Does statin therapy initiation increase the risk for myopathy? An observational study of 32,225 diabetic and nondiabetic patients.

BACKGROUND: Estimates of myopathy rates in the literature are based on adverse events reported in clinical trials, which may not be representative of the clinical practice setting.

OBJECTIVE: The objective of this study was to estimate the prevalence of myopathic events, particularly myalgia, myositis, and rhabdomyolysis in a community-based practice among a cohort of subjects with or without diabetes, some of whom received statin treatment.

METHODS: In this retrospective data analysis, we identified members of a health maintenance organization (HMO) who initiated statin treatment between 1997 and 2004 and classified them into 2 groups: those subjects with diabetes and those without. We matched them to an equal number of health plan members based on age group, diabetes diagnosis, and year of health plan enrollment. We defined 4 levels of myopathic events according to the American College of Cardiology, the American Heart Association, and the National Heart, Lung, and Blood Institute's definitions as follows: myalgia, mild myositis, severe myositis, and rhabdomyolysis. Subjects were observed for approximately 9 years. Prevalence rates were calculated by adjusting for known myopathic risk factors and also by utilizing Cox regression models to identify predictors of time for myopathic events.

RESULTS: Of the 35,413 HMO members initially assessed for inclusion, 32,225 were identified and classified into the 2 cohorts: diabetes (n = 10,247) and nondiabetes (n = 21,978). A greater proportion of statin initiators in both the diabetes (7.9% vs 5.5%; P < 0.001) and nondiabetes cohorts (9.0% vs 3.7%; P < 0.001) experienced myopathic events. However, 95% of events were myalgia or mild myositis. The prevalence of severe myositis was 0.4 per 1000 person-years (95% CI, 0.2-0.7) and 0.8 per 1000 person-years (95% CI, 0.6-1.1) among statin initiators with or without diabetes, respectively. By comparison, rates were 0.3 (95% CI, 0.1-0.5) and 0.2 (95% CI, 0.1-0.4) per 1000 person-years among nonstatin users with or without diabetes, respectively. Rates of rhabdomyolysis were 0.1 (95% CI, 0.1-0.3) and 0.2 (95% CI, 0.1-0.5) per 1000 person-years among statin and non-statin users with diabetes, respectively, and 0.2 (95% CI, 0.1-0.4) in both groups without diabetes.

CONCLUSIONS: Statin initiation was associated with an approximate doubling of the risk for any myopathic event but did not appear to be associated with an increased risk for rhabdomyolysis in these patients. Because clinically significant elevations of creatine kinase levels were rare, statins appeared to be well tolerated in diabetic and nondiabetic patients who used them.