Myrbetriq (mirabegron) is an oral drug, developed by Astellas Pharma Inc., which is used for the treatment of overactive bladder syndrome (OAB), or the urgency to urinate.

According to the Multiple Sclerosis Trust, more than 75  percent of people with MS experience OAB, characterized by an increased urinary frequency (tendency to urinate often), nocturia (urinating at night), and incontinency (loss of bladder control causing urine leakage). OAB can occur in both male and female MS patients and affect their quality of life.

The clinical efficacy and safety of Myrbetriq have been assessed in multiple Phase 2 and Phase 3 clinical trials. The drug has now been approved for use in Japan (Betanis), Europe (Betmiga), and USA and Canada (Myrbetriq).

In MS, lesions may block or delay the nerve signals in the central nervous system (CNS) that control the bladder and the bladder opening (called sphincter). This may result in a combination of  overactivity in the detrusor muscle, or the smooth muscle found in the bladder wall, causing early filling, urgency to urinate, and incontinence, and an absence of coordination between the detrusor muscle and the sphincter, causing impaired bladder emptying.

Mechanism of Action of Myrbetriq

Myrbetriq belongs to a class of drugs called β3-adrenoreceptor agonists, which activate a receptor on the detrusor muscle causing its relaxation. It is an antispasmodic, meaning that it suppresses muscle spasms and relaxes the bladder muscles. This increases the capacity of the bladder to hold more urine for a longer period of time, preventing urgent, frequent or uncontrolled urination.

Drug Dosage and Side Effects

Myrbetriq is given orally in a tablet form for extended release (long-action). The recommended starting dose for the treatment of OAB is 25 mg once daily, which could be increased to 50 mg depending on the patient response. It is advised to swallow the whole tablet without crushing or chewing. If a dose is missed, the usual dose schedule should be followed without making up for the missed dose. These recommendations are not specific to MS and the drug should only be taken following doctor’s prescription and after discussing its risks and benefits.

Myrbetriq should not be taken if the patient has certain allergies, high blood pressure, kidney disease, liver disease, or bladder blockage (trouble urinating). The safety information is inadequate for use in children, and pregnant and breastfeeding women.

Doctor’s advice is needed to take other medications in combination with Myrbetriq. Several medications that are not recommended to take together with Myrbetriq include thioridazine, amphetamine, digoxin, flecainidine, metoprolol, desipramine, and warfarin.

Side effects of mirabegron include raised blood pressure, allergic reaction (itching, swelling, breathing troubles), painful urination, fever, constipation, irregular heartbeat, headache, back or side pain, dizziness, bladder pain, bloody or cloudy urine, and blurred vision.

Physician’s advice is needed for disposal of unused medication.