What are the dosing guidelines for mirabegron (Myrbetriq) oral suspension 8 mg/mL in adults and children, and what is its approved indication?

Mirabegron 8mg/mL Dosing and Indication

Mirabegron 8mg/mL oral suspension (MYRBETRIQ Granules) is FDA-approved exclusively for neurogenic detrusor overactivity (NDO) in pediatric patients aged 3 years and older, with weight-based dosing starting at the time of dispensing and requiring reconstitution with 100mL water. 1

Approved Indication

The 8mg/mL oral suspension formulation is indicated only for NDO in pediatric patients aged 3 years and older—it is NOT approved for overactive bladder (OAB) in adults. 1 For adult OAB, only the extended-release tablets (25mg or 50mg) are approved, either as monotherapy or in combination with solifenacin succinate. 1

Dosing Guidelines for Pediatric NDO

Weight-Based Dosing Algorithm

For pediatric patients weighing less than 35 kg:

• Must use MYRBETRIQ Granules (8mg/mL suspension) exclusively
• Starting dose is weight-based (specific weight bands not provided in evidence but referenced in FDA label)
• After 4-8 weeks, increase to the lowest effective dose without exceeding maximum recommended dose
• Administer once daily with food 1

For pediatric patients weighing 35 kg or more:

• May use either MYRBETRIQ tablets OR MYRBETRIQ Granules (not interchangeable)
• If using tablets: Start 25mg once daily, may increase to 50mg after 4-8 weeks
• If using oral suspension: Start 6mL (48mg) once daily, may increase to maximum 10mL (80mg) after 4-8 weeks
• Take with food 1

Critical Dosing Caveats

Do not substitute tablet and suspension formulations on a milligram-per-milligram basis—they are pharmacokinetically distinct products. 1 Never combine both formulations to achieve total dose. A recommended adult dosage for MYRBETRIQ Granules has not been determined. 1

Preparation and Storage

• Reconstitute at time of dispensing by adding 100mL water to bottle
• Shake vigorously for 1 minute, let stand 10-30 minutes, shake again for 1 minute
• Final concentration: 8mg/mL
• Store at 20-25°C (68-77°F) for maximum 28 days after reconstitution
• Discard unused portion after 28 days 1

Dose Adjustments for Renal/Hepatic Impairment

Pediatric patients ≥35 kg with renal impairment (using oral suspension):

• eGFR ≥30 mL/min/1.73m²: Start 6mL (48mg), max 10mL (80mg)
• eGFR 15-29 mL/min/1.73m²: Start 6mL (48mg), max 6mL (48mg)
• eGFR <15 mL/min/1.73m² or dialysis: Not recommended 1

Pediatric patients ≥35 kg with hepatic impairment (using oral suspension):

• Child-Pugh Class A (mild): Start 6mL (48mg), max 10mL (80mg)
• Child-Pugh Class B (moderate): Start 6mL (48mg), max 6mL (48mg)
• Child-Pugh Class C (severe): Not recommended 1

Administration Requirements

• Must be taken with food in pediatric patients to reduce potential exposure-related risks 1
• Use appropriate dosing device provided
• Swallow tablets whole if using tablet formulation—do not chew, divide, or crush 1

Safety Monitoring

Monitor blood pressure periodically, especially in hypertensive patients. Blood pressure increases may be larger in children (3 to <12 years) than adolescents (12 to <18 years). 1 Not recommended in severe uncontrolled hypertension (systolic ≥180 mmHg and/or diastolic ≥110 mmHg). 1

Administer with caution in patients with bladder outlet obstruction or those taking muscarinic antagonists due to urinary retention risk. 1

Missed Dose Protocol

Take missed dose as soon as remembered, unless more than 12 hours have passed. If >12 hours, skip the missed dose and resume usual schedule. 1