Lipid-Lowering Pharmacology
Comprehensive pharmacology of statins, ezetimibe, PCSK9 inhibitors, fibrates, and other agents that reduce cardiovascular risk through lipid modification.
## Overview
Dyslipidemia, particularly elevated LDL cholesterol, is a causal risk factor for atherosclerotic cardiovascular disease (ASCVD). Pharmacological LDL lowering reduces cardiovascular events proportionally to the absolute LDL reduction achieved. Statins are the cornerstone, with additional agents for patients not reaching targets.
## Statins
Atorvastatin, rosuvastatin, simvastatin, and pravastatin competitively inhibit HMG-CoA reductase, the rate-limiting enzyme in hepatic cholesterol synthesis. Reduced intracellular cholesterol upregulates LDL receptor expression, increasing LDL clearance from plasma. High-intensity statins (atorvastatin 40-80 mg, rosuvastatin 20-40 mg) lower LDL by 50% or more. Statins also have pleiotropic effects: endothelial function improvement, plaque stabilization, and anti-inflammatory action. Myalgia occurs in 5-10% of patients, while rhabdomyolysis is rare (<0.01%).
## Ezetimibe
Ezetimibe blocks the Niemann-Pick C1-Like 1 (NPC1L1) transporter in the intestinal brush border, reducing cholesterol absorption by approximately 50%. It lowers LDL by 15-20% as monotherapy and is additive with statins. The IMPROVE-IT trial showed incremental cardiovascular benefit when added to simvastatin post-ACS.
## PCSK9 Inhibitors
Evolocumab and alirocumab are monoclonal antibodies against proprotein convertase subtilisin/kexin type 9 (PCSK9). PCSK9 normally tags LDL receptors for degradation. Blocking PCSK9 increases LDL receptor recycling, lowering LDL by 50-60% on top of statins. The FOURIER and ODYSSEY OUTCOMES trials demonstrated cardiovascular event reduction. Administered by subcutaneous injection every 2-4 weeks. Inclisiran, a small interfering RNA (siRNA) targeting PCSK9 mRNA, offers twice-yearly dosing.
## Other Agents
- **Bempedoic acid**: Inhibits ATP citrate lyase upstream of HMG-CoA reductase. Prodrug activated only in the liver (not muscle), avoiding myalgia. Lowers LDL by 15-25%. The CLEAR Outcomes trial showed cardiovascular benefit in statin-intolerant patients.
- **Fibrates** (fenofibrate, gemfibrozil): PPAR-alpha agonists that primarily lower triglycerides (30-50%) and raise HDL. Cardiovascular outcome data are inconsistent. Pemafibrate showed no benefit in PROMINENT trial.
- **Omega-3 fatty acids**: Icosapent ethyl (pure EPA) reduced cardiovascular events in REDUCE-IT (high-dose 4 g/day) in patients with elevated triglycerides on statins.
## Treatment Strategy
High-intensity statin therapy is first-line for secondary prevention and high-risk primary prevention. Ezetimibe is added if LDL remains above target. PCSK9 inhibitors are reserved for very high-risk patients or familial hypercholesterolemia not controlled by statins plus ezetimibe.
## Key Takeaways
- Statins lower LDL 30-50% by inhibiting HMG-CoA reductase and upregulating LDL receptors
- Ezetimibe and PCSK9 inhibitors provide incremental LDL reduction with proven outcomes
- Bempedoic acid avoids muscle side effects by liver-only activation
- LDL lowering benefit is proportional to absolute LDL reduction regardless of agent