Beta 3 agonists are a class of medications that interact with beta-3 adrenergic receptors in the body. These receptors are a type of protein found on the surface of various cells, acting like receiving stations for chemical signals. When a beta 3 agonist binds to these receptors, it triggers a specific cellular response. This interaction is selective, primarily targeting beta-3 receptors rather than other related receptors like beta-1 or beta-2, which have distinct functions elsewhere in the body. Beta 3 agonists are a newer class of medications with growing therapeutic applications.
How Beta 3 Agonists Function
Beta-3 adrenergic receptors are found in various body areas, notably in fat cells and the detrusor muscle of the urinary bladder. When a beta 3 agonist binds to these receptors, it initiates intracellular events. This binding activates a Gs protein, stimulating adenylyl cyclase. This enzyme converts adenosine triphosphate (ATP) into cyclic adenosine monophosphate (cAMP), a secondary messenger within the cell.
Elevated cAMP levels then activate protein kinase A (PKA), which phosphorylates target proteins. In the bladder, this cascade leads to detrusor smooth muscle relaxation. This relaxation allows the bladder to hold more urine during the filling phase. The mechanism may also involve inhibiting acetylcholine release from bladder nerves, further contributing to muscle relaxation and reduced bladder activity.
Treating Overactive Bladder
Overactive bladder (OAB) is a common condition marked by a sudden, strong urge to urinate that is difficult to defer. This urgency often includes frequent urination, day and night, and sometimes urge incontinence, which is involuntary urine leakage. These symptoms result from involuntary contractions of the detrusor muscle, even when the bladder is not full.
Beta 3 agonists manage OAB symptoms by directly addressing bladder muscle activity. By stimulating beta-3 adrenergic receptors on the detrusor muscle, these medications promote muscle relaxation during the bladder’s storage phase. This relaxation increases the bladder’s capacity, reducing urgency and urination frequency. It also helps prevent sudden, uncontrolled contractions that cause urge incontinence.
Clinical trials show beta 3 agonists effectively reduce daily urination, urgency, and incontinence episodes in OAB patients. This mechanism offers an advantage over older OAB medications like antimuscarinics, which block different receptors and have different side effects. Beta 3 agonists enhance bladder storage, making them a valuable option for improving quality of life for those with OAB.
Key Medications
Several prescription beta 3 agonists are available for treating overactive bladder. Mirabegron, sold as Myrbetriq and Betmiga, was the first in this class approved in the United States and Europe for OAB treatment.
Another medication is vibegron, available as Gemtesa. Both mirabegron and vibegron are administered as oral tablets. Other beta 3 agonists, such as solabegron, have been in clinical trials for OAB and other conditions.
Important Considerations and Side Effects
While generally well-tolerated, beta 3 agonists can cause side effects, and certain considerations are important for their use. Common side effects include headache, constipation, urinary tract infections, and dizziness. Some individuals may also experience increased blood pressure, particularly those with pre-existing hypertension. Nasopharyngitis, which is inflammation of the nose and throat, is another reported side effect.
Healthcare providers exercise caution when prescribing beta 3 agonists to patients with severe uncontrolled hypertension due to the potential for elevated blood pressure. While these medications generally have a favorable safety profile compared to some older OAB treatments, it is important to discuss any existing medical conditions and all other medications being taken with a healthcare professional. Consulting a doctor is also necessary if side effects become bothersome or if there are concerns about the medication’s effectiveness.