Simvastatin Drug Interactions

Drug interactions may alter the way simvastatin (Zocor, Simvacor) works or possibly increase the risk of adverse effects. To prevent serious side effects, it is important to learn about the different drugs that can potentially interact with this medication.

There are a total of 208 drugs that are known to interact with simvastatin. Of this number, 60 drugs cause major drug interactions while the rest result in moderate side effects. Basically, these drugs affect the metabolism of simvastatin, either causing an increase or a decrease in serum levels. This change in drug levels in the blood may increase the risk for side effects or cause a reduction in the desired pharmacologic action of the simvastatin.

Significant Drug Interactions

Some of the drugs that can cause significant drug interactions include the following:

CYP3A4 Inhibitors - These drugs can significantly affect the CYP3A4 metabolic pathway where simvastatin and other cholesterol-lowering drugs are metabolized. Taking these medications together with simvastatin can lead to increased simvastatin levels in the blood which increase the risk of muscular side effects and rhabdomyolysis (a rare and potentially life-threatening muscular condition), particularly in patients taking higher doses of simvastatin.

Because of the potential adverse effects, antifungals, danazol and cyclosporine are contraindicated in patients taking simvastatin. In case use of such medications is unavoidable, simvastatin therapy may be suspended throughout the treatment. Drugs that affect the CYP3A4 metabolic pathway include:

• danazol (Danocrine)
• cyclosporine (Sandimmune)
• Antifungals
  • itraconazole (Sporanox)
  • ketoconazole (Nizoral)
  • posaconazole (Noxafil)
• Antibiotics
  • erythromycin (E-mycin)
  • clarithromycin (Biaxin)
  • telithromycin (Ketek)

Other Cholesterol-Lowering Drugs – These medications increase the risk of muscular side effects or myopathy when taken together with simvastatin, therefore are contraindicated.

• gemfibrozil (Lopid)
• Niacin and niacin-containing products
• Other fibrates

Calcium-Channel Blockers and Anti-Anginal Drugs: These medications are used to manage abnormal heart rhythm and chest pain. Concomitant use of these drugs increase the risk of myopathy as well as rhabdomyolysis.

• ranolazine (Ranexa)
• Calcium Channel Blockers
  • verapamil (Calan, Isoptin)
  • diltiazem (Cardizem, Cartia)
  • amlodipine (Norvasc)

Anti-Arrhythmic Drugs: These medications are used to treat irregular heartbeat. Concomitant use of amiodarone and simvastatin increases the risk of muscular side effects. Meanwhile, taking digoxin together with simvastatin may result in a slight increase in the digoxin levels in the blood and possible changes in heart rhythm.

• amiodarone (Cordarone)
• digoxin (Lanoxin)

Anticoagulant Drugs: These medications are used to prevent formation of blood clots. Simvastatin potentiates the pharmacologic effect of Coumadin thereby increasing the risk of bleeding. Patients taking these medications together should be carefully monitored for signs of bleeding. Diagnostic tests, particularly prothrombin time determination, may be recommended to prevent serious side effects.

• warfarin (Coumadin)

Anti-Gout Agent: This medication is used for the management of gout. Concomitant use of simvastatin and colchicines increase the risk of myopathy, including rhabdomyolsis. Caution should be taken when using these drugs together.

• Colchicine

Grapefruit products including grapefruit, grapefruit juice and grapefruit-containing health supplements should also be avoided while on simvastatin treatment.

This medication guide does not contain all medications that can potentially interact with simvastatin. It is recommended that patients avoid taking any other medications without consulting their healthcare provider.