What is the best course of treatment for a 70-year-old female patient with occasional left flank pain, symptoms of Overactive Bladder (OAB), and irritative voiding, who is currently taking Myrbetriq (Mirabegron) 25mg, using diapers, and has a Urinalysis (UA) showing pyuria and E coli 100K sensitive to Macrobid (Nitrofurantoin), with a Post Void Residual (PVR) of 17mL and a normal Pelvic sonogram?

Treatment of UTI and Management of OAB in a 70-Year-Old Female

Treat the E. coli UTI immediately with nitrofurantoin 5 days, discontinue Myrbetriq during treatment, and reassess OAB symptoms after infection resolution before proceeding with cystoscopy and urodynamics. 1

Immediate Priority: Treat the Urinary Tract Infection

The documented pyuria and E. coli 100K colony count represents an active UTI that must be treated before any further OAB evaluation or management. 1

Antibiotic Selection and Duration

• Prescribe nitrofurantoin for 5 days as first-line therapy for uncomplicated cystitis in women, given the documented macrobid sensitivity 1
• This represents the shortest effective duration consistent with current guidelines for uncomplicated bacterial cystitis 1
• Alternative regimens include trimethoprim-sulfamethoxazole for 3 days or fosfomycin as a single dose, but nitrofurantoin 5 days is appropriate given confirmed susceptibility 1

Critical Management Decision: Discontinue Myrbetriq During UTI Treatment

Stop Myrbetriq immediately and do not restart until after UTI resolution and symptom reassessment. 1, 2

• The irritative voiding symptoms (urgency, frequency) may be entirely or partially attributable to the UTI rather than OAB 1, 2, 3
• Continuing beta-3 agonist therapy during active infection provides no benefit and prevents accurate assessment of true OAB symptoms 2, 3
• UTI must be excluded before diagnosing or treating OAB, as it is a key differential diagnosis 1, 2, 3

Post-UTI Treatment Reassessment Strategy

Timing of Follow-Up

• Schedule follow-up 2-3 weeks after completing antibiotics (not the originally planned 2 weeks from initial visit) to allow complete resolution of infection-related inflammation 1
• This timing allows differentiation between UTI-related symptoms and true OAB symptoms 1, 2

Symptom Reassessment Protocol

At the post-treatment visit, systematically evaluate whether irritative symptoms persist, improve, or resolve: 1, 2, 3

• If symptoms completely resolve: The "OAB" was likely UTI-related; no further OAB treatment needed, but investigate recurrent UTI risk factors 1
• If symptoms significantly improve but remain bothersome: Consider restarting Myrbetriq or alternative OAB therapy 1
• If symptoms persist unchanged: Proceed with planned cystoscopy and urodynamics as originally scheduled 1

Additional Diagnostic Considerations for This Patient

Post-Menopausal Risk Factors Present

This 70-year-old female has multiple risk factors for both recurrent UTI and OAB that require evaluation: 1

• Urinary incontinence (using diapers) increases recurrent UTI risk 1
• Post-menopausal status with potential atrophic vaginitis 1
• The normal PVR of 17 mL appropriately excludes urinary retention as a contributing factor 1

Left Flank Pain Requires Attention

The occasional left flank pain warrants imaging if not already completed, particularly given the UTI: 1

• Ultrasound should be performed to exclude urolithiasis or upper tract involvement, especially with history of flank pain and current UTI 1
• Flank pain with UTI raises concern for possible pyelonephritis rather than simple cystitis, which would require longer antibiotic duration 1
• If pyelonephritis is suspected clinically (fever, costovertebral angle tenderness), switch to fluoroquinolone 5-7 days or trimethoprim-sulfamethoxazole 14 days based on susceptibility 1

Future OAB Management if Symptoms Persist Post-UTI

First-Line Behavioral Interventions

If OAB symptoms persist after UTI resolution, restart with behavioral therapies before resuming pharmacotherapy: 1, 2

• Bladder training and pelvic floor muscle exercises are as effective as antimuscarinic medications and should be first-line 1
• Fluid management with 25% reduction in intake reduces frequency and urgency 1
• Caffeine reduction improves voiding frequency 1
• Weight loss of 8% reduces urgency incontinence episodes by 42% versus 26% in controls 1

Pharmacotherapy Reconsideration

If behavioral therapies alone are insufficient, consider these options: 1, 2, 4

• Restart Myrbetriq 25 mg (current dose) or increase to 50 mg if 25 mg was inadequate 4
• Mirabegron 50 mg demonstrates significant efficacy within 4 weeks for incontinence episodes, micturition frequency, and urgency 4, 5, 6
• Mirabegron 25 mg shows effectiveness within 8 weeks 4
• Combination therapy with behavioral interventions and Myrbetriq provides optimal outcomes 1, 2
• Alternative: Switch to antimuscarinic agents (darifenacin, fesoterodine, oxybutynin, solifenacin, tolterodine, trospium) as second-line pharmacotherapy 1

Safety Monitoring for Myrbetriq

Monitor blood pressure if restarting Myrbetriq, particularly in this elderly patient: 4, 6

• Hypertension is the most common adverse event with mirabegron 4, 6
• Check blood pressure at follow-up visits while on therapy 4
• The normal PVR of 17 mL indicates no concern for urinary retention with beta-3 agonist therapy 1, 4

Critical Pitfall to Avoid

The most dangerous error would be continuing or restarting Myrbetriq before UTI resolution and symptom reassessment. 1, 2, 3

• This would mask the true cause of irritative symptoms and potentially delay recognition of complicated UTI 1
• It would prevent accurate determination of whether OAB symptoms are genuine or infection-related 1, 2, 3
• Proceeding with cystoscopy and urodynamics during active infection risks introducing bacteria into the upper urinary tract and provides unreliable results 1

Recurrent UTI Prevention Strategy

If this represents recurrent UTI (≥3 episodes in 12 months), implement prevention measures: 1

• Counsel on adequate hydration, urge-initiated voiding, and post-coital voiding 1
• Consider topical vaginal estrogen for post-menopausal atrophic vaginitis 1
• Methenamine hippurate reduces recurrent UTI episodes in women without urinary tract abnormalities (strong recommendation) 1
• Reserve antimicrobial prophylaxis only after non-antimicrobial interventions fail 1