Identification of human cytochrome P450 isoforms and esterases involved in the metabolism of mirabegron, a potent and selective β3-adrenoceptor agonist

Pre-Steady-State and Steady-State Kinetic Analysis of Butyrylcholinesterase-Catalyzed Hydrolysis of Mirabegron, an Arylacylamide Drug

The β-adrenergic drug Mirabegron, a drug initially used for the treatment of an overactive bladder, has new potential indications and is hydrolyzed by butyrylcholinesterase (BChE). This compound is one of the only arylacylamide substrates to be catabolized by BChE. A steady-state kinetic analysis at 25 °C and pH 7.0 showed that the enzyme behavior is Michaelian with this substrate and displays a long pre-steady-state phase characterized by a burst. The induction time, τ, increased with substrate concentration (τ ≈ 18 min at maximum velocity). The kinetic behavior was interpreted in terms of hysteretic behavior, resulting from a slow equilibrium between two enzyme active forms, E and E'. The pre-steady-state phase with the highest activity corresponds to action of the E form, and the steady state corresponds to action of the E' form. The catalytic parameters were determined as kcat = 7.3 min-1 and Km = 23.5 μM for the initial (burst) form E, and kcat = 1.6 min-1 and Km = 3.9 μM for the final form E'. Thus, the higher affinity of E' for Mirabegron triggers the slow enzyme state equilibrium toward a slow steady state. Despite the complexity of the reaction mechanism of Mirabegron with BChE, slow BChE-catalyzed degradation of Mirabegron in blood should have no impact on the pharmacological activities of this drug.

Drug and pro-drug substrates and pseudo-substrates of human butyrylcholinesterase

Butyrylcholinesterase (BChE) is present in plasma and numerous cells and organs. Its physiological function(s) is(are) still unclear. However, this enzyme is of pharmacological and toxicological importance. It displays a broad specificity and is capable of hydrolyzing a wide range of substrates with turnovers differing by several orders of magnitude. Nowaday, these substrates include more than two dozen carboxyl-ester drugs, numerous acetylated prodrugs, and transition state analogues of acetylcholine. In addition, BChE displays a promiscuous hydrolytic activity toward amide bonds of arylacylamides, and slowly hydrolyzes carbamyl- and phosphoryl-esters. Certain pseudo-substrates like carbamates and organophosphates are major drugs of potential medical interest. The existence of a large genetic poly-allelism, affecting the catalytic properties of BChE is at the origin of clinical complications in the use of certain drugs catabolized by BChE. The number of drugs and prodrugs hydrolyzed by BChE is expected to increase in the future. However, very few quantitative data (Km, kcat) are available for most marketed drugs, and except for myorelaxants like succinylcholine and mivacurium, the impact of BChE genetic mutations on catalytic parameters has not been evaluated for most of these drugs.

Possible Involvement of Muscarinic Receptor Blockade in Mirabegron Therapy for Patients with Overactive Bladder

The selective β ₃-adrenoceptor agonist mirabegron, an established alternative to antimuscarinic therapy for patients with overactive bladder, induces additional effects against receptors, transporters, and hepatic enzymes. The present study aimed to elucidate the effects of mirabegron on muscarinic receptors in the rat bladder using radioligand binding and functional assays. Mirabegron (0.1-100 μM) inhibited specific [N-methyl-³H]scopolamine methyl chloride binding in the bladder and other tissues of rats in a concentration-dependent manner. Binding affinity in the bladder was similar to that in the heart and significantly higher than those in the submaxillary gland and brain. Mirabegron induced the concentration-dependent relaxation of carbachol-induced contractions in the rat isolated bladder. Further analyses using a two-site model revealed that the relative quantities of high- and low-affinity components for mirabegron were 44.5% and 55.5%, respectively. Respective pEC₅₀ values were 7.06 and 4.97. Based on the receptor binding affinity and pharmacokinetics of mirabegron, muscarinic receptor occupancy in the human bladder for 24 hours after the administration of a single oral dose of 50 mg mirabegron was 37%-76%. The present results demonstrate for the first time that mirabegron may relax the detrusor smooth muscle not only by β ₃-adrenoceptor activation but also muscarinic receptor blockade. SIGNIFICANCE STATEMENT: Mirabegron, the first selective β ₃-adrenoceptor agonist, represents an alternative to antimuscarinic agents for management of overactive bladder (OAB). The present study aimed to clarify whether mirabegron directly binds to muscarinic receptors and affects cholinergic agonist-induced contractions in rat urinary bladder and to predict muscarinic receptor occupancy in human bladder after oral administration of mirabegron. The results demonstrated that mirabegron therapy for patients with OAB may be due not only to β ₃-adrenoceptor activation but also muscarinic receptor blockade.

Potential of Mirabegron and its Extended-release Formulations for the Treatment of Overactive Bladder Syndrome

BACKGROUND

Overactive bladder syndrome is a broadly occurring urological disorder with a distressing impact on the quality of life. The commonly used antimuscarinic drugs show poor patient compliance because of unsatisfactory potency, tolerability and high occurrence of adverse effects such as dry mouth, blurred vision, constipation, dizziness etc. Mirabegron is the first approved β3-adrenoreceptor agonist, used as mono or in combination therapies for overactive bladder syndrome.

OBJECTIVE

The present review provides an insight into the mechanism, pharmacokinetics, toxicokinetics, clinical trials and the development of various conventional and modified-release dosage forms of mirabegron for the treatment of overactive bladder syndrome.

RESULTS

The clinical trials of phase II and phase III of mirabegron demonstrated symptomatic relief from the overactive bladder without disturbing the micturition cycle. To date, mirabegron showed promising results for safety, tolerability and efficacy in patients with overactive bladder syndrome. The modified-release tablet dosage form of mirabegron appear to be a proficient and suitable replacement for antimuscarinics and revealed the tremendous potential to overcome the adverse effects of conventional antimuscarinic drugs like Oxybutyline chloride ER, Detrol LA, VESIcare, etc. Conclusion: Mirabegron shows a distinct mode of action, i.e., targeting β3-adrenoreceptors and improving bladder storage without altering void contractions. The limited side effects, high safety, efficacy and tolerability of mirabegron present an adequate substitute to antimuscarinics. However, long-term analysis and clinical studies are prerequisites for assessing the safety, tolerability and efficacy profile of mirabegron.

Physiologically Based Pharmacokinetic Modeling Suggests Limited Drug-Drug Interaction for Fesoterodine When Coadministered With Mirabegron

5-Hydroxymethyl tolterodine (5-HMT; the active fesoterodine metabolite) is metabolized via the cytochrome P450 (CYP) 2D6 and CYP3A pathways. Mirabegron is a moderate CYP2D6 inhibitor and weak CYP3A inhibitor. Potential drug-drug interactions (DDIs) following coadministration of these 2 overactive bladder treatments were estimated using physiologically based pharmacokinetic models, developed and verified by comparing predicted and observed pharmacokinetic profiles from clinical studies. Models predicted and verified mirabegron and desipramine (CYP2D6 substrate) and 5-HMT and ketoconazole (strong CYP3A inhibitor) DDIs. Mirabegron model-predicted mean steady-state AUC and C_max were within 11% of clinical observations. The predicted versus observed geometric mean ratio (GMR) of AUC_inf for CYP2D6 substrates desipramine and metoprolol coadministered with mirabegron 100 or 160 mg once daily were 3.47 versus 3.41 and 2.97 versus 3.29, respectively, indicating that the mirabegron model can be used to predict clinical CYP2D6 inhibition. 5-HMT fractional clearance by CYP3A and CYP2D6 was verified from clinical DDI studies with a potent CYP3A4 inhibitor (ketoconazole) and inducer (rifampicin) in CYP2D6 extensive and poor metabolizers and with a moderate CYP3A inhibitor (fluconazole) in healthy volunteers. 5-HMT AUC_inf and C_max GMRs for fesoterodine DDIs were all predicted within 1.26-fold of clinical observation, providing verification for the fesoterodine substrate model. The predicted changes in 5-HMT AUC_inf and C_max ratios for 8 mg fesoterodine when coadministered with 50 mg mirabegron were 1.22-fold and 1.17-fold, respectively, relative to 8 mg fesoterodine given alone. This modest increase in 5-HMT exposures by approximately 20% is considered clinically insignificant and would not require fesoterodine dose adjustment when coadministered with mirabegron within approved daily-dose ranges.

Determination of Mirabegron in rat plasma by UPLC-MS/MS after oral and intravenous administration

Mirabegron is a kind of β3 adrenergic receptor agonist which is an effective drug for the treatment of overactive bladder. In this research, a UPLC-MS/MS method is developed and validated for the study of mirabegron pharmacokinetic in rats. A protein precipitation method is applied for sample preparation with acetonitrile. m/z 397.3→379.6, m/z 326.4→121.0 for mirabegron, tolterodine (IS), respectively in the positive ion mode was performed for quantitation. The method is reliable and reproducible in our study (intra-day precision≤11.06%, inter-day precision≤11.43%) with concentration curves linear from 5 to 2500 ng/mL(R2>0.999). Stability studies demonstrated that mirabegron was stable under a variety of storage conditions. This method was successfully applied for determining mirabegron in rats after oral and intravenous administration.

Physiologically-based pharmacokinetic modeling for mirabegron: a multi-elimination pathway mediated by cytochrome P450 3A4, uridine 5'-diphosphate-glucuronosyltransferase 2B7, and butyrylcholinesterase

This was the first study to construct a physiologically-based pharmacokinetic (PBPK) model for mirabegron which incorporates the overall elimination pathways of metabolism by cytochrome P450 (CYP) 3A4, uridine 5'-diphosphate-glucuronosyltransferase (UGT) 2B7, and butyrylcholinesterase (BChE) and renal excretion. The objective was to assess the risk of drug-drug interactions (DDIs) by estimating the contribution of each elimination pathway and simulating the magnitude of the DDIs with UGT2B7 inhibitors. A PBPK model for mirabegron was constructed to reproduce the plasma concentration-time curves from a phase 1 study and the magnitude of the DDI with ketoconazole taking into account the overall elimination pathways. The PBPK model was subsequently verified using data from other DDI studies. The constructed PBPK model estimated the contribution for each elimination pathway: 44% and 29% for CYP3A4 and UGT2B7 in the liver, 1.6% for UGT2B7 in the kidney, 3.2% for BChE in plasma, and 22% for renal excretion. Co-administration of probenecid (an UGT2B7 inhibitor) or fluconazole (an UGT2B7 and CYP3A4 inhibitor) was predicted to increase area under the curve for mirabegron to 115% or 174%, respectively. In conclusion, PBPK modeling and simulation revealed a low DDI risk for mirabegron following co-administration with BChE or UGT2B7 inhibitors.

Mirabegron: potential off target effects and uses beyond the bladder

The β₃ -adrenoceptor was initially an attractive target for several pharmaceutical companies due to its high expression in rodent adipose tissue, where its activation resulted in decreased adiposity and improved metabolic outputs (such as glucose handling) in animal models of obesity and Type 2 diabetes. However, several drugs acting at the β₃ -adrenoceptor failed in clinical trials. This was thought to be due to their lack of efficacy at the human receptor. Recently, mirabegron, a β₃ -adrenoceptor agonist with human efficacy, was approved in North America, Europe, Japan and Australia for the treatment of overactive bladder syndrome. There are indications that mirabegron may act at other receptors/targets, but whether they have any clinical relevance is relatively unknown. Besides overactive bladder syndrome, mirabegron may have other uses such as in the treatment of heart failure or metabolic disease. This review gives an overview of the off-target effects of mirabegron and its potential use in the treatment of other diseases.

LINKED ARTICLES

This article is part of a themed section on Molecular Pharmacology of GPCRs. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.21/issuetoc.

Sirolimus and mirabegron interaction in a hematopoietic cell transplant patient

PURPOSE

Hematopoietic cell transplant patients are exposed to numerous classes of medications. Transplant practitioners must vigilantly monitor for drug interactions especially involving immunosuppressants. We report a hematopoietic cell transplant patient receiving sirolimus who developed supratherapeutic serum concentrations after initiating mirabegron.

SUMMARY

A 31-year-old, 98 kg female received a second umbilical cord blood transplant four years after the first transplant for relapsed acute myeloid leukemia. Mycophenolate mofetil and sirolimus were utilized for graft versus host disease prophylaxis. The patient was receiving sirolimus 2 mg daily and the serum concentration on day 26 post-transplant (day + 26) was within therapeutic range (6.7 μg/L, goal range 3-12 μg/L). Her post-transplant course was complicated by BK viruria-associated cystitis for which she was started on mirabegron. Six days after starting the new medication (day + 33), the sirolimus serum concentration increased to 19.2 μg/L. Thus mirabegron was discontinued and sirolimus was held. Sirolimus was restarted once the serum concentration was within goal and subsequently stabilized with a combination of 1 mg and 2 mg daily for a total weekly dose of 10 mg. The proposed mechanisms of interaction include: (1) sirolimus inhibition of organic anion transporting polypeptide leading to increased mirabegron in the intestinal lumen; (2) mirabegron inhibition of P-glycoprotein leading to increased absorption of sirolimus and; (3) increased sirolimus absorption leading to increased sirolimus serum concentrations.

CONCLUSION

To our knowledge, this is the first report of a potential drug interaction between sirolimus and mirabegron. Transplant specialists should be aware of this potential interaction when considering the concurrent use of these medications.

Pharmacokinetic drug interaction study between overactive bladder drugs mirabegron and tolterodine in Japanese healthy postmenopausal females

Mirabegron, the first selective β₃-adrenoceptor agonist for the treatment of overactive bladder (OAB), inhibits cytochrome P450 isozyme CYP2D6. This study was performed in Japanese healthy postmenopausal female volunteers to assess any pharmacokinetic drug interaction between mirabegron and tolterodine, another OAB drug and a sensitive substrate of CYP2D6. Tolterodine 4 mg was orally administered from Days 1-7 and co-administered with mirabegron 50 mg from Days 8-14. Mirabegron 50 mg increased maximum concentration (C_max) and area under the concentration-time curve from zero to 24 h after dosing (AUC_24h) of tolterodine by 2.06-fold (90% confidence interval [CI] 1.81, 2.34) and 1.86-fold (90% CI 1.60, 2.16), respectively, and increased C_max and AUC_24h of the metabolite 5-hydroxymethyl tolterodine by 1.36-fold (90% CI 1.26, 1.47) and 1.25-fold (90% CI 1.15, 1.37), respectively. This suggested a weak pharmacokinetic drug interaction between mirabegron and tolterodine. Mean change from baseline of Fridericia's QT correction formula (ΔQTcF) was slightly higher on Day 14 than on Day 7. No subject had QTcF >480 msec or ΔQTcF >60 msec. All the treatment-emergent adverse events were mild. Mirabegron 50 mg was considered to be safe and well tolerated when coadministered with tolterodine 4 mg in healthy postmenopausal female volunteers.

Metabolism elucidation of BJ-B11 (a heat shock protein 90 inhibitor) by human liver microsomes: identification of main contributing enzymes

OBJECTIVE

The aim of this article is to elucidate the metabolic pathways of BJ-B11, a heat shock protein 90 inhibitor, in human liver microsomes (HLM) and determine the main enzymes responsible for formation of each metabolite.

METHODS

Metabolites of BJ-B11 were identified using the ultra performance liquid chromatography- quadrupole time-of-flight/mass spectrometry (UPLC-QTOF/MS) method. Esterase contributing to the hydrolysis of BJ-B11 was identified by chemical inhibition and activity correlation assays. Reaction phenotyping and kinetic studies using expressed cytochrome P450 (CYP) enzymes were performed to determine the contributions of CYP isozymes to BJ-B11 metabolism.

RESULTS

BJ-B11 was rapidly hydrolyzed to generate a deacetylated product M1-1. M1-1 was subsequently metabolized to form eight metabolites. Hydrolysis of BJ-B11 was markedly inhibited by vinblastine (a dual inhibitor of arylacetamide deacetylase and carboxylesterase 2). By contrast, digitonin and telmisartan (the specific inhibitors for carboxylesterase 1 and carboxylesterase 2, respectively) did not inhibit BJ-B11 hydrolysis at all. Further, BJ-B11 hydrolysis was significantly correlated with hydrolysis of phenacetin (an activity marker of arylacetamide deacetylase). Moreover, reaction phenotyping revealed that metabolism of M1-1 in HLM was attributable to several CYP enzymes, including CYP1A1, 1B1, 3A4 and 3A5.

CONCLUSION

BJ-B11 was subjected to efficient metabolism in the liver, generating nine metabolites. BJ-B11 metabolism was contributed mainly by arylacetamide deacetylase and multiple CYP enzymes.

β3-Adrenoceptor agonists for overactive bladder syndrome: Role of translational pharmacology in a repositioning clinical drug development project

β3-Adrenoceptor agonists were originally considered as a promising drug class for the treatment of obesity and/or type 2 diabetes. When these development efforts failed, they were repositioned for the treatment of the overactive bladder syndrome. Based on the example of the β3-adrenoceptor agonist mirabegron, but also taking into consideration evidence obtained with ritobegron and solabegron, we discuss challenges facing a translational pharmacology program accompanying clinical drug development for a first-in-class molecule. Challenges included generic ones such as ligand selectivity, species differences and drug target gene polymorphisms. Challenges that are more specific included changing concepts of the underlying pathophysiology of the target condition while clinical development was under way; moreover, a paucity of public domain tools for the study of the drug target and aspects of receptor agonists as drugs had to be addressed. Nonetheless, a successful first-in-class launch was accomplished. Looking back at this translational pharmacology program, we conclude that a specifically tailored and highly flexible approach is required. However, several of the lessons learned may also be applicable to translational pharmacology programs in other indications.

A highly selective marker reaction for measuring the activity of human carboxylesterase 1 in complex biological samples

NMHN hydrolysis was found to be a highly selective marker reaction for sensing the activity of human carboxylesterase 1 (hCE1).

Liquid Chromatographic Separation and Thermodynamic Investigation of Mirabegron Enantiomers on a Chiralpak AY-H Column

Liquid chromatographic separation of mirabegron enantiomers on Chiralpak AY-H, a column coated with amylose tris-(5-chloro-2-methylphenylcarbamate) as a chiral stationary phase, was studied under normal phase conditions. The influence of ethanol content (30-45%) and column temperature (20-40°C) on retention, resolution and separation were evaluated. Apparent thermodynamic parameters deduced from Van't Hoff plots were used to understand chiral separation mechanisms, and the chiral separation was enthalpy driven. The optimized chromatographic conditions were using a mixture solution of n-hexane, ethanol and diethyl amine (55 : 45 : 0.1, v/v/v) as a mobile phase at a flow rate of 1.0 mL/min. The column temperature and UV detector were set at 35°C and 254 nm, respectively. The method was validated to be simple, accuracy, sensitive and robust according to the ICH guidelines, and it was suitable for the routine quality control of mirabegron enantiomers for pharmaceutical industries.

Pharmacokinetics of mirabegron, a β3-adrenoceptor agonist for treatment of overactive bladder, in healthy Japanese male subjects: results from single- and multiple-dose studies

BACKGROUND

Mirabegron is a human β3-adrenoceptor agonist for the treatment of overactive bladder. The pharmacokinetic profile of mirabegron has been extensively characterized in healthy Caucasian subjects.

OBJECTIVE

The objective of this study was to evaluate the pharmacokinetics, dose-proportionality, and tolerability of mirabegron following single and multiple oral doses in healthy Japanese male subjects. The results were compared with those reported in non-Japanese (primarily Caucasian) subjects.

METHODS

Two studies were conducted. In a single-blind, randomized, placebo-controlled, parallel-group, single- and multiple-ascending dose study (Study 1), mirabegron oral controlled absorption system (OCAS) tablets were administered at single doses of 50, 100, 200, 300, and 400 mg, with eight subjects (six active, two placebo) per dose group (Part I), and once daily for 7 days at 100 and 200 mg with 12 subjects (eight active, four placebo) per group (Part II). In an open-label, three-period, single-ascending dose study (Study 2), mirabegron OCAS was administered to 12 subjects at 25, 50, and 100 mg in an intra-subject dose-escalation design. Plasma and/or urine samples were collected up to 72 h after the first and last dose and analyzed for mirabegron. Pharmacokinetic parameters were determined using non-compartmental methods. Tolerability assessments included physical examinations, vital signs, 12-lead electrocardiogram, clinical laboratory tests (biochemistry, hematology, and urinalysis), and adverse event (AE) monitoring.

RESULTS

Forty and 24 young male subjects completed Part I and II, respectively, of Study 1. Twelve young males completed Study 2. After single oral doses (25-400 mg), maximum plasma concentrations (C max) were reached at approximately 2.8-4.0 h postdose. Plasma exposure (C max and area under the plasma concentration-time curve) of mirabegron increased more than dose proportionally at single doses of 25-100 mg and approximately dose proportionally at high doses of 300 and 400 mg. A more than dose proportional increase in plasma exposure was noted in the body of the same individual. Mirabegron accumulated twofold upon once-daily dosing relative to single-dose data. Steady state was reached within 7 days. Mirabegron was generally well-tolerated at single doses up to 400 mg and multiple doses up to 200 mg. The AE with the highest incidence was increased pulse rate at 400 mg in Study 1.

CONCLUSIONS

Mirabegron OCAS exhibits similar single- and multiple-dose pharmacokinetic characteristics and deviations from dose proportionality in healthy Japanese male subjects compared with those observed in non-Japanese (primarily Caucasian) subjects in previous studies.

Mirabegron in the treatment of overactive bladder

INTRODUCTION

Mirabegron is a selective β3-adrenergic receptor agonist recently developed for the treatment of patients with overactive bladder (OAB), which offers an alternative pharmacological option to the well-established treatment with antimuscarinics (AMs).

AREAS COVERED

This review offers an explanation of the mechanism of action, of the pharmacokinetics and pharmacodynamics of mirabegron and gives readers a complete overview of Phase II and III studies on the clinical efficacy, tolerability and safety of this agent in the setting of OAB treatment.

EXPERT OPINION

Both Phase II and III trials have shown that mirabegron is efficacious and safe in treating patients with OAB. Future research should focus on the assessment of mirabegron concentrations in the CNS and on the evaluation of the potential of the combination of mirabegron with AMs. Another field for future research is represented by the investigation of the interaction of mirabegron with CYP2D6 inhibitors. Furthermore, current literature completely lacks studies on the efficacy and safety of mirabegron in the pediatric population and such trials are awaited.

Discovery history and clinical development of mirabegron for the treatment of overactive bladder and urinary incontinence

INTRODUCTION

Overactive bladder (OAB) and urinary incontinence, although not life-threatening, are very bothersome chronic health conditions. The limitations of current pharmacological treatment urge the need for novel drugs with alternative mechanisms of action. Huge efforts in this area of research led to the synthesis of several selective and potent β3-adrenoceptor agonists that gained relevance through research during the late 80s and 90s. Mirabegron was the first compound of this new class of drugs that showed preclinical efficacy in several models of storage bladder dysfunction, together with a favorable human pharmacological profile. Having passed the proof-of-concept stage, an extensive clinical development and pharmacology program was performed during the last 10 years, involving >10,000 individuals, before mirabegron was granted marketing approval.

AREAS COVERED

In this case history, the authors review the milestones in mirabegron's discovery based on a systematic literature review.

EXPERT OPINION

Thanks to its tolerability and safety/efficacy balance, mirabegron has potential to fill a need for new treatment options for OAB, and paves the way for further development of a completely new class of drugs aimed to treat this condition. However, the exact role of mirabegron in clinical practice has yet to be defined. Further studies are needed in order to clarify, together with post-launch information, critical safety issues and cost-effectiveness in head-to-head comparison with current standard treatments.

Impact of mirabegron extended-release on the treatment of overactive bladder with urge urinary incontinence, urgency, and frequency

Overactive bladder is a highly prevalent disorder with a significant impact on quality of life. Antimuscarinic agents are commonly used, but persistence is limited due to unsatisfactory efficacy and/or tolerability. Mirabegron is the first beta-3 adrenoceptor agonist approved for the treatment of overactive bladder syndrome. This paper reviews the pharmacology, mechanism of action, efficacy, and safety of mirabegron. A PubMed search of all English articles pertaining to mirabegron was performed. An alternative to antimuscarinics, mirabegron has a unique mechanism, improves overactive bladder symptoms and quality of life, and has limited adverse effects and few contraindications.

Mirabegron in overactive bladder: a review of efficacy, safety, and tolerability

AIMS

Mirabegron, the first β3 -adrenoceptor agonist to enter clinical practice, has a different mechanism of action from antimuscarinic agents. This review presents data on the efficacy, safety, and tolerability of mirabegron in studies conducted to date.

METHODS

All clinical data on mirabegron that are currently in the public domain are included, including some in-press manuscripts.

RESULTS

In Phase III clinical trials in patients with overactive bladder (OAB), mirabegron at daily doses of 25, 50, and 100 mg demonstrated significant efficacy in treating the symptoms of OAB, including micturition frequency, urgency incontinence, and urgency. Significant improvements in micturition frequency, urgency incontinence, and mean volume voided/micturition were seen as early as the first assessment (week 4) for mirabegron 50 and 100 mg, and were maintained throughout treatment. Responder analyses showed a significant improvement with mirabegron 50 and 100 mg in terms of dry rates, ≥50% reduction in mean number of incontinence episodes/24 hr, and the proportion of patients with ≤8 micturitions/24 hr at final visit. The benefit of mirabegron 50 and 100 mg was also evident in patients ≥65 years of age, and in both treatment-naïve patients and those who previously discontinued antimuscarinic therapy. These data therefore demonstrate a clinically meaningful benefit with mirabegron in the objective endpoints of OAB. Assessment of measures of health-related quality of life and treatment satisfaction showed that patients perceived treatment with mirabegron as meaningful. In OAB clinical trials of up to 12 months mirabegron appeared to be well tolerated. The most common adverse events (AEs) observed with mirabegron in clinical trials of up to 12 months were hypertension, nasopharyngitis, and urinary tract infection. The incidence of dry mouth was similar to placebo, and was between three and fivefold less than for tolterodine extended release 4 mg. Since dry mouth is the most bothersome AE associated with antimuscarinic drugs and often a reason for treatment discontinuation, mirabegron may be a valuable treatment option for these patients.

CONCLUSIONS

In Phase III clinical trials, mirabegron at daily doses of 25, 50, and 100 mg demonstrated significant efficacy in treating symptoms of OAB and, at doses of 50 and 100 mg, demonstrated significant improvements versus placebo on key secondary endpoints, as early as the first assessment (week 4), and these were maintained throughout treatment. In OAB clinical trials of up to 12 months, mirabegron appeared to be well tolerated.

The effect of mirabegron, a potent and selective β3-adrenoceptor agonist, on the pharmacokinetics of CYP2D6 substrates desipramine and metoprolol

Mirabegron is a potent and selective β3-adrenoceptor agonist developed for the treatment of overactive bladder. In vitro studies demonstrated that mirabegron partly acts as a (quasi-) irreversible, metabolism-dependent inhibitor of CYP2D6. The effect of steady-state mirabegron on single doses of the sensitive CYP2D6 substrates metoprolol (100 mg) and desipramine (50 mg) was assessed in two open-label, one-sequence crossover studies in healthy subjects (CYP2D6 extensive metabolizers). Mirabegron 160 mg/day increased metoprolol maximum plasma concentration (C max) 1.90-fold (90 % confidence interval [CI] 1.54; 2.33) and total exposure (AUC0-∞) 3.29-fold (90 % CI 2.70; 4.00) in 12 males (study 1). Mean metoprolol half-life increased from 2.96 to 4.11 h. α-Hydroxymetoprolol C max and AUC to last measurable concentration decreased 2.6-fold and 2.2-fold, respectively. In study 2, mirabegron 100 mg/day increased desipramine C max 1.79-fold (90 % CI 1.69; 1.90) and AUC0-∞ 3.41-fold (90 % CI 3.07; 3.80) in 14 males and 14 females. Mean desipramine half-life increased from 19.5 to 35.8 h. C max of 2-hydroxydesipramine decreased ~twofold, while AUC increased ~1.3-fold. Desipramine was administered again 2 weeks after the last mirabegron dose. Desipramine C max and AUC0-∞ were still ~1.13-fold increased; the 90 % CIs fell within the 0.80-1.25 interval. All treatments were well tolerated. In conclusion, mirabegron is a moderate CYP2D6 inhibitor (ratio and 90 % CI <5.0).

Intestinal absorption mechanism of mirabegron, a potent and selective β₃-adrenoceptor agonist: involvement of human efflux and/or influx transport systems

Mirabegron, a weak-basic compound, is a potent and selective β3-adrenoceptor agonist for the treatment of overactive bladder. Mirabegron extended release formulation shows dose-dependent oral bioavailability in humans, which is likely attributable to saturation of intestinal efflux abilities leading to higher absorption with higher doses. This study evaluated the membrane permeability of mirabegron and investigated the involvement of human intestinal transport proteins in the membrane permeation of mirabegron. Transcellular transport and cellular/vesicular uptake assays were performed using Caco-2 cells and/or human intestinal efflux (P-glycoprotein [P-gp], breast cancer resistance protein [BCRP], and multidrug resistance associated protein 2 [MRP2]) and influx (peptide transporter 1 [PEPT1], OATP1A2, and OATP2B1) transporter-expressing cells, vesicles, or Xenopus laevis oocytes. The absorptive permeability coefficients of mirabegron in Caco-2 cells (1.68-1.83 × 10(-6) cm/s) at the apical and basal pH of 6.5 and 7.4, respectively, were slightly higher than those of nadolol (0.97-1.41 × 10(-6) cm/s), a low permeability reference standard, but lower than those of metoprolol and propranolol (both ranged from 8.49 to 11.6 × 10(-6) cm/s), low/high permeability boundary reference standards. Increasing buffer pH at the apical side from 5.5 to 8.0 gradually increased the absorptive permeation of mirabegron from 0.226 to 1.66 × 10(-6) cm/s, but was still less than the value in the opposite direction (11.0-14.2 × 10(-6) cm/s). The time- and concentration-dependent transport of mirabegron was observed in P-gp-expressing cells and OATP1A2-expressing oocytes with apparent Km values of 294 and 8.59 μM, respectively. In contrast, no clear BCRP-, MRP2-, PEPT1-, or OATP2B1-mediated uptake of mirabegron was observed in their expressing vesicles or cells. These findings suggest that mirabegron has low-to-moderate membrane permeability and P-gp is likely to be involved in its efflux into the lumen in the intestinal absorption process. The results also suggest that mirabegron could possibly be transported by intestinal influx transporters as well as simple diffusion.

New developments in the management of overactive bladder: focus on mirabegron and onabotulinumtoxinA

In the last few years, much new information has been generated on the pathophysiology, possible therapeutic targets, and pharmacologic treatment of overactive bladder (OAB). Antimuscarinic drugs are still first-line pharmacologic treatment for OAB and often have good initial response rates, but adverse effects and decreasing efficacy cause long-term compliance problems, prompting a search for new therapeutic alternatives. Mirabegron and onabotulinumtoxinA, two drugs with different mechanisms of action, and with adverse effect profiles different from those of antimuscarinics, were recently approved for treatment of OAB. However, their place in the treatment of this disorder has not yet been established. In this short review, the mechanisms of action, clinical efficacy, and safety profiles of these drugs are discussed and compared with those of the current gold standard, antimuscarinic agents.

Pharmacokinetic properties of mirabegron, a β3-adrenoceptor agonist: results from two phase I, randomized, multiple-dose studies in healthy young and elderly men and women

BACKGROUND

Mirabegron (YM178) is a β(3)-adrenoceptor agonist for the treatment of overactive bladder (OAB). As part of the clinical development program for mirabegron, 2 human volunteer studies were performed to derive detailed data on the multiple-dose pharmacokinetic (PK) properties of mirabegron.

OBJECTIVE

Two randomized Phase I studies were conducted to evaluate the PK properties of mirabegron, including metabolic profile and effects of age and sex, following multiple oral doses in healthy subjects.

METHODS

In study 1, mirabegron oral controlled absorption system (OCAS) tablets were administered once daily to healthy young subjects (18-55 years) at doses of 50, 100, 200, and 300 mg and in elderly subjects (65-80 years) at 50 and 200 mg in a double-blind placebo-controlled, parallel-group design. In study 2, mirabegron OCAS was administered once daily to healthy young (18-45 years) and older (≥55 years) subjects at doses of 25, 50, and 100 mg in an open-label crossover design. Blood samples were collected up to 72 hours (study 1) and 168 hours (study 2) after the last dose. Urine samples were collected up to 24 hours after the last dose. Plasma and urine concentrations of mirabegron and its metabolites (study 2 only) were analyzed by LC-MS/MS. PK parameters were determined using noncompartmental methods. Tolerability assessments included physical examinations, supine blood pressure and pulse rate, orthostatic stress testing (study 1), resting 12-lead ECGs, clinical laboratory tests (biochemistry, hematology, and urinalysis), and adverse-events (AE) monitoring using investigators' questionnaires and subjects' spontaneous reports.

RESULTS

Thirty-two young male (mean age, 30.3 years; mean weight, 77.1 kg), 32 young female (27.6 years; 64.6 kg), 16 elderly male (69.8 years; 79.3 kg), and 16 elderly female (68.1 years; 67.4 kg) subjects were enrolled in study 1. Eighteen young male (mean age, 28.6 years; mean weight, 68.9 kg), 18 young female (28.7 years; 58.8 kg), 21 older male (63.4 years; 72.6 kg), and 18 older female (65.1 years; 62.3 kg) subjects were enrolled in study 2. Most of the subjects were white (91% in study 1 and 88% in study 2). Mirabegron plasma concentrations peaked at ∼3 to 5 hours and declined multiexponentially with a t of ∼32 hours in study 1 and 60 hours in study 2. Steady state was achieved within 7 days of once daily administration, with an accumulation ratio of ∼2. Mirabegron and its metabolites demonstrated a greater-than-dose-proportional increase in C(max) and AUC(0-τ) after multiple-dose administration. Two major circulating metabolites were observed, representing 17% and 10% of total drug-related AUC(0-τ). Excretion of unchanged mirabegron in urine over the 24-hour dosing interval (Ae(0-τ)%) increased from approximately 7% at 25 mg to 18% at 300 mg once daily in young subjects. Renal clearance (CL(R)) of mirabegron was independent of dose and averaged ∼13 L/h. Mirabegron C(max) and AUC(0-τ) were similar in older and young subjects. Women exhibited ∼40% higher mirabegron C(max) and AUC(0-τ) than men; weight-corrected values were ∼20% higher in women. Mirabegron was generally well tolerated up to 300 mg once daily. No clear trends for increased incidence of AEs occurred with higher doses of mirabegron. The AE with the highest incidence was headache.

CONCLUSION

Oral mirabegron exhibited a greater-than-dose-proportional increase in exposure. Sex but not age significantly affected mirabegron exposure. ClinicalTrials.gov identifier: NCT01478503 (Study 1) and NCT01285596 (Study 2).