Which of the following is a PCSK9 inhibitor?

Correct Answer: C. Evolocumab

Evolocumab is a monoclonal antibody PCSK9 inhibitor that represents a paradigm shift in lipid-lowering therapy. PCSK9 (proprotein convertase subtilisin/kexin type 9) is a protein that binds to LDL receptors on hepatocytes and promotes their degradation, thereby reducing LDL uptake from circulation. By inhibiting PCSK9, evolocumab prevents this degradation, increasing the number of functional LDL receptors on the liver surface and enhancing LDL-cholesterol clearance from blood. This mechanism is distinct from statins (which inhibit HMG-CoA reductase) and ezetimibe (which blocks cholesterol absorption). Evolocumab can reduce LDL-C by 50–70% when added to statin therapy, making it particularly valuable in patients with familial hypercholesterolaemia (FH), statin-intolerant patients, and those at very high cardiovascular risk. In India, evolocumab is increasingly used in tertiary care settings for high-risk patients, though cost remains a limiting factor. The drug is administered as a subcutaneous injection every 2 weeks or monthly, depending on the formulation. PCSK9 inhibitors are now recognized as second-line agents after statins in the management of dyslipidaemia according to international guidelines.

Why the other options are wrong

A. Ezetimibe — Ezetimibe is a cholesterol absorption inhibitor that blocks the Niemann-Pick C1-like 1 (NPC1L1) transporter in the small intestine, reducing dietary cholesterol uptake. It works at the intestinal level, not by targeting PCSK9. While ezetimibe is commonly used as add-on therapy to statins in India (especially in patients with inadequate LDL-C lowering), it is fundamentally a different drug class and does not inhibit PCSK9. B. Bempedoic acid — Bempedoic acid is a uricosuric agent and LDLC-lowering drug that inhibits AMPK-activated protein kinase and reduces uric acid reabsorption while lowering LDL-C through inhibition of AMP deaminase. It is a newer non-statin agent approved for dyslipidaemia, but it does not inhibit PCSK9. Bempedoic acid is particularly useful in gout patients with dyslipidaemia, but it operates via a completely different mechanism. D. Clofibrate — Clofibrate is a fibrate (peroxisome proliferator-activated receptor agonist) that primarily lowers triglycerides and raises HDL-C by activating PPAR-α. Although largely replaced by newer fibrates like fenofibrate in modern practice, clofibrate has no role in PCSK9 inhibition. Fibrates work through lipase activation and VLDL reduction, not LDL receptor upregulation via PCSK9 inhibition.

High-Yield Facts

Mnemonics

PCSK9 = 'P-Cuts Statins' Killer 9 PCSK9 destroys LDL receptors → inhibiting PCSK9 preserves receptors → more LDL uptake. Evolocumab blocks PCSK9 with a monoclonal antibody. Use this when you need to remember that PCSK9 inhibitors work downstream of statin action. Non-Statin Lipid Agents: 'EBFC' Ezetimibe (absorption blocker), Bempedoic acid (uricosuric), Fibrates (TG↓), CPCSK9 inhibitors (receptor ↑). Helps distinguish mechanism when multiple non-statin options appear in a question.

NBE Trap

NBE may pair PCSK9 inhibitors with statins to test whether students confuse the mechanism (some may incorrectly think PCSK9 inhibitors also block HMG-CoA reductase like statins do). The presence of ezetimibe as an option exploits the common misconception that all non-statin lipid agents work at the intestinal level.

Clinical Pearl

In Indian tertiary care, evolocumab is increasingly prescribed for young patients with familial hypercholesterolaemia presenting with premature coronary artery disease (CAD <40 years). A single LDL-C measurement >300 mg/dL in a patient with family history of early MI should prompt PCSK9 inhibitor consideration after maximal statin + ezetimibe therapy.

_Reference: KD Tripathi Pharmacology Ch. 31 (Lipid-Lowering Agents); Harrison Principles of Internal Medicine Ch. 395 (Lipoprotein Disorders)_