Vibegron
Vibegron, sold under the brand name Gemtesa, is a medication for the treatment of overactive bladder.Vibegron (other names: RVT-901; MK4618; KRP114V; URO-901) is a selective beta 3 adrenergic receptor agonist.
The most common side effects include headache, urinary tract infection, common cold, diarrhea, nausea, and upper respiratory tract infection.It was approved for medical use in the United States in December 2020.

Medical uses
Vibegron is indicated for the treatment of overactive bladder with symptoms of urge urinary incontinence, urgency, and urinary frequency in adults.

History and Discovery
The beta 3 adrenergic receptor was discovered in the late 1980s and initially beta3AR agonists were investigated as treatment for obesity and diabetes. A number of compounds were tested in clinical trials but didnt show sufficient benefits in these areas.Since the 2000s there is evidence that there are beta3AR on the detrusor muscle of the bladder. The detrusor muscle contracts during urination and remains relaxed to allow the bladder to store urine.
Mirabegron was the first FDA approved selective agonist approved to treat overactive bladder (OAB).Vibegron is a selective beta3AR agonist that is developed in Japan by Kyorin Pharmaceutical Co., Ltd and Kissei Pharmaceutical Co.,Ltd and Urovant Sciences to treat overactive bladders  and pain caused by irritable bowel syndrome. It was globally approved on September 21, 2018, in Japan for OAB.Vibegron has been proven effective in 5 key clinical trials.A phase IIb global trial completed in 2013 of 1395 patients, of which 89.7% were women and 63.3% had not been treated previously, demonstrated a significant decrease in daily micturitions and urgent urinary incontinence episodes upon administration of vibegron.An international phase III trial of 506 participants completed in 2019 found statistically significant efficacy of vibegron after 2 weeks of daily administration. The adverse effect rates in patients treated with vibegron were comparable to those in patients who received a placebo.GEMTESA, a drug using vibegron as an active ingredient was approved by the FDA on December 23, 2020, after an additional phase III international trial of 1085 patients.

Society and culture
Legal status
Vibegron was approved for medical use in the United States in December 2020.

Names
Vibegron is the international nonproprietary name (INN).

Mechanism of action
Vibegron is a selective agonist for the beta-3 adrenergic receptor (β3-AR). The receptors are located in the kidneys, urinary tract and bladder tissue. Upon binding, the β3 receptor undergoes a conformational change. This induces the activation of adenylate cyclases via G proteins and thereby promotes the formation of cyclic adenosine monophosphate (cAMP). The consequence of this cascade is an increased intracellular cAMP concentration which triggers activation of cAMP-dependent protein kinase A and causes a reduction of Ca2+ concentration in the cytoplasm. The kinase then phosphorylates myosin chains and thereby inhibits muscle contraction.The final effect of vibegron is muscle relaxation in the bladder. Due to this muscle relaxation, bladder capacity increases and symptoms of overactive bladder are relieved.

Metabolism
The two main metabolic pathways are the oxidation and glucuronidation of vibegron. Two oxidative metabolites and three glucuronide metabolites can be formed. The exact structure of these metabolites have not been studied yet. In vitro, CYP3A4 is the enzyme responsible for the metabolism of vibegron, facilitating oxidative metabolism. Eventually, still a large part of the unmodified drug is excreted through feces and urine.

Indications
Vibegron is indicated for people with OAB. Urgency urinary incontinence (UUI), urgency and urinary frequency in adults are the most common symptoms for this condition.The drug is contraindicated in patients with known hypersensitivity to Vibegron itself or single components of the drug. The inactive components of the drug for which allergic reactions can occur are sodium croscarmellose, hydroxypropyl cellulose, magnesium stearate, mannitol and microcrystalline cellulose. The thin coating of the drug with green color contains FD&C Blue No.2.Vibegron treatment should be discontinued if urinary retention occurs. Use with nonselective muscarinic antagonists may increase the risk of urinary retention. The manufacturer suggests discontinuing vibegron if an elevated digoxin concentration occurs.

Efficacy and side effects
Efficacy
Vibegron was evaluated in patients with overactive bladder (OAB) in several clinical studies. A large active-controlled study, called Empower, showed the beneficial effects of the drug to treat the condition and UUI. Primary outcomes of different clinical trials showed there was an overall increase in efficacy. These outcomes concluded that there was a reduction in urgency to urinate, a decrease in micturitions and a decrease in average volume voided per micturition. There is also an improvement observed of the symptoms when Vibegron is administered over a longer period (52 weeks) concluding that it is effective and safe for longer use. In severe patients, increasing the dose was accompanied by similar beneficial effects when there was first a lack of these. Quality of life of the patients is improved, including a reduction of nocturia.

Adverse effects
The most common side effects of Vibegron are a dry mouth, constipation, headache, nasopharyngitis, diarrhea, nausea, bronchitis, urinary tract infection and upper respiratory tract infection. An indication is made that upon urinary retention development, the patient should stop using the drug. Risk assessment for the drug in pregnant women has yet to be evaluated.

Interactions
Vibegron is in contrast to other OAB drugs very selective and leads to a lesser degree in unwanted side effects. Vibegron is found to be a substrate for CYP3A4 in vivo, but does not actually induce or inhibit any of the cytochrome P450 enzymes and is thus less likely to take part in drug–drug interactions (DDI). Here vibegron differs from the previous overactive bladder drug mirabegron, which was known to be associated in various drug–drug interactions by inhibiting CYP2D6 or inducing CYP3A4, CYP2D6 and CYP2C9 in the liver.Using Vibegron only (monotherapy) has positive effects on OAB and UUI, but a combination with other drugs can have additional effects. In a study with antimuscarinic drugs, more DDIs were investigated using a model of Rhesus monkeys. Dose combinations of vibegron and tolterodine showed increased bladder capacity, the effects of both drugs at low dosis strengthened each other, known as synergism. The addition of darifenacin to vibegron created greater bladder relaxation only when used at high doses. Additionally, co-administration with Imidafenacin shows an increase in bladder capacity and voided volume in comparison to monotherapy. Possibly, a widely adapted treatment will be the combination of beta-3-adrenergic agonist with a nonselective M2/M3 antagonist as the most prevalent option.Clinical studies show no significant drug–drug interaction (DDI), aside from a serum concentration increase of digoxin when taken with vibegron. Maximal concentrations and systemic exposure (Cmax and area under the curve (AUC)) of digoxin are both increased as a result of DDI.  Apart from the no to little DDIs, Vibegron has an additional safety quality in that it does not cross the blood-brain barrier and therefore does not induce cognitive impairment. Furthermore, Vibegron can be taken with or without food, this does not have an effect on vibegron plasma concentrations.

Toxicity
Effects on animals
Pregnant rats were given very high daily oral doses of Vibegron during the period of organogenesis and showed no embryo-fetal developmental toxicity up to 300 mg/kg/day. Similar data was found in rabbits. Maternal toxicity was observed when doses exceeded 100 mg/kg/day in lactating rats. Clinical studies show that Vibegron is not toxic, safe and well-tolerated in patients.

References
External links
"Vibegron". Drug Information Portal. U.S. National Library of Medicine.
Clinical trial number NCT03492281 for "A Study to Examine the Safety and Efficacy of a New Drug in Patients With Symptoms of Overactive Bladder (OAB) (Empowur)" at ClinicalTrials.gov