Absolute bioavailability of imidafenacin after oral administration to healthy subjects

Bladder and Bowel Management in Dogs With Spinal Cord Injury

Spinal cord injury in companion dogs can lead to urinary and fecal incontinence or retention, depending on the severity, and localization of the lesion along the canine nervous system. The bladder and gastrointestinal dysfunction caused by lesions of the autonomic system can be difficult to recognize, interpret and are easily overlooked. Nevertheless, it is crucial to maintain a high degree of awareness of the impact of micturition and defecation disturbances on the animal's condition, welfare and on the owner. The management of these disabilities is all the more challenging that the autonomic nervous system physiology is a complex topic. In this review, we propose to briefly remind the reader the physiology of micturition and defecation in dogs. We then present the bladder and gastrointestinal clinical signs associated with sacral lesions (i.e., the L7-S3 spinal cord segments and nerves) and supra-sacral lesions (i.e., cranial to the L7 spinal cord segment), largely in the context of intervertebral disc herniation. We summarize what is known about the natural recovery of urinary and fecal continence in dogs after spinal cord injury. In particular we review the incidence of urinary tract infection after injury. We finally explore the past and recent literature describing management of urinary and fecal dysfunction in the acute and chronic phase of spinal cord injury. This comprises medical therapies but importantly a number of surgical options, some known for decades such as sacral nerve stimulation, that might spark some interest in the field of spinal cord injury in companion dogs.

Imidafenacin, An Orally Active Muscarinic Receptor Antagonist, Improves Pulmonary Function In Patients With Chronic Obstructive Pulmonary Disease: A Multicenter, Randomized, Double-Blind, Placebo-Controlled 3×3 Crossover Phase II Trial

Background

Although long-acting muscarinic receptor antagonists are central to the management of chronic obstructive pulmonary disease (COPD), inhaled medicines may have technical difficulty in some patients and adherence barriers.

Methods

A multicenter, randomized, double-blind, placebo-controlled 3×3 crossover Phase II trial was performed to evaluate the efficacy and safety of oral administration of the antimuscarinic agent imidafenacin in patients with COPD. Twenty-seven male COPD patients with % forced expiratory volume in 1 s (FEV₁) ≥30% and <80% predicted were randomized to single oral dose of imidafenacin 0.1 mg, imidafenacin 0.2 mg, or placebo.

Results

Maximum change in FEV₁ with both doses of imidafenacin significantly improved from baseline to 24 hrs after administration when compared with a placebo. Area under the curve in FEV₁ during 24 hrs after administration with 0.2 mg, but not 0.1 mg dose, was significantly improved when compared with a placebo, and the improvement was significantly based on dose-dependent manners. Plasma imidafenacin level was positively correlated with change in FEV₁. All subjects with both doses of imidafenacin completed without moderate nor severe adverse events.

Conclusion

A single oral dose of imidafenacin 0.1 mg or imidafenacin 0.2 mg may contribute to the improvement of pulmonary function with excellent safety and tolerability in patients with COPD.

Trial registration

JapicCTI-121760 (Japan Pharmaceutical Information Center – Clinical Trials Information [JapicCTI]; http://www.clinicaltrials.jp/user/cteSearch_e.jsp).

Novel Extended-Release Multiple-Unit System of Imidafenacin Prepared by Fluid-Bed Coating Technique

The objective of this study was to formulate once-a-day extended-release (ER) pellet system of imidafenacin (IDN), a recently approved urinary antispasmodic agent with twice-a-day dosing regimen. The sugar sphere pellets were firstly layered with IDN and hypromellose and then coated with Eudragit RS (copolymers of acrylic and methacrylic acid esters), employed as a release modifier, using a fluid-bed coater. Solid-state characterizations using solid-state X-ray diffraction and differential scanning calorimeter indicated that the antispasmodic agent was homogeneously layered onto the pellets in an amorphous state. Drug release from multiple-unit ER system was effectively retarded in proportion to the amount of Eudragit RS in the outer layer, with a high correlation value above 0.86. In a pharmacokinetic evaluation in beagle dogs, the plasma concentration profile of IDN was markedly protracted by ER pellets, exhibiting delayed the time needed to reach the maximum drug concentration and the elimination half-life in plasma, compared to the commercial immediate release form (Uritos® tablet, Kyorin Pharmaceutical Co., Ltd., Japan). Therefore, the novel ER pellets can be a promising tool for oral IDN therapy, providing a once-a-day dosing regimen, and thus, improving patient compliance.

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.

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.

Population pharmacokinetics and exposure-response relationship of a muscarinic receptor antagonist, imidafenacin

This study was designed to update the population pharmacokinetic model and investigate the exposure-response (efficacy and safety) and concentration-QT relationships for imidafenacin, a synthetic orally active muscarinic receptor antagonist. The population pharmacokinetic model was updated using data from 90 healthy subjects and 852 patients with an overactive bladder. Plasma concentration data from nine clinical studies were used, including new data from a long-term dose escalation study. The updated population pharmacokinetic model for imidafenacin adequately described the plasma concentration profile. The results were generally consistent with those obtained from the previous population pharmacokinetic analysis, indicating that no new covariates were found to influence the pharmacokinetics of imidafenacin. Exposure-response relationships in the long-term dose escalation study were investigated using a regression analysis with efficacy and safety endpoints as dependent variables. There was no clear relationship between exposure and any endpoint. The concentration-QT relationship was also evaluated to assess whether imidafenacin prolonged the concentration-dependent QT interval. There was no clear relationship between the plasma concentration of imidafenacin and QTc, indicating that concentration-dependent QTc interval prolongation was not observed.

Pharmacokinetics and toxicity of antimuscarinic drugs for overactive bladder treatment in females

INTRODUCTION

Antimuscarinics (AMs) are the mainstay of pharmacological treatment of overactive bladder (OAB), a symptom complex defined by the presence of urinary urgency, usually associated with frequency and nocturia, with or without urgency urinary incontinence. The AMs used to treat OAB differ in their pharmacological profiles, which may affect their potential for causing adverse effects (AEs).

AREAS COVERED

The present article aims to review the literature about pharmacokinetics (PK) of the different AMs used in the treatment of OAB. Furthermore, the AEs related to the use of these drugs and their incidence are presented. This systematic review is based on material searched and obtained via Medline, Pubmed and EMBASE up to March 2012 using the search terms "adverse events, pharmacokinetics, tolerability" in combination with "darifenacin, fesoterodine, imidafenacin, oxybutynin, propiverine, solifenacin, tolterodine, and trospium."

EXPERT OPINION

Antimuscarinics are the first-line pharmacological treatment for OAB. Despite the development of new molecules that improve their efficacy/safety profile, there are some drugs that are pharmacokinetically more appropriate to be prescribed in specific populations such as patients with neurological disease or the elderly. Moreover, research should be encouraged in evaluating antimuscarinics in conjunction with other drugs such as estrogens or beta-agonists. The identification of prognostic criteria for pharmacological therapy would be helpful.

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.

Immediate effect on overactive bladder symptoms following administration of imidafenacin

INTRODUCTION

One of the factors influencing the treatment compliance of patients with overactive bladder (OAB) symptoms is thought to be the time to reach clinical effectiveness after administering drugs. We investigated the immediate effect of imidafenacin on OAB symptoms.

PATIENTS AND METHODS

Imidafenacin (0.1 mg) was administered. OAB symptom scores (OABSS) were evaluated before administration, and at 2 and 4 weeks after administration. The subjective efficacy in patients was examined by recording daily changes for 2 weeks.

RESULTS

Twenty patients were evaluated for efficacy using OABSS and uroflowmetry with postvoid residual volume. Nineteen patients completely recorded daily changes in subjective efficacy. The mean total OABSS decreased gradually during 2 weeks after administration. Patients reported the drug's efficacy to begin 3 days after the commencement of administration. Urinary flow and postvoid residual volume did not change after administration.

CONCLUSION

The subjective efficacy of imidafenacin was observed from 3 days after the commencement of administration.

Medicinal chemistry and therapeutic potential of muscarinic M3 antagonists

Muscarinic acetylcholine receptors belong to the G-protein-coupled receptors family. Currently five different receptor subtypes have been identified and cloned. M3 receptor subtypes are coupled to G(q) family proteins and increase phosphatidyl inositol hydrolysis and calcium release from internal stores. They are widely distributed both in the central nervous system and in the periphery. At the central level, M3 receptor subtypes are involved in modulation of neurotransmitter release, temperature homeostasis, and food intake, while in the periphery they induce smooth muscle contraction, gland secretion, indirect relaxation of vascular smooth muscle, and miosis. The main therapeutic applications of M3 antagonists include overactive bladder (OAB), chronic obstructive pulmonary disease (COPD), and pain-predominant irritable bowel syndrome (IBS). The introduction of selective M3 antagonists has not improved clinical efficacy compared with the old non-selective antimuscarinics but has reduced the rate of adverse events mediated by the blockade of cardiac M2 receptors (tachycardia) and central M1 receptors (cognitive impairment). Improved tolerability has been obtained also with controlled release or with inhaled formulations. However, there is still a need for safer M3 antagonists for the treatment of COPD and better-tolerated and more effective compounds for the therapy of OAB. New selective muscarinic M3 antagonists currently in early discovery and under development have been designed to address these issues. However, as M3 receptors are widely located in various tissues including salivary glands, gut smooth muscles, iris, and ciliary muscles, further clinical improvements may derive from the discovery and the development of new compounds with tissue rather than muscarinic receptor subtype selectivity.

Absorption, Metabolism, and Excretion of [14C]Imidafenacin, a New Compound for Treatment of Overactive Bladder, After Oral Administration to Healthy Male Subjects

The absorption, metabolism, and excretion of imidafenacin [KRP-197/ONO-8025, 4-(2-methyl-1H-imidazol-1-yl)-2,2-diphenylbutanamide], a new antimuscarinic drug developed for treatment of overactive bladder, were assessed in six healthy male subjects after a single oral administration of 0.25 mg of [(14)C]imidafenacin (approximately 46 microCi). The highest radioactivity in the plasma was observed at 1.5 h after administration. The apparent terminal elimination half-life of the total radioactivity was 72 h. Approximately 65.6 and 29.4% of the administered radioactivity were recovered in the urine and feces, respectively, within 192 h after administration. The metabolite profiling by high-performance liquid chromatography-radiodetector and liquid chromatography/tandem mass spectrometry demonstrated that the main component of radioactivity was unchanged imidafenacin in the 2-h plasma. The N-glucuronide conjugate (M-9) was found as the major metabolite and the oxidized form of the 2-methylimidazole moiety (M-2) and the ring-cleavage form (M-4) were detected as the minor metabolites in the 2-h plasma, but M-4 was found to be the main component in the 12-h plasma. Unchanged imidafenacin, M-9, M-2, and other oxidized metabolites were excreted in the urine, but the unchanged imidafenacin and M-9 were not found in the feces. Two unique metabolites were found in the urine and feces, which were identified as the interchangeable cis- and trans-isomers of 4,5-dihydrodiol forms of the 2-methylimidazole moiety. These findings indicate that imidafenacin is rapidly and well absorbed (at least 65% of dose recovered in urine) after oral administration, circulates in human plasma as the unchanged form, its glucuronide, and other metabolites, and is then excreted in urine and feces as the oxidized metabolites of 2-methylimidazole moiety.