Simvastatin: HMG-CoA Reductase Inhibitor (Statin)
Simvastatin is a semi-synthetic, inactive lactone prodrug converted to its active form in the liver. It is an HMG-CoA reductase inhibitor that reduces hepatic cholesterol synthesis, increases LDL receptor expression, and lowers LDL-C by 25–40% depending on dose.
One of the most studied statins, simvastatin demonstrated significant cardiovascular mortality reduction in the 4S trial. The 80 mg dose was restricted due to high myopathy risk and is no longer recommended for new patients.
Mechanism of Action
Simvastatin inhibits HMG-CoA reductase, the rate-limiting enzyme in hepatic cholesterol biosynthesis. This reduces intracellular cholesterol, upregulates LDL receptors on hepatocytes, increases LDL clearance from plasma, and has pleiotropic anti-inflammatory and endothelial stabilising effects.
Indications & Use
Primary and secondary prevention of cardiovascular events in hypercholesterolaemia and mixed dyslipidaemia. Familial hypercholesterolaemia (heterozygous). Reduction of LDL-C in high-risk patients with type 2 diabetes or established cardiovascular disease.
Dosage
5–40 mg once daily in the evening (evening dosing preferred as cholesterol synthesis peaks at night). Maximum 40 mg/day. The 80 mg dose is not recommended for new initiations. Dose reduction required with certain interacting drugs.
Side Effects
Common: myalgia (muscle aches, 5–10% of patients). Rare but serious: myopathy, rhabdomyolysis (higher risk at 80 mg or with interacting drugs). Elevated liver enzymes (rare at low-moderate doses). New-onset diabetes (class effect).
Drug Interactions
Strong CYP3A4 inhibitors (itraconazole, clarithromycin, HIV protease inhibitors): contraindicated — risk of rhabdomyolysis. Amiodarone, amlodipine: max 20 mg simvastatin. Gemfibrozil: contraindicated. Bempedoic acid: max 20 mg simvastatin.
Contraindications
Active liver disease, unexplained persistent elevation of liver enzymes, pregnancy and breastfeeding, concomitant use of strong CYP3A4 inhibitors, myopathy.
Frequently Asked Questions
Why should simvastatin be taken in the evening?
Hepatic cholesterol synthesis follows a circadian rhythm and peaks at night. Taking simvastatin in the evening aligns its maximum inhibitory effect with peak synthesis, improving efficacy.
Do I need to stop statins if my muscles hurt?
Mild muscle aches (myalgia) without CK elevation are common and do not require stopping. If muscle pain is severe, persistent, or accompanied by weakness and dark urine, seek medical advice immediately — this may indicate myopathy or rhabdomyolysis.
Are all statins the same?
No — statins vary in potency, hydrophilicity, and drug interactions. Simvastatin is moderately potent and highly susceptible to CYP3A4 interactions. Rosuvastatin and atorvastatin are more potent; rosuvastatin has fewer drug interactions.
References
- 4S Trial (simvastatin in coronary heart disease)
- ESC Dyslipidaemia Guidelines 2019
- FDA simvastatin drug interaction update
Medical Disclaimer: This information is for educational purposes only and does not replace professional medical advice.