In a 75-year-old female with overactive bladder symptoms, should I start Tovias (trospium chloride) or Myrbetriq (mirabegron)?

Myrbetriq (Mirabegron) Over Tovias (Trospium) for a 75-Year-Old Female with OAB

For a 75-year-old female with overactive bladder symptoms, I recommend starting with Myrbetriq (mirabegron) over Tovias (trospium chloride) due to its superior tolerability profile, particularly regarding anticholinergic side effects that pose greater risks in elderly patients.

Rationale for Mirabegron as First-Line Pharmacotherapy

Efficacy Considerations

Both medications demonstrate similar efficacy for OAB symptoms. The ACP guidelines indicate that pharmacologic agents are equally efficacious at managing urgency urinary incontinence, so the choice should be based on tolerability, adverse effect profile, ease of use, and cost 1. However, when efficacy is equivalent, the decision pivots entirely to safety—especially critical in a 75-year-old patient.

Critical Safety Advantages of Mirabegron in Elderly Patients

Mirabegron avoids anticholinergic burden, which is particularly important in elderly patients 2. The key safety distinctions include:

• Dry mouth: Occurs with six-fold higher incidence with antimuscarinics (like tolterodine) compared to mirabegron 25-50 mg over 12 weeks 2
• Constipation: Significantly less common with mirabegron compared to antimuscarinics 1
• Cognitive effects: Trospium, despite being a quaternary amine with limited CNS penetration, still carries anticholinergic properties. Mirabegron has a low incidence of CNS effects and does not contribute to anticholinergic burden 2
• No increased discontinuation risk: Unlike trospium, which shows higher discontinuation rates due to adverse effects (NNTH 56) compared to placebo 1, mirabegron demonstrates better tolerability

Specific Evidence in Elderly Populations

The FDA label for Myrbetriq specifically notes that no overall differences in safety or effectiveness were observed between patients younger than 65 years and those 65 years or older, with 9.9% of study participants being 75 years or older 3. This directly addresses your patient population.

A systematic review confirms mirabegron's effectiveness and safety profile, noting it is "effective, safe, and well tolerated" with particular advantages when anticholinergic side effects are a concern 4.

Important Clinical Caveats for This Patient

Before Prescribing Mirabegron:

• Blood pressure monitoring: Check baseline BP, as mirabegron can cause modest increases in blood pressure and heart rate 1
• Renal function: If eGFR 15-29 mL/min/1.73 m², limit dose to 25 mg daily 3
• Hepatic function: If Child-Pugh Class B, limit dose to 25 mg daily 3
• Contraindications: Severe uncontrolled hypertension (systolic ≥180 mmHg or diastolic ≥110 mmHg)

Dosing Strategy:

Start with mirabegron 25 mg once daily, which can be increased to 50 mg if needed and tolerated. The lower starting dose is prudent in elderly patients to assess tolerability 3.

Why Not Trospium?

While trospium has demonstrated efficacy in patients ≥75 years 5, it carries several disadvantages:

• Higher discontinuation rates due to adverse effects compared to placebo 1
• Anticholinergic side effects: Dry mouth, constipation, and blurred vision remain problematic 1
• Recent evidence suggests increased TEAE incidence compared to beta-3 agonists 6
• Twice-daily dosing for immediate-release formulation (though ER formulation is once-daily) may affect adherence

Essential First-Line Consideration

Before initiating any pharmacotherapy, ensure behavioral therapies have been attempted or are being implemented concurrently 1, 7. The ACP guidelines strongly recommend bladder training for urgency UI as first-line treatment (Grade: strong recommendation, moderate-quality evidence) 1. Pharmacotherapy should only be added if behavioral interventions are unsuccessful 1.

Behavioral Interventions to Implement:

• Bladder training with scheduled voiding
• Fluid management (avoid excessive intake, limit caffeine)
• If obese, weight loss counseling 1

Common Pitfall to Avoid

Do not assume all elderly patients tolerate antimuscarinics well simply because trospium has limited CNS penetration. The ACP guidelines specifically identify women aged >65 years as a vulnerable population and emphasize that "pharmacologic treatment should be based on harms, because most drugs are similarly efficacious" 1. The cumulative anticholinergic burden from trospium, even with its quaternary structure, combined with other medications this 75-year-old may be taking, poses unnecessary risk when a non-anticholinergic alternative exists.