What are the side effects of mirabegron (Myrbetriq)?

Side Effects of Mirabegron (Myrbetriq)

Mirabegron causes significantly less dry mouth and constipation than antimuscarinic medications, but carries important risks of hypertension (7.5-11.3%), cardiovascular effects including tachycardia, and nasopharyngitis. 1

Most Common Side Effects

The most frequently reported adverse reactions (>2% incidence and greater than placebo) include: 1

• Hypertension (7.5-11.3% incidence) - the most common side effect requiring periodic blood pressure monitoring, especially in patients with pre-existing hypertension 2, 1
• Nasopharyngitis (3.5-3.9%) 1, 3
• Urinary tract infection (2.9-4.2%) 1, 3
• Headache (2.1-3.2%) 1, 3
• Constipation (1.6%) - notably much lower than antimuscarinics 1
• Dry mouth (2.8% at 52 weeks) - significantly less frequent than with antimuscarinic drugs (8.6% for active control) 1, 4

Cardiovascular Effects

Mirabegron causes dose-dependent increases in blood pressure and heart rate that require clinical monitoring: 1, 5

• Blood pressure elevations occur predominantly in patients with baseline hypertension 1
• Tachycardia reported in 1.2-1.6% of patients 1
• Palpitations and cardiac arrhythmias can occur 1, 6
• Periodic blood pressure monitoring is essential, particularly in hypertensive patients 2, 7

Gastrointestinal Effects

Mirabegron demonstrates superior gastrointestinal tolerability compared to antimuscarinics: 8, 1

• Gastrointestinal disorders and nasopharyngitis are more frequent with mirabegron than placebo 8
• Dyspepsia, gastritis, and abdominal distension occur in <1% of patients 1
• Nausea and diarrhea (1.2-1.5%) 1

Serious but Rare Adverse Effects

Several potentially serious adverse reactions require awareness: 1

• Angioedema - if tongue, hypopharynx, or larynx involvement occurs, promptly discontinue mirabegron and ensure patent airway 1
• Urinary retention - monitor post-void residual volume, especially in men with lower urinary tract symptoms on combination therapy 2, 7
• Leukocytoclastic vasculitis, urticaria, and other skin reactions 1
• Nephrolithiasis (kidney stones) 1, 6
• Glaucoma 1

Hepatic Effects

Liver enzyme elevations can occur: 1

• GGT, AST, ALT, and LDH increases reported 1
• Two patients (0.3%) experienced >10-fold ALT/AST elevation that returned to baseline while continuing treatment 1

Drug Interaction-Related Side Effects

Mirabegron is a moderate CYP2D6 inhibitor, increasing systemic exposure to CYP2D6 substrates: 1, 5

• Appropriate monitoring and dose adjustment necessary for narrow therapeutic index drugs metabolized by CYP2D6 1
• Potential for additive adverse effects, particularly cardiac disorders, when combined with antimuscarinic drugs 6

Discontinuation Rates

Treatment discontinuation due to adverse effects varies by comparison: 8

• No statistically significant difference in discontinuation rates between mirabegron and placebo in some studies 8
• Most frequent adverse events leading to discontinuation (≥0.2%): nausea, headache, hypertension, diarrhea, constipation, dizziness, and tachycardia 1

Comparative Tolerability Profile

Mirabegron demonstrates significantly better tolerability than antimuscarinics for anticholinergic side effects: 4

• Significantly better tolerated regarding dry mouth than 21/22 active antimuscarinic comparators 4
• Significantly better tolerated for constipation than 9/20 antimuscarinic comparators 4
• Significantly better tolerated for urinary retention than 7/10 antimuscarinic comparators 4
• Unlike antimuscarinics, mirabegron does not produce significant anticholinergic effects from the start of treatment 2

Critical Safety Warning

Never crush mirabegron extended-release tablets - this causes immediate release of the entire 25 mg or 50 mg dose, leading to dangerously high peak plasma concentrations and increased risk of dose-related adverse effects including hypertension, tachycardia, and cardiovascular complications 9