Mirabegron Does Not Exacerbate UTIs
Mirabegron does not exacerbate urinary tract infections (UTIs); in fact, UTIs are listed as a common adverse event that occurs at similar rates to placebo, indicating they are part of the natural disease course in overactive bladder patients rather than a drug-induced complication. 1, 2, 3
Evidence from Clinical Trials
The safety profile of mirabegron from multiple Phase III trials demonstrates that UTIs occur as a background event in the overactive bladder population, not as a consequence of the medication:
In adults with overactive bladder, urinary tract infection was reported as one of the most common adverse events, but occurred at rates similar to placebo groups, indicating no causal relationship with mirabegron treatment 1, 2
The 12-week randomized controlled trial involving patients receiving 50 mg or 100 mg mirabegron daily showed that UTI incidence was comparable across placebo and treatment groups 2
Long-term safety data up to 12 months confirmed that urinary tract infection remained among the most frequently reported adverse events but did not show increased incidence with mirabegron compared to baseline expectations in this patient population 3
Mechanism Considerations
The pharmacologic action of mirabegron actually argues against UTI exacerbation:
Mirabegron works as a β3-adrenoceptor agonist that relaxes the detrusor muscle during bladder filling, enhancing storage function without impairing voiding mechanics 4, 5
Unlike antimuscarinics, mirabegron does not cause significant increases in post-void residual volume, which would theoretically increase UTI risk 4
Important Caveat: Urinary Retention Risk
While mirabegron does not exacerbate UTIs directly, there is one scenario requiring vigilance:
Patients with bladder outlet obstruction or those taking other overactive bladder medications may develop urinary retention when starting mirabegron, and incomplete bladder emptying could theoretically predispose to UTIs 1
The FDA label specifically warns that mirabegron may increase chances of inability to empty the bladder in patients with bladder outlet obstruction 1
Monitor for urinary retention by assessing post-void residual volume, particularly in men with BPH or patients with known voiding difficulties 6, 4
Clinical Bottom Line
UTIs reported in mirabegron trials represent the baseline infection rate in overactive bladder patients, not a drug-induced complication 2, 3
The primary urologic safety concern with mirabegron is urinary retention in susceptible patients (those with outlet obstruction), not UTI exacerbation 1
If a patient develops recurrent UTIs while on mirabegron, investigate other causes (incomplete emptying, anatomic abnormalities, behavioral factors) rather than attributing it to the medication itself 1