Pharmacist Counseling Points for Switching from Solifenacin to Myrbetriq
When switching from solifenacin (an antimuscarinic) to Myrbetriq (mirabegron, a β3-adrenoceptor agonist), counsel patients that they will experience a different side effect profile—specifically, they should expect resolution of antimuscarinic effects like dry mouth and constipation, but need monitoring for blood pressure changes.
Key Mechanism and Expectation Differences
What's Changing
- Solifenacin works by blocking muscarinic receptors in the bladder, which commonly causes anticholinergic side effects
- Myrbetriq (mirabegron) relaxes the detrusor muscle through a completely different mechanism (β3-adrenoceptor agonism), avoiding anticholinergic effects 1
Expected Side Effect Changes
Anticholinergic effects will resolve:
- Dry mouth (common with solifenacin) should improve 2, 3
- Constipation (common with solifenacin) should improve 3
- Blurred vision should resolve
- Urinary retention risk decreases 3
New monitoring requirements with Myrbetriq:
- Blood pressure elevation is the primary concern—patients need BP monitoring, especially if they have hypertension history 1
- Nasopharyngitis (nasal/throat discomfort) may occur 1
- Urinary tract infections remain possible with both medications 1
Administration Instructions
Dosing Specifics
- Take once daily with water, swallow whole—do not crush, chew, or break the tablet 1
- Adults can take with or without food (unlike children who must take with food) 1
- Typical starting dose is 25 mg, may increase to 50 mg based on response 1
Missed Dose Protocol
- Take as soon as remembered unless more than 12 hours have passed since the scheduled dose 1
- If >12 hours, skip that dose and resume at the usual time—never double up 1
Safety Monitoring
Critical Warnings
Monitor blood pressure regularly—Myrbetriq can increase BP or worsen existing hypertension 1. This is the most clinically significant difference from solifenacin.
Watch for urinary retention—though less common than with antimuscarinics, it can still occur, especially in patients with bladder outlet obstruction 1
Seek immediate care for angioedema—swelling of lips, face, tongue, or throat with or without breathing difficulty requires emergency treatment 1
Drug Interactions
Inform prescriber if taking 1:
- Digoxin (Lanoxin)
- Thioridazine
- Flecainide or propafenone
- Notably: Can be safely combined with solifenacin if monotherapy proves insufficient 4
Efficacy Expectations
Symptom Improvement Timeline
- Both medications effectively reduce OAB symptoms 2, 3
- Mirabegron shows better tolerability with fewer treatment discontinuations due to side effects 2, 3
- Studies demonstrate significant improvement in urgency episodes, incontinence, and micturition frequency 3, 5
If Inadequate Response
Important counseling point: If Myrbetriq alone doesn't provide sufficient symptom control, combination therapy with solifenacin is an evidence-based option rather than abandoning either medication 4. The 2019 AUA/SUFU guidelines support combination therapy for refractory patients, with the SYNERGY and BESIDE trials demonstrating superior efficacy without significant additional safety concerns 4.
Special Populations
Contraindications and Precautions
- Avoid if allergic to mirabegron 1
- Use caution with liver or kidney problems 1
- Avoid with very high uncontrolled blood pressure 1
- Pregnancy/breastfeeding: Unknown safety—discuss with prescriber 1
Common Pitfalls to Avoid
- Don't assume similar side effects—patients expecting dry mouth/constipation need reassurance these will improve, but BP monitoring is now essential
- Don't crush tablets—extended-release formulation requires intact tablet 1
- Don't dismiss the option to add back solifenacin—combination therapy is evidence-based if monotherapy fails 4
- Don't overlook BP monitoring—this is the key safety difference from antimuscarinic therapy 1