeks; 6 weeks later LDL-C is 41 mg/dL.
Which effect of statins does the added drug counteract?
- A.Increased hepatic cholesterol synthesis
- B.Decreased LDL-receptor expression
- C.Increased intestinal cholesterol absorption
- D.Increased PCSK9 activity
- E.Decreased lipoprotein lipase activity
Show answer
D. Increased PCSK9 activity — Statins lower intracellular cholesterol and increase LDL-receptor expression, but they also increase PCSK9 activity, which diminishes their efficacy. A PCSK9 antibody such as evolocumab or alirocumab blocks PCSK9 binding to the LDL receptor, so more receptors recycle and clear LDL; LDL-C typically falls 50–60% with or without a statin.
Q2A 19-year-old with homozygous familial hypercholesterolemia has an LDL-C above 500 mg/dL. Genetic testing shows two LDL-receptor-negative alleles. Evolocumab is added for 12 weeks without any fall in LDL-C.
What best explains the lack of response?
- A.Neutralizing anti-drug antibodies
- B.Rapid renal clearance of the antibody
- C.No functional LDL receptors for the drug to preserve
- D.Concurrent statin therapy raising PCSK9
- E.A gain-of-function PCSK9 mutation
Show answer
C. No functional LDL receptors for the drug to preserve — PCSK9 antibodies lower LDL-C by increasing the number of LDL receptors available to clear LDL. Patients with two LDL-receptor-negative alleles (little or no residual function) did not respond to evolocumab in the HoFH trial. Monoclonal antibodies are not known to be renally eliminated, and only 0.3% of evolocumab patients developed binding antibodies, none neutralizing.
Q3A research team studies a family with autosomal dominant hypercholesterolemia, tendon xanthomas and premature coronary disease, but no mutation in the LDL receptor or apolipoprotein B100.
A mutation in which gene, with which effect, is most likely?
- A.HMG-CoA reductase, loss of function
- B.PCSK9, gain of function
- C.Lipoprotein lipase, loss of function
- D.PCSK9, loss of function
- E.ACAT, gain of function
Show answer
B. PCSK9, gain of function — Gain-of-function PCSK9 mutations cause autosomal dominant familial hypercholesterolemia — high LDL-C, premature atherosclerosis and tendon xanthomas — and were first found in a family without LDL-receptor or apoB100 mutations. PCSK9 loss of function does the opposite: lower LDL-C and less coronary heart disease.
Q4A patient asks why her new cholesterol drug is an injection every 2 weeks that must be kept in the refrigerator, while a newer drug her friend takes is given only twice a year after the first two doses.
Which statement best contrasts the two drugs?
- A.Both are monoclonal antibodies with different half-lives
- B.Her drug inhibits HMG-CoA reductase; her friend’s drug is a PCSK9 antibody
- C.Both block cholesterol absorption in the gut
- D.Her drug degrades LDL receptors; her friend’s drug synthesizes new receptors
- E.Her drug is a PCSK9 antibody that binds circulating PCSK9; her friend’s is an siRNA that blocks PCSK9 synthesis inside liver cells
Show answer
E. Her drug is a PCSK9 antibody that binds circulating PCSK9; her friend’s is an siRNA that blocks PCSK9 synthesis inside liver cells — Evolocumab and alirocumab are monoclonal antibodies that bind PCSK9 and stop it binding the LDL receptor, given subcutaneously every 2 to 4 weeks. Inclisiran is a small interfering RNA that inhibits intracellular PCSK9 synthesis, given initially, at 3 months and then every 6 months.
Sources
- REPATHA (evolocumab) — FDA label: indications, administration, storage, hypersensitivity, latex — FDA / DailyMed
- PRALUENT (alirocumab) — FDA label: indications, administration, storage, hypersensitivity — FDA / DailyMed
- PCSK9 Inhibitors — LDL-receptor recycling, PCSK9 and statins, LDL-C reduction — StatPearls (NCBI)
- The use of stems in the selection of INN (2018) — -mab, -ci- (cardiovascular), -u- (human) — World Health Organization
- Table of Pharmacogenomic Biomarkers in Drug Labeling — U.S. FDA
By LearnDrugs
Educational summary for medical students. Always verify against current prescribing information and guidelines. Not medical advice.