Does Fesoterodine Exacerbate UTIs?
Yes, fesoterodine is associated with an increased incidence of urinary tract infections (UTIs) compared to both placebo and tolterodine, though this does not represent a true "exacerbation" of existing UTIs but rather an increased occurrence of new UTI events as an adverse effect of the medication.
Evidence from High-Quality Guidelines
The American College of Physicians' 2014 clinical practice guideline provides the strongest evidence on this question, based on moderate-quality data from comparative trials:
- Fesoterodine causes more UTIs than tolterodine, along with dry mouth and headache, when comparing the two antimuscarinics head-to-head 1
- The number needed to harm (NNTH) for any adverse event with fesoterodine versus tolterodine is 18 (95% CI 11-52), meaning for every 18 patients treated with fesoterodine instead of tolterodine, one additional patient will experience an adverse event including UTI 1
Clinical Trial Data on UTI Incidence
Multiple Phase III trials have documented UTI as a treatment-emergent adverse effect with fesoterodine:
- UTI was among the most common adverse events reported with fesoterodine treatment in randomized controlled trials, alongside dry mouth, constipation, and headache 2, 3
- In the pivotal 12-week trials involving over 1,900 patients, urinary tract infection occurred more frequently with fesoterodine than placebo 3
- The mechanism appears related to antimuscarinic effects on bladder function rather than direct infection promotion 4
Comparative Context with Other Antimuscarinics
Understanding fesoterodine's UTI risk requires comparison to other agents in this drug class:
- Oxybutynin also causes more UTIs than tolterodine, suggesting this may be a class effect that varies in magnitude between different antimuscarinics 5
- The American Heart Association guidelines note that fesoterodine's UTI risk is specifically elevated compared to tolterodine, making tolterodine a potentially safer alternative when UTI risk is a concern 6
Clinical Implications and Risk Mitigation
When prescribing fesoterodine, clinicians should:
- Counsel patients about UTI symptoms (dysuria, frequency, urgency beyond baseline OAB symptoms, fever, suprapubic pain) and instruct them to report these promptly 7
- Consider starting with fesoterodine 4 mg rather than 8 mg, as adverse events including UTI increase with higher doses 8
- Evaluate baseline UTI risk factors before initiating therapy, including history of recurrent UTIs, incomplete bladder emptying, or anatomic abnormalities 7
- Monitor post-void residual urine volume, as antimuscarinic-induced urinary retention can predispose to UTI 3
Important Caveats
The increased UTI incidence with fesoterodine represents new infection events occurring during treatment, not worsening of pre-existing UTIs. The antimuscarinic mechanism may impair complete bladder emptying, creating conditions favorable for bacterial growth 4. However, this does not contraindicate fesoterodine use—rather, it requires informed patient selection and monitoring.
If a patient develops a UTI while on fesoterodine, treat the infection with appropriate antimicrobials per standard guidelines (empiric therapy for uncomplicated UTI, culture-directed therapy for complicated cases) 7. The decision to continue or discontinue fesoterodine should be based on symptom control benefit versus recurrent UTI risk, potentially considering alternative agents like mirabegron (a beta-3 agonist without antimuscarinic effects) if UTIs become problematic 1.