Can Myrbetriq and Toviaz Be Taken Together?
Yes, Myrbetriq (mirabegron) and Toviaz (fesoterodine) can be taken together, and this combination is explicitly supported by clinical guidelines and FDA labeling for patients with overactive bladder who do not respond adequately to monotherapy. 1, 2
Guideline-Based Recommendation
The 2019 AUA/SUFU guideline specifically addresses combination therapy for overactive bladder, stating that clinicians may consider combination therapy with an anti-muscarinic (like fesoterodine/Toviaz) and β3-adrenoceptor agonist (like mirabegron/Myrbetriq) for patients refractory to monotherapy (Evidence Strength Grade B) 1. This recommendation is based on robust clinical trial data demonstrating improved efficacy without significant safety concerns compared to monotherapy.
FDA-Approved Combination
The FDA label for Myrbetriq explicitly includes data on combination therapy with antimuscarinic agents 2. In three 12-week studies involving 6,818 patients, combination treatment was evaluated and found to be safe and effective. The most common adverse reactions with combination therapy (>2% and exceeding monotherapy) were:
- Dry mouth (7.2-9.3% vs 3.6-6.5% with monotherapy)
- Urinary tract infections (4.0-7.0%)
- Constipation (3.9-4.2%)
- Tachycardia (0.9-2.2%)
Drug-Drug Interaction Profile
The pharmacokinetic interaction between these medications is minimal and clinically insignificant 3. Physiologically-based pharmacokinetic modeling demonstrates that when fesoterodine 8 mg is coadministered with mirabegron 50 mg, the active metabolite (5-HMT) exposure increases by only approximately 20% (AUC ratio 1.22-fold, Cmax ratio 1.17-fold). This modest increase does not require dose adjustment when both drugs are used within approved daily-dose ranges 3.
The mechanism: Mirabegron is a moderate CYP2D6 inhibitor and weak CYP3A inhibitor, while fesoterodine's active metabolite (5-HMT) is metabolized via both CYP2D6 and CYP3A pathways. Despite this overlap, the interaction remains clinically insignificant.
Clinical Efficacy Evidence
Animal and human studies support additive or synergistic effects when combining these agents 4. The combination demonstrates:
- Greater improvements in bladder capacity than either drug alone
- Enhanced reduction in urgency episodes
- Improved quality of life scores
- Effect sizes that appear additive rather than merely cumulative
Important Caveats
Monitor for urinary retention, particularly in patients with:
- Bladder outlet obstruction
- Benign prostatic hyperplasia
- Pre-existing voiding difficulties
The FDA label notes that urinary retention events were reported more frequently with combination therapy compared to monotherapy 2. The most frequent adverse reactions leading to discontinuation (≥0.2%) were dry mouth and urinary retention.
Blood pressure monitoring is recommended, as mirabegron can increase blood pressure 2. This effect is not significantly altered by combination therapy but remains a consideration for all patients on mirabegron.
Practical Implementation
Start both medications at standard doses:
- Mirabegron 25-50 mg once daily
- Fesoterodine 4-8 mg once daily
No dose adjustment is required when initiating combination therapy. Patients should be counseled about the increased likelihood of antimuscarinic side effects (dry mouth, constipation) compared to β3-agonist monotherapy, though these remain generally well-tolerated 1, 2.