Links Found Between High-Dose Simvastatin and Myopathy

Recently, Merck announced that it would be making changes to the prescribing information for its drugs Zocor (simvastatin) and Vytorin (ezetimine/simvastatin) after recent studies linked it to an increased risk of myopathy, including rhabdomyolysis. The increased risk of myopathy was found in those who were using simvastatin 80 mg compared with both lower doses of the drug and other similarly effective statin therapies. Risk was found to be highest during the first year of treatment with noticeable decreases after. Drug interaction was also considered in the new prescribing information, and concommitnent use of strong cytochrome P450 3A4 inhibitors, gemfibrozil, cyclosporine, and danazol is contradicted. The dose caps for other drugs used in conjunction with simvastatin were changed as well, with amiodarone, verapamil, and diltiazem not being used in excess of 10 mg and amlodipine and ranolazine not being used in more than 20 mg doses. The prescribing information also recommends that the 80 mg doses of simvastatin be restricted to those patients who have already been taking the dose chronically, for more than 12 months, and have shown no evidence of muscle toxicity.

These changes were made after findings from the Study of Effectiveness of Additional Reductions in Cholesterol and Homocysteine (SEARCH) and others. The SEARCH clinical trial showed that the increase of myopathy, or unexplained muscle weakness or pain with serum creatine kinase, to be ten times the upper limit of normal in significantly more patients taking 80 mg doses of simvastatin than those taking 20 mg doses. Te risk for rhambdomyolysis, or myopathy with serum creatine kinase more than 40 times the upper limit of normal, was also seen in significant increases.

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