Simvastatin

HMG-CoA reductase inhibitors (statins)

ATC code: C10AA01 (Simvastatin)

Mechanism of action

Prodrug (lactone). Activated in the liver by hydrolysis to the beta-hydroxy acid form, which competitively inhibits HMG-CoA reductase. Short half-life of approximately 2 hours, so it must be taken in the evening when hepatic cholesterol synthesis peaks. Metabolized via CYP3A4, creating numerous drug interactions.

Indications

Dyslipidemia, primary CV prevention

First line

Prescribed for primary prevention in patients with elevated cardiovascular risk. Dose 20-40 mg in the evening. The 80 mg dose is no longer recommended – FDA restricted it in 2011 due to increased myopathy and rhabdomyolysis risk. New patients do not start at 80 mg; it is retained only for those who have taken it for over 12 months without adverse effects.

Established ASCVD, secondary prevention

First line

Simvastatin demonstrated efficacy in landmark RCTs – 4S (30% reduction in all-cause mortality) and HPS (24% reduction in vascular events). These trials laid the evidence foundation for the entire statin class. In current practice, atorvastatin and rosuvastatin are preferred due to more potent LDL reduction and fewer interactions. Simvastatin remains a reasonable choice at doses up to 40 mg.

Practical notes

Timing and administration

Take in the evening – mandatory. Half-life is only 2 hours, and cholesterol synthesis peaks at night. Morning dosing reduces efficacy by 30-50%. Atorvastatin and rosuvastatin can be taken at any time due to their long half-lives, but simvastatin must be taken in the evening.

Special situations

Maximum dose is 40 mg. The 80 mg dose is not started in new patients (FDA 2011). Simvastatin is metabolized via CYP3A4, creating many interactions. Contraindicated with itraconazole, ketoconazole, erythromycin, clarithromycin, HIV protease inhibitors, nefazodone. With amiodarone, verapamil, or diltiazem, the maximum dose is 20 mg. Grapefruit juice increases simvastatin levels – avoid large quantities.

Safety

Contraindications

Active liver disease or unexplained persistent transaminase elevation
Pregnancy and planned pregnancy (FDA category X)
Breastfeeding
Concurrent potent CYP3A4 inhibitors – itraconazole, ketoconazole, erythromycin, clarithromycin, HIV protease inhibitors
Concurrent gemfibrozil, cyclosporine, or danazol

Serious adverse effects

Myopathy and rhabdomyolysis – risk higher than other statins at 80 mg and with drug interactions
Immune-mediated necrotizing myopathy (very rare)
Hepatotoxicity (rare)

Common adverse effects

Myalgia
Headache
Dyspepsia, nausea, constipation
Transaminase elevation (usually transient)

PregnancyFDA X

FDA category X. Cholesterol is essential for fetal development. Statins are contraindicated in pregnancy. Discontinue at least 3 months before planned conception.

Breastfeeding

Contraindicated during breastfeeding.