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Risk of rhabdomyolysis from 5‐α reductase inhibitors

Abstract
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.