Selective Binding of Bladder Muscarinic Receptors in Relation to the Pharmacokinetics of a Novel Antimuscarinic Agent, Imidafenacin, to Treat Overactive Bladder

Pharmcokinetic and pharmacodynamic considerations for the anticholinergic burden scale of drugs

Older adults frequently have many systemic diseases that require treatment with multiple drugs, and thus anticholinergic adverse effect by polypharmacy is a significant concern in the management of older adults. The accuracy of the anticholinergic burden rating may be increased by considering pharmacokinetic and pharmacodynamic factors such as biophase drug concentrations, the pharmacologically active metabolites formed after drug administration, and muscarinic receptor-mediated effects. Therefore, a pharmacological evidence-based burden scale that considers pharmacokinetic and pharmacodynamic factors is expected to be a more optimal tool for precisely assessing the anticholinergic burden, specifically risk reductions in anticholinergic adverse events in the poly-medicated elderly. Geriatr Gerontol Int 2024; 24: 81-87.

Comparison of add-on medications for persistent storage symptoms after α-blocker treatment in BPH patients - a network meta-analysis

BACKGROUND

Patients with benign prostatic hyperplasia (BPH) receive α-blockers as first-line therapy to treat lower urinary tract symptoms; however, some individuals still experience residual storage symptoms. Antimuscarinics, β3-agonists, and desmopressin are effective add-on medications. Nevertheless, there is currently no evidence for the appropriate choice of the first add-on medication. This systematic review aimed to investigate the clinical benefits of antimuscarinics, β3-agonists, and desmopressin, in addition to α-blockers, for persistent storage symptoms in BPH patients.

METHODS

A comprehensive literature search of randomized controlled trials (RCTs) comparing the efficacy of different add-on medications in BPH patients with persistent storage symptoms despite α-blocker treatment was conducted. Clinical outcomes included the International Prostate Symptom Score (IPSS), IPSS storage subscore, nocturia, micturition, and urgency. A network meta-analysis was performed to estimate the effect size. Surface under cumulative ranking curves (SUCRAs) were used to rank the included treatments for each outcome.

RESULTS

A total of 15 RCTs were identified. Add-on imidafenacin and mirabegron resulted in significant improvement in all outcomes assessed. Other add-on medications such as desmopressin, tolterodine, solifenacin, fesoterodine, and propiverine showed positive benefits for most, but not all, outcomes. Based on the SUCRA rankings, add-on desmopressin was the best-ranked treatment for IPSS and nocturia, and add-on imidafenacin was the best for the IPSS storage subscore and micturition.

CONCLUSIONS

BPH patients presenting with persistent storage symptoms despite α-blocker administration are recommended to include additional treatment. Desmopressin and imidafenacin may be considered high-priority add-on treatments because of their superior efficacy compared with other medications.

The clinical pharmacology of the medical treatment for overactive bladder in adults

INTRODUCTION

Overactive bladder is a prevalent symptom complex that affects the patient's quality of life. Any disruption between the neuronal micturition pathway can lead to bladder overactivity. Neurogenic causes, myogenic causes, aging, bladder outlet obstruction, sex, and psychological factors are some of the factors contributing to bladder overactivity. The complaint of any symptoms of OAB, which is highly prevalent and affects overall QOL, often needs therapeutic interventions. When conservative therapy methods fail, the addition of medications is recommended. The most commonly used agents for the treatment of OAB are antimuscarinic drugs. New classes of drugs, such as beta-3 agonists, have enriched our pharmacologic armamentarium.

AREAS COVERED

In this review, with a special focus on oral pharmacological treatments, we discussed the definition, etiology, symptoms, diagnosis, and management of OAB.

EXPERT OPINION

OAB is a multifactorial condition with every patient presenting with a different collection of symptoms and signs. Medical therapies should be given in conjunction with behavioral therapies. Using high or low doses, flexible doses, and stopping or changing the medications are interchangeable strategies based on the level of treatment efficacy and patient satisfaction.

Is imidafenacin an alternative to current antimuscarinic drugs for patients with overactive bladder syndrome?

PURPOSE

Previous studies have included a limited number of randomized controlled trials (RCTs) and compared limited parameters after treatment with imidafenacin and other anticholinergic drugs (ADs) for overactive bladder syndrome (OAB), and controversy about the superiority of these ADs still remains. We aim to update the evidence and provide better clinical guidance.

METHODS

A systematic search of PubMed, Embase, ClinicalTrial.gov and Cochrane Library Central Register of Controlled Trials was conducted from January 2007 to April 2019. Meta-analysis of all published RCTs comparing imidafenacin with other ADs in patients with OAB was performed. The primary outcomes were the changes in OAB symptoms and OAB symptom score (OABSS). Secondary outcomes included adverse events (AEs) and the dropout rate related to AEs.

RESULTS

A total of 6 studies including 7 RCTs involving 1430 patients with mean follow-up of 23.43 weeks were included. All ADs improved OAB symptoms. Regarding efficacy, these drugs had similar efficacy in voids, urgency episodes, urgency incontinence episodes, incontinence episodes and OABSS. However, imidafenacin performed better in the reduction of nocturia episodes (MD = -0.24, 95% CI -0.44 to -0.04, P = 0.02). Moreover, imidafenacin was associated with a statistically lower dry mouth rate (RR = 0.87, 95% CI 0.75-1.00, P = 0.04), lower constipation rate (RR = 0.68, 95% CI 0.50-0.93, P = 0.01) and lower AE-related withdrawal rate (RR = 0.51, 95% CI 0.29-0.89, P = 0.02). There was no significant difference in terms of other complications.

CONCLUSIONS

In conclusion, imidafenacin was comparable to other ADs in the treatment of OAB. Moreover, imidafenacin presented a lower dry mouth rate, lower constipation rate and higher adherence and persistence.

Muscarinic receptor binding of fesoterodine, 5-hydroxymethyl tolterodine, and tolterodine in rat tissues after the oral, intravenous, or intravesical administration

The present study aimed to characterize muscarinic receptor binding of fesoterodine, 5-hydroxymethyl tolterodine (5-HMT), and tolterodine in bladder and other tissues of rats after their oral, intravenous, or intravesical administration. Muscarinic receptors in tissues were measured by using [N-methyl-³H]scopolamine methyl chloride ([³H]NMS). The in vitro binding affinity for muscarinic receptors was the highest by 5-HMT, followed by tolterodine and fesoterodine. Fesoterodine exhibited lower affinity in rat submaxillary gland than in detrusor muscle and urothelium. Muscarinic binding affinities of 5-HMT and tolterodine were similar among tissues. The duration of binding of oral fesoterodine to muscarinic receptors was longer in bladder than in submaxillary gland, heart, and lung, and its binding was little observed in colon and cerebral cortex. Binding activity of intravenous 5-HMT to muscarinic receptors was significantly observed in all tissues, except cerebral cortex, with a longer duration in bladder. Significant binding of bladder detrusor and urothelial muscarinic receptors was observed following intravesical instillation of 5-HMT. This selectivity may be attributed to the direct blockade of bladder receptors by excreted urinary 5-HMT. Thus, fesoterodine may be efficacious as a treatment for patients with overactive bladder.

Basic and clinical aspects of antimuscarinic agents used to treat overactive bladder

Antimuscarinic agents are now widely used as the pharmacological therapy for overactive bladder (OAB) because neuronal (parasympathetic nerve) and non-neuronal acetylcholine play a significant role for the bladder function. In this review, we will highlight basic and clinical aspects of eight antimuscarinic agents (oxybutynin, propiverine, tolterodine, solifenacin, darifenacin, trospium, imidafenacin, and fesoterodine) clinically used to treat urinary dysfunction in patients with OAB. The basic pharmacological characteristics of these eight antimuscarinic agents include muscarinic receptor subtype selectivity, functional bladder selectivity, and muscarinic receptor binding in the bladder and other tissues. The measurement of drug-receptor binding after oral administration of these agents allows for clearer understanding of bladder selectivity by the integration of pharmacodynamics and pharmacokinetics under in vivo conditions. Their central nervous system (CNS) penetration potentials are also discussed in terms of the feasibility of impairments in memory and cognitive function in elderly patients with OAB. The clinical aspects of efficacy focus on improvements in the daytime urinary frequency, nocturia, bladder capacity, the frequency of urgency, severity of urgency, number of incontinence episodes, OAB symptom score, and quality of life (QOL) score by antimuscarinic agents in patients with OAB. The safety of and adverse events caused by treatments with antimuscarinic agents such as dry mouth, constipation, blurred vision, erythema, fatigue, increased sweating, urinary retention, and CNS adverse events are discussed. A dose-dependent relationship was observed with adverse events, because the risk ratio generally increased with elevations in the drug dose of antimuscarinic agents. Side effect profiles may be additive to or contraindicated by other medications.

Characterization of muscarinic receptor binding by the novel radioligand, [(3)H]imidafenacin, in the bladder and other tissues of rats

The present study aimed to directly characterize specific binding sites of tritium ([(3)H])-labeled imidafenacin, a new radioligand for labeling muscarinic receptors, in the bladder and other peripheral or central nervous tissues of rats. Muscarinic receptors in rat tissues were measured by radioligand binding assay using [(3)H]imidafenacin. Specific [(3)H]imidafenacin binding in rat tissues was saturable, reversible, and of high affinity. Estimated dissociation constants (Kd values) were significantly lower in submaxillary gland and prostate and higher in heart than in bladder, indicating lower Kd values in M1 and M3 subtype- than M2 subtype-dominating tissues. Unlabeled imidafenacin and clinically used antimuscarinic agents competed with [(3)H]imidafenacin for binding sites in bladder and other tissues in a concentration-dependent manner, which indicated pharmacological specificity of [(3)H]imidafenacin binding sites. Pretreatment with N-(2-chloroethyl)-4-piperidinyl diphenylacetate (4-DAMP mustard), an irreversible inactivating agent of M3 subtype, significantly decreased the number of [(3)H]imidafenacin binding sites in bladder, submaxillary gland, and colon, but not in heart. [(3)H]imidafenacin labeled muscarinic receptors in M1 and M3 subtype-dominating tissues with higher affinity than [N-methyl-(3)H]scopolamine methyl chloride (NMS). [(3)H]imidafenacin is a useful radioligand to label muscarinic receptors in M1- and M3-dominating tissues with high affinity.

[Integration of pharmacokinetics and pharmacodynamics based on the in vivo analysis of drug-receptor binding]

  As I was deeply interested in the effects of drugs on the human body, I chose pharmacology as the subject of special study when I became a 4th year student at Shizuoka College of Pharmacy. I studied abroad as a postdoctoral fellow for two years, from 1978, under the tutelage of Professor Henry I. Yamamura (pharmacology) in the College of Medicine at the University of Arizona, USA. He taught me a variety of valuable skills such as the radioreceptor binding assay, which represented the most advanced technology developed in the US at that time. After returning home, I engaged in clarifying receptor abnormalities in pathological conditions, as well as in drug action mechanisms, by making the best use of this radioreceptor binding assay. In 1989, following the founding of the University of Shizuoka, I was invited by Professor Ryohei Kimura to join the Department of Pharmacokinetics. This switch in discipline provided a good opportunity for me to broaden my perspectives in pharmaceutical sciences. I worked on evaluating drug-receptor binding in vivo as a combined index for pharmacokinetics and pharmacological effect manifestation, with the aim of bridging pharmacology and pharmacokinetics. In fact, by focusing on data from in vivo receptor binding, it became possible to clearly rationalize the important consideration of drug dose-concentration-action relationships, and to study quantitative and kinetic analyses of relationships among pharmacokinetics, receptor binding and pharmacological effects. Based on this concept, I was able to demonstrate the utility of dynamic analyses of drug-receptor binding in drug discovery, drug fostering, and the proper use of pharmacokinetics with regard to many drugs.

Add-on anticholinergic therapy for residual nocturia in patients with lower urinary tract symptoms receiving α1-blocker treatment: a multi-centre, prospective, randomised study

PURPOSE

To evaluate the efficacy and safety of imidafenacin (IM), a novel short half-life anticholinergic, as add-on therapy for male LUTS with nocturia and nocturnal polyuria.

MATERIALS AND METHODS

This multicenter, prospective, randomized, open-labelled study was conducted and involved men who had frequency, urgency, and nocturia despite receiving a stable dose of α1-blocker for ≥1 month. Subjects were randomised to control (α1-blocker alone), IM twice/day (α1-blocker +0.1 mg imidafenacin twice daily), or IM nightly (α1-blocker plus 0.1 mg imidafenacin nightly) group; the treatment period was 8 weeks. Primary endpoints included improvements in night-time frequency and Nocturia Quality of Life Questionnaire (N-QOL) scores. Secondary endpoints included changes from the baseline in frequency volume chart variables, and post-void residual volume.

RESULTS AND LIMITATIONS

Compared with the controls, IM twice/day and IM nightly patients had a significantly lower night-time frequency (changes from baseline: 0.1 ± 0.8 in control, -0.6 ± 0.9 in IM twice/day, and -0.4 ± 1.0 in IM nightly, p = 0.5227, 0.0006 and 0.0143, respectively). The hours of undisturbed sleep and N-QOL score were significantly improved in IM twice/day group, though not IM nightly group. Nocturnal urine volume was significantly reduced in IM nightly group, although total urine volume remained unchanged.

CONCLUSIONS

A short half-life anticholinergic is suggested to be safe and effective as an add-on therapy for residual nocturia in patients with male LUTS receiving α1-blocker treatment. Anticholinergic administration nightly could reduce the nocturnal urine volume.

Muscarinic receptors mediate cold stress-induced detrusor overactivity in type 2 diabetes mellitus rats

OBJECTIVES

This study determined if muscarinic receptors could mediate the cold stress-induced detrusor overactivity induced in type 2 diabetes mellitus rats.

METHODS

Ten-week-old female Goto-Kakizaki diabetic rats (n = 12) and Wister Kyoto non-diabetic rats (n = 12) were maintained on a high-fat diet for 4 weeks. Cystometric investigations of the unanesthetized rats were carried out at room temperature (27 ± 2°C) for 20 min. They were intravenously administered imidafenacin (0.3 mg/kg, n = 6) or vehicle (n = 6). After 5 min, the rats were transferred to a low temperature (4 ± 2°C) for 40 min where the cystometry was continued. The rats were then returned to room temperature for the final cystometric measurements. Afterwards, expressions of bladder muscarinic receptor M3 and M2 messenger ribonucleic acids and proteins were assessed by reverse transcription polymerase chain reaction and immunohistochemistry.

RESULTS

In non-diabetic Wister Kyoto rats, imidafenacin did not reduce cold stress-induced detrusor overactivity. In diabetic Goto-Kakizaki rats, just after transfer to a low temperature, the cold stress-induced detrusor overactivity in imidafenacin-treated rats was reduced compared with vehicle-treated rats. Within the urinary bladders, the ratio of M3 to M2 receptor messenger ribonucleic acid in the diabetic Goto-Kakizaki rats was significantly higher than that of the non-diabetic Wister Kyoto rats. The proportion of muscarinic M3 receptor-positive area within the detrusor in diabetic Goto-Kakizaki rats was also significantly higher than that in non-diabetic Wister Kyoto rats.

CONCLUSIONS

Imidafenacin partially inhibits cold stress-induced detrusor overactivity in diabetic Goto-Kakizaki rats. In this animal model, muscarinic M3 receptors partially mediate cold stress-induced detrusor overactivity.

A randomised, prospective double-blind, propiverine-controlled trial of imidafenacin in patients with overactive bladder

AIM

To assess the efficacy and safety of imidafenacin compared with propiverine for treatment of overactive bladder (OAB) in Korean patients.

MATERIALS AND METHODS

Patients with OAB symptoms were randomised to double-blind treatment with 0.1 mg of imidafenacin twice daily (group A) or propiverine 20 mg once daily (group B) for 12-week regimen, and assessed for efficacy and safety. The primary efficacy outcome was per cent change of weekly urgency urinary incontinence (UUI) episodes at week 12. The secondary efficacy outcomes were changes in the micturitions per day, urine volume voided per micturition, urgency episodes per day, complete disappearance of incontinence episodes and severity of urgency from baseline to week 12. Quality of life and safety profiles were also compared.

RESULTS

Of 162 patients randomised, 140 completed the study protocol. The per cent change of weekly UUI episodes at week 12 was -69.1% in group A and -70.4% in group B (both p < 0.0001). The lower limit of 95% one-sided confidence interval of the difference between the groups was above the non-inferiority margin (-19.42%). Other voiding parameters and quality of life significantly improved at week 12 in both the groups. The discontinuation rates caused by adverse events were low in both the groups. While dry mouth was the most common adverse event (group A: 28.4% vs. B: 30.4%, p = 0.783), the severity of dry mouth was significantly less in the group A than B (p = 0.042) There were no significant differences in other safety profiles.

CONCLUSIONS

After the 12-week treatment of imidafenacin 0.1 mg twice daily, all OAB symptoms and quality of life improved. Imidafenacin was not inferior to propiverine for the reduction of UUI episodes, and was better tolerated than propiverine in the safety profile. Our results indicate that imidafenacin is a safe and effective drug in Korean patients with OAB.

A randomised, double-blind, parallel design, multi-institutional, non-inferiority phase IV trial of imidafenacin versus fesoterodine for overactive bladder

AIMS

Our objective was to compare the efficacy and safety of imidafenacin over fesoterodine in patients with overactive bladder (OAB).

METHODS

This study is a randomised, double-blind, parallel-group, fesoterodine-controlled study in patients with continuous OAB symptoms for ≥ 3 months, daily mean voiding frequency (DMVF) ≥ 8, and daily mean urgency or urgency incontinence frequency ≥ 2. A twice-daily 0.1 mg imidafenacin with placebo, or once-daily 4 mg fesoterodine with placebo were administered for 12 weeks. The primary efficacy end-point was the difference in DMVF at 12 weeks. The secondary efficacy end-points were differences in daily mean: (i) voiding frequency at 4 and 8 weeks; (ii) urgency frequency; (iii) urgency incontinence frequency; (iv) incontinence frequency; (v) nocturia frequency; and (vi) quality of life score. The variables for safety analysis were adverse events, vital signs, residual urine volume and clinical laboratory tests. An efficacy analysis was conducted in per-protocol patients and the safety analysis was conducted in all randomised patients.

RESULTS

The differences in DMVF at 12 weeks were -3.38 ± 3.63 and -2.45 ± 3.73 in the imidafenacin and fesoterodine groups, respectively, and the difference was not significant between the two groups. Imidafenacin was non-inferior to fesoterodine, and the lower limit of 95% two-sided confidence intervals was -0.53. The other six secondary end-points and variables for safety analysis showed no difference between the two groups.

CONCLUSIONS

Imidafenacin was non-inferior to fesoterodine in terms of efficacy, and showed no significant difference in terms of safety.

Fesoterodine, its active metabolite, and tolterodine bind selectively to muscarinic receptors in human bladder mucosa and detrusor muscle

OBJECTIVE

To comparatively characterize the binding activity of fesoterodine, its active metabolite (5-hydroxymethyl tolterodine [5-HMT]), and tolterodine in the human bladder mucosa, detrusor muscle, and parotid gland.

MATERIALS AND METHODS

Muscarinic receptors in the homogenates of human bladder mucosa, detrusor muscle, and parotid gland were measured by a radioligand binding assay using [N-methyl-(3)H] scopolamine methyl chloride.

RESULTS

Fesoterodine, 5-HMT, and tolterodine competed with [N-methyl-(3)H] scopolamine methyl chloride for binding sites in the bladder mucosa, detrusor muscle, and parotid gland in a concentration-dependent manner. The affinity for muscarinic receptors of these agents was significantly greater in the bladder than in the parotid gland, suggesting pharmacologic selectivity for the bladder over the parotid gland. The bladder selectivity was larger for fesoterodine and 5-HMT than for tolterodine. Fesoterodine, 5-HMT, and tolterodine resulted in significantly increased (two- to five-fold) values of the apparent dissociation constant for specific [N-methyl-(3)H] scopolamine methyl chloride binding in the detrusor muscle and parotid gland, with little effect on the corresponding values of the maximal number of binding sites. This finding indicates that these agents bind to the human muscarinic receptors in a competitive and reversible manner.

CONCLUSION

Fesoterodine and 5-HMT bind to the muscarinic receptors with greater affinity in the human bladder mucosa and detrusor muscle than in the parotid gland in a competitive and reversible manner.

Experience with imidafenacin in the management of overactive bladder disorder

Overactive bladder (OAB) is a chronic syndrome defined by symptoms of urinary urgency with no underlying medical causes. First-line treatment of OAB comprises fluid intake advice and bladder training, supplemented by anticholinergic drugs if necessary. Owing to the chronic nature of OAB, the ideal anticholinergic treatment should have good long-term efficacy and tolerability. There are many anticholinergics available, although some of these are not specific for the bladder and can cause adverse effects such as dry mouth, constipation, blurred vision or cognitive impairment. Imidafenacin (a newer anticholinergic which has been marketed in Japan since 2007) was developed to improve the tolerability of anticholinergic therapy. This article summarizes the pharmacological properties, pharmacokinetics, clinical efficacy and tolerability of imidafenacin in the treatment of OAB. Data from key clinical studies of imidafenacin show that it has a fast onset of action and is effective for the treatment of OAB. It selectively binds to muscarinic receptors in the bladder and is associated with a good safety profile compared with other anticholinergics. The clinical efficacy, superior tolerability and adjustable dosing of imidafenacin make it a good anticholinergic for the treatment of OAB.

Long-term safety, efficacy, and tolerability of imidafenacin in the treatment of overactive bladder: a review of the Japanese literature

Imidafenacin is an antimuscarinic agent with high affinity for the M(3) and M(1) muscarinic receptor subtypes and low affinity for the M(2) subtype, and is used to treat overactive bladder. Several animal studies have demonstrated that imidafenacin has organ selectivity for the bladder over the salivary glands, colon, heart, and brain. In Phase I studies in humans, the approximately 2.9-hour elimination half-life of imidafenacin was shorter than that of other antimuscarinics such as tolterodine and solifenacin. Imidafenacin was approved for clinical use in overactive bladder in Japan in 2007 after a randomized, double-blind, placebo-controlled Phase II study and a propiverine-controlled Phase III study conducted in Japanese patients demonstrated that imidafenacin 0.1 mg twice daily was clinically effective for treating overactive bladder and was not inferior to propiverine for reduction of episodes of incontinence, with a better safety profile than propiverine. Several short-term clinical studies have demonstrated that imidafenacin also improves sleep disorders, nocturia, and nocturia-related quality of life. In addition, it is speculated that addon therapy with imidafenacin is beneficial for men with benign prostatic hyperplasia whose overactive bladder symptoms are not controlled by alpha-1 adrenoceptor antagonists. No cognitive impairment or influence of imidafenacin on the QTc interval has been observed. Although there have been very few relevant long-term clinical studies, the available information suggests the long-term efficacy, safety, and tolerability of imidafenacin, with less frequent severe adverse events, such as dry mouth and constipation. In addition, imidafenacin can be used safely for a long time even for cognitively vulnerable elderly patients with symptoms of overactive bladder. Thus, it is highly likely that imidafenacin is safe, efficacious, and tolerable to control symptoms of overactive bladder even over the long term. However, it remains unknown if the practical effectiveness of imidafenacin is applicable to ethnic groups other than Japanese.

Characterization of bladder selectivity of antimuscarinic agents on the basis of in vivo drug-receptor binding

The in vivo muscarinic receptor binding of antimuscarinic agents (oxybutynin, solifenacin, tolterodine, and imidafenacin) used to treat urinary dysfunction in patients with overactive bladder is reviewed. Transdermal administration of oxybutynin in rats leads to significant binding of muscarinic receptors in the bladder without long-term binding in the submaxillary gland and the abolishment of salivation evoked by oral oxybutynin. Oral solifenacin shows significant and long-lasting binding to muscarinic receptors in mouse tissues expressing the M₃ subtype. Oral tolterodine binds more selectively to muscarinic receptors in the bladder than in the submaxillary gland in mice. The muscarinic receptor binding of oral imidafenacin in rats is more selective and longer-lasting in the bladder than in other tissues such as the submaxillary gland, heart, colon, lung, and brain, suggesting preferential muscarinic receptor binding in the bladder. In vivo quantitative autoradiography with (+)N-[¹¹C]methyl-3-piperidyl benzilate in rats shows significant occupancy of brain muscarinic receptors with the intravenous injection of oxybutynin, solifenacin, and tolterodine. The estimated in vivo selectivity in brain is significantly greater for solifenacin and tolterodine than for oxybutynin. Imidafenacin occupies few brain muscarinic receptors. Similar findings for oral oxybutynin were observed with positron emission tomography in conscious rhesus monkeys with a significant disturbance of short-term memory. The newer generation of antimuscarinic agents may be advantageous in terms of bladder selectivity after systemic administration.

Comparative Evaluation of the Safety and Efficacy of Long-Term Use of Imidafenacin and Solifenacin in Patients with Overactive Bladder: A Prospective, Open, Randomized, Parallel-Group Trial (the LIST Study)

Objectives. Overactive bladder (OAB) is a chronic disease, but comparative trials of anticholinergics, which are commonly used for treatment of OAB, have generally been performed for up to 12 weeks only. There is no comparative study of a long-term intervention. Methods. We conducted a 52-week prospective randomized comparative study to evaluate the efficacy and tolerability of two anticholinergics. Results. Forty-one Japanese patients with untreated OAB were randomly assigned to imidafenacin and solifenacin groups. There was no difference in OABSS and KHQ scores between the two groups, but the severity and incidence of adverse events caused by the anticholinergics showed increased differences between the groups with time. The severity of dry mouth and the incidence of constipation were significantly lower in the imidafenacin group (P = 0.0092 and P = 0.0013, resp.). Conclusions. This study is the first long-term trial to show differences in the properties of anticholinergics that were not detected in short-term studies. Since OAB is a chronic disease, we conclude that imidafenacin is preferable to solifenacin from a perspective of safety.

In vivo bladder selectivity of imidafenacin, a novel antimuscarinic agent, assessed by using an effectiveness index for bladder capacity in rats

Imidafenacin (KRP-197) is a novel antimuscarinic agent for overactive bladder treatment. The inhibitory effect of imidafenacin on detrusor contraction has been adopted for assessing their bladder selectivity, but this is becoming less convincing as an effectiveness index. We, therefore, reevaluated the bladder selectivity of imidafenacin and other antimuscarinics using their effects on the bladder capacity as an effectiveness index. Bladder capacity was measured by intermittent cystometry in urethane-anesthetized rats. In the tissues related to antimuscarinic side effects, the inhibitory actions were measured each on salivary secretion by electrical stimulation of chorda tympani, on rhythmical contractions in colon, and on carbamylcholine-induced bradycardia. Imidafenacin, solifenacin succinate, tolterodine tartrate, and propiverine hydrochloride significantly increased the bladder capacity, with minimum effective doses of 0.003, 1, 0.03, and 3 mg/kg (i.v.), respectively. The antimuscarinics tested, except for propiverine hydrochloride, shared a common property of increasing bladder capacity at a dose which did not affect micturition pressure. The relative bladder selectivity of imidafenacin, solifenacin succinate, and tolterodine tartrate was 15-, 1.7-, and 2.5-fold higher over salivary gland; 150-, 1.9-, and 9.2-fold higher over colon; and 50-, 12-, and 4.6-fold higher over heart, respectively, than that of propiverine hydrochloride. Thus, imidafenacin shows the most highly selective for bladder over the tissues related to major antimuscarinic side effects, compared to the other three well-known antimuscarinics tested in the rat.

α1-Adrenoceptors and muscarinic receptors in voiding function - binding characteristics of therapeutic agents in relation to the pharmacokinetics

In vivo and ex vivo binding of α(1)-adrenoceptor and muscarinic receptors involved in voiding function is reviewed with therapeutic agents (α(1)-adrenoceptor antagonists: prazosin, tamsulosin and silodosin; and muscarinic receptor antagonists: oxybutynin, tolterodine, solifenacin, propiverine, imiafenacin and darifenacin) in lower urinary tract symptoms. This approach allows estimation of the inhibition of a well-characterized selective (standard) radioligand by unlabelled potential drugs or direct measurement of the distribution and receptor binding of a standard radioligand or radiolabelled form of a novel drug. In fact, these studies could be conducted in various tissues from animals pretreated with radioligands and/or unlabelled novel drugs, by conventional radioligand binding assay, radioactivity measurement, autoradiography and positron emission tomography. In vivo and ex vivo receptor binding with α(1)-adrenoceptor antagonists and muscarinic receptor antagonists have been proved to be useful in predicting the potency, organ selectivity and duration of action of drugs in relation to their pharmacokinetics. Such evaluations of drug-receptor binding reveal that adverse effects could be avoided by the use of new α(1)-adrenoceptor antagonists and muscarinic receptor antagonists for the treatment of lower urinary tract symptoms. Thus, the comparative analysis of α(1)-adrenoceptor and muscarinic receptor binding characteristics in the lower urinary tract and other tissues after systemic administration of therapeutic agents allows the rationale for their pharmacological characteristics from the integrated viewpoint of pharmacokinetics and pharmacodynamics. The current review emphasizes the usefulness of in vivo and ex vivo receptor binding in the discovery and development of novel drugs for the treatment of not only urinary dysfunction but also other disorders.