Safety and tolerability of the β3 -adrenoceptor agonist mirabegron, for the treatment of overactive bladder: results of a prospective pooled analysis of three 12-week randomised Phase III trials and of a 1-year randomised Phase III trial

Safety and tolerability of β3-adrenoceptor agonists in the treatment of overactive bladder syndrome - insight from transcriptosome and experimental studies

INTRODUCTION

We have reviewed the safety and tolerability of β3-adrenoceptor agonists, specifically mirabegron and solabegron, a newly emerging drug class for the treatment of the overactive bladder syndrome. We discuss them mechanistically in the context of expression and other preclinical data.

AREAS COVERED

Based on a systematic PubMed search, incidence of overall adverse events, hypertension, dry mouth, and constipation are comparable between mirabegron or solabegron and placebo. Hypertension is the most frequently observed adverse event, but has a similar incidence with mirabegron and placebo. Nevertheless, severe uncontrolled hypertension has become a contraindication for use of mirabegron based on observation of severe hypertension in association with mirabegron exposure. The overall incidence of adverse events is also similar between mirabegron and the muscarinic receptor antagonist tolterodine, but the incidence of dry mouth is much lower with mirabegron.

EXPERT OPINION

The high β3-adrenoceptor mRNA expression in the human ovaries is not associated with reproductive side effects. Generally, β3-adrenoceptors exhibit a rather restricted expression in human tissues, which may explain the overall good tolerability of agonists acting on this receptor. We propose that expression profiles and functional preclinical studies can be important tools in the prediction of adverse event profiles in first-in-class drugs.

[Pharmacotherapy of urinary incontinence in the elderly]

The prevalence and the incidence of Urinary Incontinence is growing. Women suffer predominantly from stress and mixed urinary incontinence and men from urge incontinence. In elderly people, the pathophysiological and the physiological change in the lower urinary tract system must be considered as well as an underlying multimorbidity. Stress urinary incontinence is among others caused by an insufficient urethral closure mechanism and urge incontinence is followed by unhibited detrusor contractions. Medical treatment is beside other important conservative options only one part of the treatment strategy in incontinence. Duloxetine, a serotonine-norepinephrine reuptake inhibitore can increase activity of the external urethral sphincter and is able to reduce incontinence episodes in up to 64 %. Antagonists of muscarinic receptors can reduce urgency, frequency and urge incontinence as well as increase bladder capacity significantly. In Germany, darifenacin, fesoterodin, oxybutynin, propiverine, solifenacin, tolterodine and trospium chloride are available to treat urge incontinence. The efficacy of these agents are almost comparable in the elderly with the exception of oxybutynin IR. However, tolerability is different and not well studied in the elderly population with the exception of fesoterodin. Side effects, especially dry mouth, dizziness and constipation often limit their use. None of the agents show ideal efficacy or tolerability in all patients. Last summer therefore a β3-agonist mirabegron was also introduced in Germany but was withdrawn.

Prospective Pilot Study of Mirabegron in Pediatric Patients with Overactive Bladder

BACKGROUND

Antimuscarinics are the pharmacologic mainstay of overactive bladder (OAB) management, but side effects limit their use. Mirabegron, a new molecule with a distinct mechanism of action (β3-adrenoreceptor agonist), was recently approved as monotherapy for idiopathic OAB in adults but has not been studied in the pediatric population.

OBJECTIVE

To evaluate the efficacy and safety of mirabegron to treat urinary incontinence in children with idiopathic OAB who were refractory to and/or intolerant of antimuscarinics.

DESIGN, SETTING, AND PARTICIPANTS

A prospective off-label study using mirabegron was conducted. Pediatric patients without symptom improvement under behavioral and medical therapies and/or with significant side effects with at least two different antimuscarinic agents were recruited.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Our primary outcome was better reported efficacy than with the use of prior anticholinergic medication. Secondary end points were tolerability, safety, and satisfaction. Efficacy and tolerability were assessed with voiding diaries, postvoid residuals, urine cultures, electrocardiogram, and vital signs. Families were questioned for continence, side effects, compliance, and Patient Perception of Bladder Condition (PPBC) questionnaire. The Wilcoxon rank sum test and Wilcoxon signed rank test were used for statistical analysis.

RESULTS AND LIMITATIONS

A total of 58 patients were recruited at a median age of 10.1 yr and were on mirabegron for a median of 11.5 mo. Median bladder capacity improved from 150ml to 200ml (p<0.001). Continence improved in 52 of 58, with 13 being completely dry. Median PPBC improved from 4.0 to 2.0 (p<0.001). Eight patients reported mild or moderate side effects. Absence of a placebo group is a limitation of the study.

CONCLUSIONS

Mirabegron, a novel first-in-class therapy, appeared as a safe and effective alternative for children with idiopathic OAB refractory to antimuscarinics.

PATIENT SUMMARY

We evaluated the efficacy and safety of mirabegron to treat incontinence in pediatric patients. Continence, median voided volumes, and quality of life were improved after the introduction of mirabegron, and few side effects were reported.

Involvement of β3-adrenoceptors in the inhibitory control of cholinergic activity in human bladder: Direct evidence by [(3)H]-acetylcholine release experiments in the isolated detrusor

Bladder overactivity (OAB) is a multifactorial bladder disorder that requires therapeutics superior to the current pharmacological treatment with muscarinic antagonists. β3-adrenoceptor (β3-ADR) agonists represent a novel promising approach that differently addresses the parasympathetic pathway, but the clinical efficacy of these drugs has not been fully elucidated to date. Therefore, we aimed to study the pharmacological mechanisms activated by β3-ADR agonists at muscular and neural sites in the isolated human bladder. Detrusor smooth muscle strips obtained from male patients undergoing total cystectomy were labelled with tritiated choline and stimulated with electrical field stimulation (EFS). EFS produced smooth muscle contraction and simultaneous acetylcholine ([(3)H]-ACh) release, which mostly reflects the neural origin of acetylcholine. Isoprenaline (INA), BRL37344 and mirabegron inhibited the EFS-evoked contraction and [(3)H]-ACh release in a concentration-dependent manner, yielding concentration-response curves (CRCs) that were shifted to the right by the selective β3-ADR antagonists L-748,337 and SR59230A. Based on the agonist potency estimates (pEC50) and apparent affinities (pKb) of antagonists evaluated from the CRCs of agonists, our data confirm the occurrence of β3-ADRs at muscle sites. Moreover, our data are consistent with the presence of inhibitory β3-ADRs that are functionally expressed at the neural site. Taken together, these findings elucidate the mechanisms activated by β3-ADR agonists because neural β3-ADRs participate in the inhibition of detrusor motor drive by reducing the amount of acetylcholine involved in the cholinergic pathway.