5-alpha reductase inhibitors and the risk of anaemia among men with benign prostatic hyperplasia: A population-based cohort study

5-alpha reductase inhibitors (5 alpha RIs) are effective for the treatment of benign prostatic hyperplasia (BPH). However, 5 alpha RIs could lower levels of haemoglobin, increasing the risk of anaemia. The objective of this study was to compare the rate of anaemia between new users of 5 alpha RIs and alpha-blockers in the UK. Methods: We conducted a matched, active comparator, new-user cohort study using the Clinical Practice Research Datalink. The study population consisted of men aged >= 40 years with incident BPH who initiated 5 alpha RIs between 1998 and 2019 and were matched 1:1 on propensity score to new users of alpha-blockers. Anaemia was defined by a measured haemoglobin <130 g/L. We used Cox proportional hazards models to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for anaemia. Results: Our study cohort included 9429 new users of 5 alpha RIs and 9429 matched new users of alpha-blockers. Their median durations of follow-up were 136 days (interquartile range: 54-336 d) and 77 days (interquartile range: 58-236 d), respectively. A total of 2865 5 alpha Rls users and 2407 alpha-blocker users developed incident anaemia, representing rates of 37.3 (95% CI: 33.6-41.3) and 42.0 (95% CI: 38.1-46.2) per 100 person-years, respectively. The use of 5 alpha RIs was not associated with an increased risk of anaemia compared to the use of alpha-blockers (HR: 0.95, 95% CI: 0.90-1.00). Similarly, we did not observe an increased risk of mild, moderate, or severe anaemia. Conclusion: The use of 5 alpha RIs was not associated with an increased risk of anaemia compared to the use of alpha-blockers among men with BPH.