Risk of rhabdomyolysis from 5‐α reductase inhibitors

PURPOSE: A recent regulatory warning and case reports have described the development of muscle complications with the use of 5-α reductase inhibitors (5ARIs). We wished to determine if there was a link between rhabdomyolysis and 5ARI usage. METHODS: We used a matched cohort design and linked administrative data from the province of Ontario, Canada, to investigate the risk of rhabdomyolysis in men using either finasteride or dutasteride. A total of 99 covariates were measured. We identified 93 197 men ≥66 years of age who initiated a new prescription for a 5ARI, and they were matched using a propensity score to an equal number of men not prescribed a 5ARI. RESULTS: New initiation of 5ARIs was not associated with a significantly increased risk of rhabdomyolysis (hazard ratio [HR] 1.21, 95% confidence interval [CI], 1.00-1.48, P = .06). When we examined the risk of rhabdomyolysis in the year prior to the initiation of a 5ARI, we found that men who would go on to use a 5ARI in the future had an elevated risk of rhabdomyolysis even prior to starting the medication (HR 1.31, 95% CI, 1.05-1.64, P = .01). Our secondary outcome of myositis and myopathy was significantly higher among 5ARI users (HR 1.63, 95% CI, 1.48-1.80, P < .01), and this risk was not present prior to 5ARI usage. CONCLUSION: 5-α reductase inhibitors do not appear to be associated with the development of rhabdomyolysis; however, they may be associated with an increased risk of myopathy and myositis.