Myrbetriq (mirabegron) is a prescription medication used to treat overactive bladder (OAB) in adults. It offers an alternative approach for managing OAB symptoms.
Understanding Overactive Bladder
Overactive bladder (OAB) is a collection of symptoms that can significantly affect daily life. The condition is characterized by a sudden, compelling need to urinate, known as urinary urgency, which can be difficult to postpone. This urgency is often accompanied by increased urinary frequency, meaning urinating more often than usual. Additionally, urgency incontinence, the involuntary loss of urine associated with this sudden urge, can occur.
A healthy bladder typically functions by gradually filling with urine, expanding its capacity without involuntary contractions. As the bladder fills, nerves send signals to the brain, indicating it is time to urinate. This allows for controlled and voluntary emptying. In contrast, OAB disrupts this normal storage phase, causing the bladder muscle to contract unexpectedly before it is full, leading to the characteristic symptoms.
The Bladder’s Control System
The bladder’s function is intricately regulated by the autonomic nervous system. This system has two main branches: the sympathetic and parasympathetic nervous systems, which control the detrusor muscle, the smooth muscle forming the bladder wall. During the bladder’s filling phase, the sympathetic nervous system dominates, promoting urine storage by relaxing the detrusor muscle. This allows the bladder to expand and hold urine at low pressure.
Conversely, when it is time to urinate, the parasympathetic nervous system becomes active, stimulating the detrusor muscle to contract and push urine out. Located on the detrusor muscle are specific protein molecules called beta-3 adrenergic receptors (β3-ARs). When these beta-3 receptors are activated, they cause the detrusor muscle to relax. This relaxation is a key part of the bladder’s ability to store urine effectively.
How Myrbetriq Works
Myrbetriq (mirabegron) functions as a beta-3 adrenergic agonist. It selectively binds to and activates the beta-3 adrenergic receptors located on the detrusor muscle of the bladder. By stimulating these receptors, mirabegron promotes the relaxation of the detrusor muscle. This action is particularly relevant during the bladder’s filling or storage phase.
The activation of beta-3 receptors by mirabegron leads to an increase in cyclic adenosine monophosphate (cAMP) within the detrusor muscle cells. Elevated cAMP levels can inactivate an enzyme called myosin light chain kinase (MLCK), which is required for muscle contraction. This inactivation of MLCK contributes to the relaxation of the bladder muscle. This relaxation allows the bladder to hold a greater volume of urine without experiencing involuntary contractions. Unlike older medications that might block muscle contractions, mirabegron offers a different pathway by actively promoting relaxation, thereby increasing the bladder’s storage capacity.
Relieving OAB Symptoms
The relaxation of the detrusor muscle, facilitated by mirabegron’s action on beta-3 adrenergic receptors, reduces overactive bladder symptoms. By allowing the bladder to store more urine, Myrbetriq helps to decrease the sudden, compelling feeling of urgency. This increased bladder capacity also leads to a reduction in urinary frequency.
The improved bladder control helps to lessen episodes of urgency incontinence. The overall effect of Myrbetriq is to stabilize bladder function during the storage phase, thereby improving the quality of life for individuals with overactive bladder symptoms.