ZOCOR may cause myopathy and rhabdomyolysis. Acute kidney injury secondary to myoglobinuria and rare fatalities have occurred as a result of rhabdomyolysis in patients treated with statins, including ZOCOR.

In clinical studies of 24,747 ZOCOR-treated patients with a median follow-up of 4 years, the incidence of myopathy, defined as unexplained muscle weakness, pain, or tenderness accompanied by creatinine kinase (CK) increases greater than ten times the upper limit of normal (10xULN), were approximately 0.03%, 0.08%, and 0.61% in patients treated with ZOCOR 20 mg, 40 mg, and 80 mg daily, respectively. In another clinical study of 12,064 ZOCOR-treated patients (with a history of myocardial infarction) with a mean follow-up of 6.7 years, the incidences of myopathy in patients taking ZOCOR 20 mg and 80 mg daily were approximately 0.02% and 0.9%, respectively. The incidences of rhabdomyolysis (defined as myopathy with a CK >40xULN) in patients taking ZOCOR 20 mg and 80 mg daily were approximately 0% and 0.4%, respectively [see Adverse Reactions (6.1)].

Risk Factors for Myopathy

Risk factors for myopathy include age 65 years or greater, uncontrolled hypothyroidism, renal impairment, concomitant use with certain other drugs (including other lipid-lowering therapies), and higher ZOCOR dosage; Chinese patients on ZOCOR may be at higher risk for myopathy [see Contraindications (4), Drug Interactions (7.1), and Use in Specific Populations (8.8)]. The risk of myopathy is increased by elevated plasma levels of simvastatin and simvastatin acid. The risk is also greater in patients taking an 80 mg daily dosage of ZOCOR compared with patients taking lower ZOCOR dosages and compared with patients using other statins with similar or greater LDL-C-lowering efficacy [see Adverse Reactions (6.1)]. 

Steps to Prevent or Reduce the Risk of Myopathy and Rhabdomyolysis

The concomitant use of strong CYP3A4 inhibitors with ZOCOR is contraindicated. If short-term treatment with strong CYP3A4 inhibitors is required, temporarily suspend ZOCOR during the duration of strong CYP3A4 inhibitor treatment. The concomitant use of ZOCOR with gemfibrozil, cyclosporine, or danazol is also contraindicated [see Contraindications (4) and Drug Interactions (7.1)].

ZOCOR dosage modifications are recommended for patients taking lomitapide, verapamil, diltiazem, dronedarone, amiodarone, amlodipine or ranolazine [see Dosage and Administration (2.5)]. ZOCOR use should be temporarily suspended in patients taking daptomycin. Lipid modifying doses (≥1 gram/day) of niacin, fibrates, colchicine, and grapefruit juice may also increase the risk of myopathy and rhabdomyolysis [see Drug Interactions (7.1)].

Use the 80 mg daily dosage of ZOCOR only in patients who have been taking simvastatin 80 mg daily chronically without evidence of muscle toxicity [see Dosage and Administration (2.1)]. If patients treated with an 80 mg daily dosage of ZOCOR are prescribed an interacting drug that increases the risk for myopathy and rhabdomyolysis, switch to an alternate statin [see Drug Interactions (7.1)]. 

Discontinue ZOCOR if markedly elevated CK levels occur or if myopathy is either diagnosed or suspected. Muscle symptoms and CK increases may resolve if ZOCOR is discontinued. Temporarily discontinue ZOCOR in patients experiencing an acute or serious condition at high risk of developing renal failure secondary to rhabdomyolysis, e.g., sepsis; shock; severe hypovolemia; major surgery; trauma; severe metabolic, endocrine, or electrolyte disorders; or uncontrolled epilepsy.

Inform patients of the risk of myopathy and rhabdomyolysis when starting or increasing the ZOCOR dosage and advise patients receiving an 80 mg daily dosage of ZOCOR of the increased risk of myopathy and rhabdomyolysis. Instruct patients to promptly report any unexplained muscle pain, tenderness or weakness, particularly if accompanied by malaise or fever.