Simvastatin

Brand Names: Zocor

Drug Class: HMG-CoA reductase inhibitor (statin)

Overview

Simvastatin is an HMG-CoA reductase inhibitor (statin) used to lower LDL cholesterol and reduce cardiovascular risk. It is indicated for primary hyperlipidemia, familial hypercholesterolemia, and secondary prevention in patients with established cardiovascular disease or diabetes. The drug works by inhibiting cholesterol synthesis in the liver, increasing LDL receptor expression and clearance of LDL from the bloodstream.

Mechanism of Action

Simvastatin is a prodrug that is hydrolyzed to its active beta-hydroxyacid form, which competitively inhibits HMG-CoA reductase, the rate-limiting enzyme in cholesterol biosynthesis. This inhibition decreases hepatic cholesterol synthesis, leading to upregulation of LDL receptors on hepatocytes and increased clearance of LDL cholesterol from plasma.

Indications

  • Reduce risk of coronary heart disease death, myocardial infarction, stroke, and revascularization in adults with established cardiovascular disease or diabetes
  • Adjunct to diet to reduce LDL-C in adults with primary hyperlipidemia
  • Adjunct to diet in adults and pediatric patients (≥10 years) with heterozygous familial hypercholesterolemia
  • Adjunct to other LDL-lowering therapies in adults with homozygous familial hypercholesterolemia
  • Treatment of primary dysbetalipoproteinemia
  • Treatment of hypertriglyceridemia

Common Doses

  • 5 mg
  • 10 mg
  • 20 mg
  • 40 mg
  • 80 mg

Dosage

Typical starting dose is 20-40 mg once daily in the evening, with maximum recommended dose of 40 mg daily for most patients. Some patients may require 80 mg daily, but this dose is associated with increased risk of myopathy. Dosage should be individualized based on LDL-C goals and patient response.

Contraindications

  • Concomitant use with strong CYP3A4 inhibitors (e.g., itraconazole, ketoconazole, clarithromycin, HIV protease inhibitors)
  • Concomitant use with cyclosporine, danazol, or gemfibrozil
  • Active liver disease or unexplained persistent elevations of serum transaminases
  • Pregnancy and breastfeeding
  • Hypersensitivity to simvastatin or any component of the formulation

Side Effects

  • Muscle pain, tenderness, or weakness (myalgia)
  • Elevated creatine kinase (CK)
  • Hepatotoxicity with elevated liver enzymes
  • Gastrointestinal disturbances (constipation, abdominal pain, flatulence)
  • Headache
  • Increased blood glucose levels
  • Rare but serious: rhabdomyolysis, immune-mediated necrotizing myopathy, hypersensitivity reactions including anaphylaxis

Interactions

  • Strong CYP3A4 inhibitors significantly increase simvastatin exposure and risk of myopathy
  • Cyclosporine, danazol, and gemfibrozil increase simvastatin exposure
  • Amiodarone, diltiazem, verapamil, and amlodipine increase simvastatin exposure when used with higher doses
  • Warfarin: monitor INR as simvastatin may potentiate anticoagulant effect
  • Grapefruit juice (especially large quantities) may increase simvastatin levels

Counseling Points

  • Take once daily in the evening for optimal effect
  • Report unexplained muscle pain, tenderness, weakness, or brown urine immediately
  • Avoid consuming large quantities of grapefruit juice
  • Continue dietary measures (low-fat, low-cholesterol diet) while taking medication
  • Regular monitoring of liver function tests and lipid profiles is necessary
  • Inform all healthcare providers about all medications being taken to avoid interactions