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PH4.11 | PH4.11 | Dyslipidaemia Pharmacotherapy — SDL Guide (Part 2)

Statins: PK, PD, Uses, and Adverse Effects

Statins are the cornerstone of dyslipidaemia pharmacotherapy. They are structural analogues of HMG-CoA and competitively inhibit HMG-CoA reductase, the enzyme catalysing the rate-limiting step of cholesterol biosynthesis (HMG-CoA → mevalonate). The resulting reduction in intracellular cholesterol triggers upregulation of LDL receptors on hepatocytes, increasing LDL clearance from the plasma and reducing circulating LDL-C by 20–60% depending on the drug and dose.

Pharmacokinetics: Statins are administered orally. Most undergo extensive first-pass hepatic metabolism (high hepatic extraction ensures target-organ selectivity and limits systemic exposure). Lovastatin and simvastatin are prodrugs (lactone form converted to active hydroxy-acid in the liver); the others (atorvastatin, rosuvastatin, pravastatin, fluvastatin) are administered as active hydroxy-acids. Atorvastatin and rosuvastatin have longer half-lives (~14 h and ~19 h respectively) and can be taken at any time of day; others with shorter half-lives (pravastatin, lovastatin, simvastatin) are traditionally taken at night to match the nocturnal peak of cholesterol synthesis. Rosuvastatin and pravastatin have negligible CYP450 metabolism, making them safer in patients on multiple CYP3A4 substrates.

Intensity classification:
- High-intensity (≥50% LDL reduction): atorvastatin 40–80 mg/day; rosuvastatin 20–40 mg/day
- Moderate-intensity (30–49% reduction): atorvastatin 10–20 mg, rosuvastatin 5–10 mg, simvastatin 20–40 mg, pravastatin 40–80 mg, lovastatin 40 mg
- Low-intensity (<30%): simvastatin 10 mg, pravastatin 10–20 mg (rarely used as first-line)

Pleiotropic effects (beyond LDL lowering): improved endothelial function, anti-inflammatory actions (reduced hsCRP), plaque-stabilisation (thickening the fibrous cap), antithrombotic effect. These contribute to the early cardiovascular benefit seen even before LDL changes.

Adverse drug reactions:
1. Myopathy spectrum — the most important class ADR. Mild myalgia (muscle pain without CK elevation, 5–10% of patients; usually dose-related) → myositis (CK elevation <10× ULN with symptoms) → rhabdomyolysis (CK >10× ULN + myoglobinuria + acute kidney injury; rare but life-threatening). Risk factors: high dose, renal/hepatic impairment, hypothyroidism, concurrent fibrate (especially gemfibrozil — increase myopathy risk significantly; fenofibrate is safer), concurrent CYP3A4 inhibitors (clarithromycin, itraconazole, HIV PIs, ciclosporin), grapefruit juice (simvastatin/lovastatin).
2. Hepatotoxicity — transaminase elevation >3× ULN in ~1% of patients; monitor LFTs. Avoid in active liver disease.
3. New-onset diabetes mellitus — modest but real; high-intensity statins carry greater risk. The cardiovascular benefit outweighs this risk.
4. Cognitive effects — FDA warning (statin-associated memory impairment); generally reversible on stopping; no definitive causal evidence.
5. Teratogenicity — contraindicated in pregnancy (inhibition of cholesterol synthesis harms fetal development).

Drug interactions: Major DDIs arise from CYP3A4 inhibition increasing levels of simvastatin/lovastatin/atorvastatin → myopathy risk. Bile-acid sequestrants reduce statin absorption if taken simultaneously (give statins 1 hour before or 4 hours after BAS).

Non-Statin Agents: Fibrates, Ezetimibe, PCSK9 Inhibitors, and Others

Several non-statin agents extend the therapeutic armamentarium for dyslipidaemia, each acting at a distinct site in lipid metabolism.

Fibrates (PPAR-α agonists): Prototype drugs include gemfibrozil and fenofibrate. They activate peroxisome proliferator-activated receptor-alpha (PPAR-α) in hepatocytes, which increases lipoprotein lipase (LPL) activity (promoting VLDL triglyceride hydrolysis), reduces hepatic VLDL synthesis, and modestly raises HDL-C. The net result is a 30–50% reduction in triglycerides — making fibrates first-line for severe hypertriglyceridaemia. Gemfibrozil inhibits CYP2C8 and the glucuronidation pathway for statin acid forms, causing a pharmacokinetic interaction that markedly increases statin levels and myopathy risk — gemfibrozil should not be combined with statins unless the benefit clearly outweighs the risk. Fenofibrate is the preferred fibrate when a statin combination is necessary. ADRs: GI upset (most common), cholelithiasis (increased biliary cholesterol secretion), myopathy when combined with statins, mild transaminase elevation.

Ezetimibe: Acts at the intestinal brush border by inhibiting the NPC1L1 (Niemann-Pick C1-Like 1) cholesterol transporter, reducing dietary and biliary cholesterol absorption. Reduces LDL-C by 15–20% as monotherapy or when added to statins. The IMPROVE-IT trial confirmed that ezetimibe added to simvastatin in post-ACS patients further reduced LDL-C and modestly reduced cardiovascular events, validating the LDL hypothesis for non-statin therapy. Well-tolerated; minimal drug interactions.

PCSK9 inhibitors: Evolocumab (Repatha) and alirocumab (Praluent) are fully human or humanised monoclonal IgG1 antibodies that bind PCSK9, preventing it from degrading LDL receptors. The result is a striking 50–60% reduction in LDL-C on top of maximally tolerated statin. The FOURIER trial (evolocumab) and ODYSSEY OUTCOMES trial (alirocumab) demonstrated significant reduction in MACE in patients with established ASCVD on statin therapy. Administered by subcutaneous injection fortnightly or monthly. Cost limits use to high-risk patients (FH, statin intolerance, established ASCVD not at target).

Bile-acid sequestrants (BAS): Cholestyramine, colestipol, and colesevelam are large-molecule anion-exchange resins that bind bile acids in the intestinal lumen, preventing their enterohepatic recirculation. The liver compensates by converting more cholesterol to bile acids, depleting hepatic cholesterol and upregulating LDL receptors — reducing LDL-C by 15–30%. They are not absorbed, making them safe in pregnancy. Key limitations: poor tolerability (bloating, constipation), raise triglycerides (contraindicated in hypertriglyceridaemia TG >300 mg/dL), and bind many drugs reducing their absorption (give other drugs 1 hour before or 4 hours after BAS).

Niacin (nicotinic acid): Reduces free fatty acid release from adipose tissue via GPR109A receptor, decreasing hepatic VLDL synthesis. Most powerful HDL-C raising agent (+15–35%) and also reduces TG by 20–50% and LDL-C by 15–20%. Largely superseded: AIM-HIGH and HPS2-THRIVE trials showed no clinical benefit of niacin added to statin, despite HDL elevation. Flushing (mediated by prostaglandin D2; mitigated by aspirin pre-treatment) is the primary tolerability issue; also causes hepatotoxicity and worsens glucose control.

Omega-3 fatty acids: High-dose eicosapentaenoic acid (EPA, 4 g/day as icosapentaenoic acid ethyl ester — Vascepa) demonstrated a 25% relative reduction in MACE in statin-treated patients with TG 135–499 mg/dL and established CVD or diabetes in the REDUCE-IT trial. DHA-containing preparations had neutral cardiovascular results in STRENGTH trial. Mechanism of triglyceride lowering: reduced hepatic VLDL-TG assembly. Well-tolerated; mild fishy taste, atrial fibrillation risk at high doses.

Clinical Decision-Making in Dyslipidaemia

Effective management of dyslipidaemia requires integrating the drug's pharmacology with the patient's cardiovascular risk profile, comorbidities, and concomitant therapy. The following frameworks guide prescribing decisions in common clinical contexts.

Choosing intensity: In patients with established ASCVD (secondary prevention), high-intensity statin (atorvastatin 40–80 mg or rosuvastatin 20–40 mg) should be initiated regardless of baseline LDL. For primary prevention, intensity is tailored to risk tier. When additional LDL lowering is needed beyond the maximally tolerated statin, add ezetimibe first (cheaper, oral, well-tolerated); if LDL target still not met in very-high-risk or FH patients, add a PCSK9 inhibitor.

Special populations:

• Chronic kidney disease (CKD): Statin dose adjustment is needed for renally excreted statins (rosuvastatin — reduce dose in eGFR <30; pravastatin). Atorvastatin and fluvastatin are primarily hepatically eliminated and are safer in advanced CKD. Fibrates require dose reduction in CKD; avoid gemfibrozil (myopathy risk). BAS are safe (not absorbed) but may raise TG.

• Diabetes mellitus: Statins increase the risk of new-onset T2DM by ~10% at moderate intensity and ~20% at high intensity. In patients with established CVD + diabetes, the cardiovascular benefit far outweighs this risk — continue high-intensity statin. In primary prevention in diabetes, risk–benefit must be calculated; most guidelines recommend statin for T2DM patients with any additional risk factor or age >40 years.

• Pregnancy: Statins are contraindicated (category X / teratogenic — fetal cholesterol is essential for myelin and hormone synthesis). Bile-acid sequestrants are the only class considered safe (not absorbed). FH management in pregnancy: maximise diet, consider BAS if LDL dangerously elevated; PCSK9 inhibitors — insufficient safety data, generally avoided.

• Liver disease: Active hepatitis or unexplained transaminase elevation >3× ULN — contraindication for statins. Compensated cirrhosis or MASLD (metabolic-associated steatotic liver disease) — statins can be safely used and may even benefit liver inflammation.

• Elderly (>75 years): Benefit in secondary prevention persists; in primary prevention the risk–benefit balance is less clear. Statin-associated myopathy is more common due to lower muscle mass and polypharmacy.

Monitoring:
- LFTs: baseline, then at 8–12 weeks after initiation and dose increase; periodic thereafter
- CK: at baseline; recheck only if myalgia develops — do not monitor CK routinely
- Fasting lipid profile: 4–12 weeks after initiation; repeat at 3 months to assess response; annually if stable
- HbA1c: monitor in patients with risk of diabetes

Self-Assessment and Key Takeaways

This section consolidates your learning from this SDL. Review the following self-assessment prompts before attempting the MCQ assessment.

Mechanism-action review:
- Statins → HMG-CoA reductase inhibition → ↑hepatic LDL-R → ↓LDL-C
- Fibrates → PPAR-α activation → ↑LPL activity + ↓VLDL synthesis → ↓TG
- Ezetimibe → NPC1L1 inhibition → ↓intestinal cholesterol absorption → ↓LDL-C
- BAS → bile-acid sequestration → ↑hepatic bile-acid synthesis from cholesterol → ↑LDL-R → ↓LDL-C
- PCSK9 inhibitors → anti-PCSK9 antibody → ↑LDL-R survival → ↓LDL-C 50–60%
- Niacin → GPR109A → ↓adipose FFA release → ↓VLDL synthesis → ↑HDL, ↓TG

Drugs causing dyslipidaemia (must-know list):
1. Thiazide diuretics — ↑LDL, ↑TG (high dose)
2. Non-selective β-blockers — ↑TG, ↓HDL
3. Corticosteroids — ↑LDL, ↑TG
4. Oral contraceptives / oestrogens — ↑TG (especially oral), ↑LDL
5. Retinoids (isotretinoin) — ↑TG, ↑LDL, ↓HDL
6. Protease inhibitors (HIV antiretrovirals) — ↑TG, ↑LDL
7. Ciclosporin — ↑LDL

Key numbers to remember:
- High-intensity statin: atorvastatin 40–80 mg; rosuvastatin 20–40 mg
- LDL target, secondary prevention / very-high risk: <70 mg/dL
- TG >500 mg/dL: fibrate first (pancreatitis risk)
- PCSK9 inhibitors: ↓LDL by 50–60% on top of statin (FOURIER/ODYSSEY evidence)

Contraindications quick summary:
- Statins: pregnancy, active liver disease, concurrent gemfibrozil (relative)
- BAS: hypertriglyceridaemia (TG >300 mg/dL)
- Fibrates (gemfibrozil): concurrent statin (myopathy risk)
- PCSK9 inhibitors: cost / access barrier, not absolute contraindication