Generic Name

Myrbetriq

Mechanism

Myrbetriq binds to β3‑adrenergic receptors in the detrusor smooth muscle of the bladder.
• ↑ intracellular cAMP → smooth‑muscle relaxation during the storage phase
• ↑ bladder capacity & compliance
• ↓ urethral sphincter tone during voiding (minimal effect)
• No anticholinergic activity → fewer dry‑mouth or constipation side‑effects

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Pharmacokinetics

• Route: Oral tablets
• Absorption: ~50 % oral bioavailability; peak plasma concentration (Tmax) 4–5 h
• Distribution: Protein‑binding ~30 %
• Metabolism: Primarily cytochrome‑P450 (CYP 3A4, CYP 2D6, CYP 2C9); active metabolites contribute <10 % of activity
• Elimination: 70 % renal excretion (unchanged drug + metabolites); 30 % hepatic
• Half‑life: ~50 h (steady‑state achieved in ~2 weeks)

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Indications

• Adults with overactive bladder (symptoms: urgency, frequency, urge‑incontinence)
• Can be used as first‑line or add‑on therapy if antimuscarinics are poorly tolerated

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Contraindications

• Hypersensitivity to *mirabegron* or any component
• Severe uncontrolled hypertension (≥180/110 mm Hg)
• Pregnancy: category B; avoid if possible
• Renal impairment: dose adjustment if CrCl <30 mL/min (see dosing)
• Ocular hypertension or narrow angle glaucoma – monitor intraocular pressure

Warnings
• Can raise systemic blood pressure; monitor especially in the first 4 weeks
• May impair lower‑extremity venous return in patients with chronic venous disease
• Potential interaction with CYP3A4 inhibitors/inducers: increase/decrease plasma concentrations

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Dosing

• Oral ingestion with or without food
• Take at the same time each day
• Advise patients to stay upright for 2–3 h post‑dose to reduce syncope risk

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Adverse Effects

Common (≥ 10 % incidence)
• Hypertension (systolic ↑ > 10 mm Hg)
• Nasopharyngitis
• Urinary retention (especially in patients with benign prostatic hyperplasia)

Serious (≤ 1 % incidence)
• Ocular hypertension / angle‑closure glaucoma
• Symptomatic hypotension (rare)
• Severe allergic reactions (angioedema, anaphylaxis)
• Cardiovascular events (QT prolongation in susceptible individuals)

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Monitoring

• Blood pressure: baseline & 2–4 weeks after initiation; continue annually
• Renal function: creatinine & eGFR baseline, at 8 weeks, then annually or with clinical changes
• Intraocular pressure: baseline & 8 weeks if glaucoma risk factors present
• Urinalysis: for urinary retention symptoms
• Adverse event review: at each follow‑up visit (≥ 4 weeks)

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Clinical Pearls

• Switching from antimuscarinics: patients with dry‑mouth or constipation may transition to *Myrbetriq* for improved tolerability.
• Combination therapy: add‑on to antimuscarinics is approved for refractory OAB; monitor for additive BP rise.
• Elderly & renal: start low and titrate slowly; check renal function before increasing dose.
• Drug interactions: avoid concomitant use with strong CYP 3A4 inhibitors (itraconazole, clarithromycin) or inducers (rifampin); dose adjustment may be necessary.
• Ocular risk: screen patients with a history of narrow angles or glaucoma; obtain baseline and periodic IOP checks.
• Patient education: counsel on the potential for transient BP elevation and to report sudden headache, vision changes, or syncope promptly.

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• Key Takeaway: *Myrbetriq* offers a non‑anticholinergic alternative to treat overactive bladder, expanding therapeutic options, especially for patients intolerant to or contraindicated for classic antimuscarinics.