Statin and Statin-fibrate Use Was Significantly Associated with Increased Myositis Risk in a Managed Care Population

Objective: We quantified the risk of myositis associated with statin and fibrate drug use with other covariates within a managed care organization (MCO) population.

Study Design And Setting: The study spanned the years 1999-2003. Myositis cases had creatine kinase (CK) >or=10x upper limit of normal and a myopathy diagnosis. Exposures of statins, fibrates, and other drugs were assessed with age, gender, and indicators of suspected myopathy risk. Exposures were first analyzed within a cohort with CK monitoring and then within a more general secondary cohort. Adjusted relative risks (RRs) and incidence rates of myositis were generated by Poisson regression.

Results: Myositis was significantly associated with statin monotherapy (RR 2.8 [95% confidence interval, CI=1.3-5.9]), statin-fibrate combination therapy (9.1 [95% CI=3.5-23]), comorbid liver disease (4.3 [95% CI=1.5-13], and/or renal disease (2.5 [95% CI=1.3-5.0]). Myositis rates per covariate pattern ranged from 33 to 6,400 per 100,000 person-years. The mean time to event was 1.7 years for statin-fibrate use, 2.0 years for statins alone, and 2.1 years for unexposed. Within the secondary cohort, RRs increased up to 10 times further away from the null.

Conclusion: Statins, with or without fibrates, and liver and renal disease were significantly associated with increased myositis risk in an MCO population.