A 48-year-old woman with newly diagnosed primary hypercholesterolaemia (total cholesterol 320 mg/dL, LDL-C 210 mg/dL, HDL-C 42 mg/dL, triglycerides 180 mg/dL) is started on simvastatin 20 mg daily. After 6 weeks, repeat lipids show LDL-C 165 mg/dL (21% reduction). She reports mild muscle aches but no creatine kinase elevation. What is the most appropriate next step?

Explanation

## Clinical Context This patient has: - Primary hypercholesterolaemia with suboptimal LDL response to simvastatin 20 mg (21% reduction; target is typically 30–50%) - Mild myalgia without myositis (normal CK, no rhabdomyolysis) - LDL-C still 165 mg/dL, well above goal for cardiovascular risk reduction ## Management of Statin-Induced Myalgia **Key Point:** Mild muscle symptoms with normal CK during statin therapy are common (5–10% of patients) and do NOT mandate statin discontinuation. True statin-induced myositis (CK >10× upper limit of normal with symptoms) is rare (<0.1%) and requires statin cessation. ## Statin Dose Escalation & Combination Therapy ```mermaid flowchart TD A[Suboptimal LDL response on statin monotherapy]:::outcome --> B{Tolerable side effects?}:::decision B -->|Yes| C[Increase statin dose or switch to more potent statin]:::action C --> D[Add ezetimibe 10 mg daily]:::action D --> E[Recheck lipids in 6 weeks]:::action E --> F{LDL goal achieved?}:::decision F -->|Yes| G[Continue combination therapy]:::action F -->|No| H[Add PCSK9 inhibitor]:::action B -->|No: Severe myalgia/myositis| I[Switch to pravastatin or rosuvastatin]:::action ``` ## Why Increase Simvastatin + Add Ezetimibe? **High-Yield:** 1. **Dose escalation** (simvastatin 20 → 40 mg) provides additional ~6% LDL reduction via further HMG-CoA reductase inhibition 2. **Ezetimibe addition** blocks intestinal cholesterol absorption at the Niemann-Pick C1-like 1 (NPC1L1) transporter, reducing LDL by an additional 15–20% 3. **Synergistic effect:** Combined therapy achieves ~35–40% LDL reduction, moving the patient closer to goal 4. **Myalgia is tolerable** (no CK elevation) and does not contraindicate dose escalation ## Mechanism of Ezetimibe **Key Point:** Ezetimibe inhibits cholesterol absorption in the small intestine by blocking NPC1L1 on enterocytes. This: - Reduces intestinal cholesterol delivery to the liver - Triggers compensatory upregulation of hepatic LDL receptors (synergistic with statin effect) - Lowers LDL-C by 15–20% when added to statin monotherapy - Does NOT cause myalgia or interact significantly with statins ## Why NOT the Other Options? **Niacin (Option A):** While niacin reduces LDL and raises HDL, it is less effective than ezetimibe for LDL lowering and has more side effects (flushing, hyperglycaemia, hyperuricaemia). Not preferred as add-on therapy in modern guidelines. **Pravastatin switch (Option C):** Pravastatin is lipophilic and muscle-metabolized differently than simvastatin, but myalgia here is mild with normal CK—not an indication for switch. Switching delays LDL goal achievement. **PCSK9 inhibitor monotherapy (Option D):** PCSK9 inhibitors are expensive and reserved for patients who fail dual therapy (statin + ezetimibe) or have statin intolerance. They should not be used as monotherapy or first-line. ## Statin Potency Hierarchy | Statin | Typical LDL Reduction (%) | Potency | |--------|---------------------------|----------| | Pravastatin 40 mg | 25–30 | Low | | Simvastatin 40 mg | 30–35 | Low–Moderate | | Atorvastatin 40 mg | 40–45 | Moderate–High | | Rosuvastatin 20 mg | 45–50 | High | **Mnemonic for statin intensity:** **"A Rose is Pretty"** — Atorvastatin, Rosuvastatin (high-intensity); Pravastatin (moderate). [cite:KD Tripathi 8e Ch 31; ACC/AHA Cholesterol Guidelines 2018]