Safety assessment of prucalopride in elderly patients with constipation: a double-blind, placebo-controlled study

Irritable bowel syndrome: recent developments in diagnosis, pathophysiology, and treatment

The diagnosis of irritable bowel syndrome (IBS) remains a diagnosis of exclusion, whereby an extensive investigation is performed to exclude other organic diseases that may explain the symptoms of patients. Attempts to have a positive diagnosis based on symptom assessments failed to achieve widely use in clinical practice. Abnormalities in the gastrointestinal endocrine cells in IBS patients have been reported recently, providing evidence that IBS is an organic disorder, and opening the door to the use of these abnormalities as markers for a positive diagnosis of IBS. New and promising drugs for the treatment of IBS with constipation as the predominant symptom are currently on the market, and the treatment results have been satisfactory thus far.

New pharmacological treatment options for chronic constipation

INTRODUCTION

A number of new medications were recently demonstrated to be more effective than placebo in treating chronic constipation, including the intestinal chloride channel activator lubiprostone, the prokinetic selective 5-HT4 receptor agonist prucalopride and the guanylate cyclase-C agonist linaclotide. Recent publications have also revisited traditional laxatives like PEG. Moreover, a number of pharmacological treatments are in development and these include another guanylate cyclase-C agonist, plecanatide and an ileal bile acid transporter inhibitor, elobixibat.

AREAS COVERED

This review focuses on the pharmacology, efficacy and safety profile of prucalopride, linaclotide, plecanatide and elobixibat.

EXPERT OPINION

The possible present or future clinical application of prucalopride, linaclotide, plecanatide and elobixibat in both chronic constipation and irritable bowel syndrome with constipation is reported, and some considerations on the possible role of PEG taking into account recent literature are advanced.

Systematic review with meta-analysis: highly selective 5-HT4 agonists (prucalopride, velusetrag or naronapride) in chronic constipation

BACKGROUND

Highly selective 5-HT4 agonists have been suggested for the treatment of chronic constipation (CC).

AIM

To assess the effects of highly selective 5-HT4 agonists (prucalopride, velusetrag or naronapride) on patient-important clinical efficacy outcomes and safety in adults with CC.

METHODS

We searched the medical literature in January 2013 using MEDLINE/Pubmed, Embase, Cochrane Library, and Web of Science/Scopus for randomised, controlled trials of highly selective 5-HT4 agonists in adults with CC, with no minimum duration of therapy (maximum 12 weeks) or date limitations. Data were extracted from intention-to-treat analyses, pooled using a random-effects model, and reported as relative risk (RR), mean differences, or standardised mean differences with 95% confidence intervals (CI).

RESULTS

Main outcomes included stool frequency, Patient-Assessment of Constipation Quality of Life (PAC-QOL), PAC of symptoms (PAC-SYM) and adverse events. Thirteen eligible trials were identified: 11 prucalopride, 1 velusetrag, 1 naronapride. Relative to control, treatment with highly selective 5-HT4 agonists was superior for all outcomes: mean ≥3 spontaneous complete bowel movements (SCBM)/week (RR = 1.85; 95% CI 1.23-2.79); mean ≥1 SCBM over baseline (RR = 1.57; 95% CI 1.19, 2.06); ≥1 point improvement in PAC-QOL and PAC-SYM scores. The only active comparator trial of prucalopride and PEG3350 suggested PEG3350 is more efficacious for some end points. Adverse events were more common with highly selective 5-HT4 agonists, but were generally minor; headache was the most frequent. Most trials studied prucalopride.

CONCLUSION

Demonstration of efficacy on patient-important outcomes and a favourable safety profile support the continued use and development of highly selective 5-HT4 agonists in the treatment of chronic constipation.

Chronic constipation and treatment options (Review)

Chronic constipation (CC) is a highly prevalent heterogeneous disorder. Although CC is not known to be associated with the development of serious disease or with excess mortality, it considerably reduces the patients quality of life. In addition, it represents an economic burden to patients and society. The majority of patients with CC successfully manage the disorder by dietary management and the use of laxatives. Patients with functional CC (slow‑transit and non‑slow transit constipation) do not respond to laxatives and are a small fraction of the total population complaining of constipation. Regardless of the low number of these patients, the intractability of their symptoms causes psychological and social stress and greatly impairs their quality of life. Furthermore, these patients consume a disproportionate quantity of medical resources. It appears that these patients have a disturbance in the serotonin transmission system, which results in a cascade of alterations in a number of gut neuroendocrine hormones/transmitters. The effect of prucalopride, a serotonin receptor agonist, in this category of patients appears to be not only a pharmacological prokinetic action, but also a correction of a pre‑existing disturbance. Linaclotide, a member of the guanylin peptide family, binds to the ligand‑binding region of guanylate cyclase‑C on the luminal surface of gastrointestinal epithelia resulting in increased fluid secretion. This drug has also been found to be effective for the treatment of functional CC. In addition, biofeedback and sacral nerve stimulation are effective in the treatment of CC caused by pelvic floor disorders.

Linaclotide: a new option for the treatment of irritable bowel syndrome with constipation and chronic idiopathic constipation in adults

Chronic idiopathic constipation (CC) and irritable bowel syndrome with predominant constipation (IBS-C) are the 2 most common conditions among functional gastrointestinal disorders. Despite current multiple therapeutic options, treatment remains challenging and dissatisfactory to many patients. Linaclotide is a novel therapeutic agent, which is a guanylate cyclase receptor agonist that stimulates water secretion from the intestinal epithelium by promoting chloride and bicarbonate efflux into the lumen through activation of the cystic fibrosis transmembrane conductance regulator. Clinical trials have demonstrated that linaclotide is effective, safe and well tolerated in patients with CC and IBS-C. This review article highlights the mechanism of action of linaclotide, reviews published literature based on a search of databases, including MEDLINE, EMBASE, and Cochrane Central Register of Controlled Trials (CENTRAL), up to February 2013, and compares its utility with other currently available agents.

The effects of prucalopride on postoperative ileus in guinea pigs

PURPOSE

Postoperative ileus (POI) is an impairment of coordinated gastrointestinal (GI) motility that develops as a consequence of abdominal surgery and is a major factor contributing to patient morbidity and prolonged hospitalization. The aim of this study was to investigate the effects of different 5-hydroxytryptamine 4 (5-HT₄) receptor agonists, which stimulate excitatory pathways, on a POI model.

MATERIALS AND METHODS

The experimental model of POI in guinea pigs was created by laparotomy, gentle manipulation of the cecum for 60 seconds, and closure by suture, all under anesthesia. Different degrees of restoration of GI transit were measured by the migration of charcoal. Colonic transit was indirectly assessed via measurement of fecal pellet output every hour for 5 hours after administration of various doses of mosapride, tegaserod, prucalopride, and 5-HT.

RESULTS

Charcoal transit assay showed that various 5-HT₄ receptor agonists can accelerate delayed upper GI transit in a dose-dependent manner. However, fecal pellet output assay suggested that only prucalopride had a significant effect in accelerating colonic motility in POI.

CONCLUSION

Although mosapride, tegaserod, and prucalopride produce beneficial effects to hasten upper GI transit in the POI model, prucalopride administered orally restores lower GI transit as well as upper GI transit after operation in a conscious guinea pig. This drug may serve as a useful candidate for examination in a clinical trial for POI.

Pharmacokinetic and pharmacodynamic considerations for the current chronic constipation treatments

INTRODUCTION

Chronic constipation is a frequent condition often treated pharmacologically. The laxatives available belong to very different pharmacologic groups.

AREAS COVERED

This is a short but comprehensive review of the pharmacology, efficacy and safety of currently available laxatives for chronic constipation. Pertinent publications were retrieved from reference lists of publications and by literature searches via PubMed, lastly performed in November 2012.

EXPERT OPINION

The most relevant laxative groups are the older representatives osmotic salts, sugars and sugar alcohols, macrogol, anthraquinones, diphenolic laxatives or diphenyl methanes (bisacodyl and sodium picosulfate) and the newer compounds prucalopride, lubiprostone and linaclotide. For all of these laxatives efficacy has been shown in controlled trials. Electrolyte losses do not occur when laxatives are given in therapeutic doses (rare exceptions with phosphate salts and salinic laxatives). The older laxatives are also safe regarding teratogenicity, abortion and lactation. For the newer compounds no respective data are available as yet. It is questionable whether the newer compounds offer advantages over the older ones. Unfortunately, comparative trials are lacking.

A critical appraisal of lubiprostone in the treatment of chronic constipation in the elderly

Chronic constipation is a common disorder in the general population, with higher prevalence in the elderly, and is associated with worse quality of life and with greater health care utilization. Lubiprostone is an intestinal type-2 chloride channel activator that increases intestinal fluid secretion, small intestinal transit, and stool passage. Lubiprostone is currently approved by the US Food and Drug Administration for the treatment of chronic idiopathic constipation and of irritable bowel syndrome with predominant constipation. This review outlines current approaches and limitations in the treatment of chronic constipation in the elderly and discusses the results, limitations, and applicability of randomized, controlled trials of lubiprostone that have been conducted in the general and elderly population, with additional focus on the use of lubiprostone in constipation in Parkinson's disease and in opioid-induced constipation, two clinical entities that can be comorbid in elderly patients.

Prucalopride: evaluation of the pharmacokinetics, pharmacodynamics, efficacy and safety in the treatment of chronic constipation

INTRODUCTION

Prucalopride is the first member of a novel class of 5-HT(4) receptor agonist which has been extensively evaluated for the treatment of chronic constipation. Predominantly, prucalopride is currently used to treat patients that show an insufficient response to laxatives as an alternative form of therapy.

AREAS COVERED

The following article provides the reader with a systematic review of the literature on prucalopride. Specifically, the article reviews the currently literature on the pharmacokinetics and the pharmacodynamics of the drugs as well as reviewing literature on its efficacy. Furthermore, the authors also highlight the safety and tolerability of the drug that have been demonstrated in its clinical development.

EXPERT OPINION

Prucalopride is an important addition to the therapeutic abilities for treating chronic constipation, especially in females poorly responding to laxatives. The safety profile of the drug, to date, is favorable. There is also the possibility that prucalopride might be of benefit to other disorders of gastrointestinal motility with a number of studies currently in progress, which are evaluating alternative applications.

Metabolic and toxicological considerations for the latest drugs used to treat irritable bowel syndrome

INTRODUCTION

The high prevalence of irritable bowel syndrome (IBS), a chronic gastrointestinal (GI) disorder, its lack of satisfactory effective drugs and its complicated pathophysiology lead to the demand of new therapeutic agents. During a new drug development process, the pharmacokinetic profiling is of a great considerable importance comparable to drug's efficacy. This involves the drug's absorption, distribution, metabolism and excretion, all of which are crucial to its usefulness. In addition, the toxicological profile and possible adverse reactions of the drug should be identified. Also its interactions should be identified at different phases of trials. Several pharmacokinetic studies are carried out to achieve drugs with the best absorption and bioavailability and the least adverse effects and lowest toxicity.

AREAS COVERED

To make an update on new clinically introduced drugs for IBS and their dynamics and kinetics data, the present systematic review was accomplished. All relevant bibliographic databases were searched from the year 2003 up to May 2012 to identify all clinical trials that evaluated the potential efficacy of a novel agent in IBS.

EXPERT OPINION

Some evaluated drugs, such as ramosetron (5-HT3 antagonist) and pexacerfont (CRF1 receptor antagonist), have shown some benefits in diarrhea-predominant IBS (D-IBS), while, prucalopride and mosapride (5-HT4 agonist) with prokinetic effect were found useful in constipation-predominant IBS (C-IBS). Besides, dexloxiglumide, lubiprostone and linaclotide have shown beneficial effects in C-IBS patients. Melatonin regulates GI tract motility and, asimadoline, gabapentin and pregabalin show reduction of pain threshold and visceral hypersensitivity. Glucagon-like peptide analog, calcium-channel blockers and neurokinin receptor antagonists have shown benefits in pain attacks. More time is required to indicate both efficacy and safety in long-term treatment due to multifactorial pathophysiology, variations in individual responses and insufficient assessment methods, which limit the right decision-making process about the efficacy and tolerability of these new drugs.

Physiology of the ageing gut

PURPOSE OF REVIEW

This article will review the recent publications (over the last 1-2 years) concerning the effects of ageing on gastrointestinal function, with an emphasis on the motor and sensory function of the gut.

RECENT FINDINGS

Recent publications support earlier observations of an age-related selective decline in the number of cholinergic neurons in the enteric nervous system, but also reveal a progressive loss of interstitial cells of Cajal in the stomach and colon throughout adult life. These changes appear to have surprisingly little effect on gastrointestinal motor function in healthy ageing, although gut sensation is impaired and older individuals have an increased susceptibility to gastrointestinal complications of comorbid illnesses.

SUMMARY

Alterations in gut function with ageing have particular implications in the oesophagus, colon, and anorectum. Dysphagia, gastro-oesophageal reflux disease, constipation, and faecal incontinence are the most prevalent clinical manifestations. Older individuals are also susceptible to postprandial hypotension, in which altered cardiovascular responses to intestinal nutrient exposure are pivotal. Dysphagia, delayed gastric emptying, and constipation are increasingly being recognized as early features of Parkinson's disease, and frequently precede the neurological manifestations.

Elobixibat for the treatment of constipation

INTRODUCTION

Elobixibat (formerly A3309) is a first-in-class ileal bile acid transporter (IBAT) inhibitor for treatment of chronic idiopathic constipation (CIC; syn functional constipation). CIC affects up to 25% of the general population; and up to a half are unsatisfied with current therapies. There is an unmet need for safe and effective drugs to treat CIC.

AREAS COVERED

The authors present: i) an overview of Phase II clinical trials of elobixibat in CIC, based on peer-reviewed literature and congress presentations and ii) an evaluation of the efficacy and mechanism of action of elobixibat in the treatment of CIC.

EXPERT OPINION

Elobixibat provides a novel approach to treat chronic constipation via IBAT inhibition with enhanced delivery of bile acids to the colon. Pharmacodynamic studies show that it accelerates colonic transit, increases stool frequency, loosens stool consistency and relieves constipation-related symptoms in CIC patients. These beneficial effects are maintained for a minimum of 8 consecutive weeks of treatment. With minimal absorption and low systemic bioavailability, elobixibat is generally well tolerated and may offer the added benefit of improving serum lipid profiles through bile acid depletion.

Prucalopride in the treatment of chronic constipation in patients from the Asia-Pacific region: a randomized, double-blind, placebo-controlled study

BACKGROUND

The study evaluated efficacy and safety of the 2 mg dose of prucalopride compared to placebo in patients with chronic constipation (CC) from the Asia-Pacific region.

METHODS

Randomized, placebo-controlled, parallel-group, phase III study with 2-week run-in, 12-week treatment phase, and 1-week follow-up. Adult patients with CC (≤2 spontaneous bowel movements per week) received 2 mg prucalopride or placebo, once-daily, for 12 weeks. Primary efficacy measure was percentage of patients with average of ≥3 spontaneous complete bowel movements (SCBMs) per week (Responders) during the 12-week treatment. A key secondary endpoint was Responders during first 4 weeks of treatment. Other efficacy assessments were based on patient diaries, their assessments of symptoms and quality of life, and investigator's assessment on efficacy of treatment. Safety assessments included adverse events, laboratory values, and cardiovascular events.

KEY RESULTS

Efficacy and safety were evaluated for 501 patients who received study drug. On the primary endpoint, prucalopride was significantly more effective than placebo with 83 (33.3%) vs 26 (10.3%) patients having a weekly average of ≥3 SCBMs during the 12-week treatment (P < 0.001). Respective percentages were 34.5%vs 11.1% over first 4 weeks (P < 0.001). On other secondary endpoints, clinical improvement was generally larger and statistically superior (P < 0.001) in the prucalopride group. Most frequently reported adverse events were diarrhea, nausea, abdominal pain, and headache.

CONCLUSION & INFERENCES

Prucalopride 2 mg given once-daily significantly improved bowel function, associated symptoms, and satisfaction in CC over a 12-week treatment period, and was safe and well tolerated by patients in the Asia-Pacific region.

Assessment of the cardiac safety of prucalopride in healthy volunteers: a randomized, double-blind, placebo- and positive-controlled thorough QT study

AIMS

To assess steady-state effects of therapeutic and supra-therapeutic doses of prucalopride on the QT interval using a novel design involving a parallel placebo group with nested crossover for positive control.

METHODS

A double-blind, double-dummy, placebo- and active-controlled study was conducted in 120 healthy male and female volunteers (NCT00903747). Volunteers were randomized to receive prucalopride 2-10 mg once daily (therapeutic and supratherapeutic doses, respectively) (group 1), placebo with 400 mg moxifloxacin on day 1 (group 2a), or placebo with moxifloxacin on day 15 (group 2b). Twelve-lead 24 h Holter ECGs recorded at various time-points were evaluated blind and centrally.

RESULTS

Estimated mean difference in study specific corrected QT interval (QT(c)SS) time-matched change from baseline between prucalopride (2 and 10 mg) and placebo was <5 ms at all time points (maximum mean difference: 3.83 ms at 3.5 h post dose on day 5 with 2 mg [90% Cl -0.33, 6.38 ms]). Upper limits of the two-sided 90% CI for QT(c)SS were all <10 ms. There were no outlying QT(c)SS values >450 ms and no subjects had an increase >60 ms following prucalopride. Moxifloxacin produced the expected significant changes in QT(c)SS (>5 ms, maximum of +12.7 ms at 5 h post dose) at all time-points except 1 h post dose. Prucalopride resulted in small increases in heart rate (maximum of 5.8 beats min(-1)), which were similar for 2 and 10 mg. Prucalopride was well tolerated after first day of treatment.

CONCLUSION

Prucalopride at both therapeutic and supra therapeutic doses has no clinically significant effects on cardiac repolarisation in healthy volunteers.

Assessment of the cardiac safety of prucalopride in healthy volunteers: a randomized, double-blind, placebo- and positive-controlled thorough QT study

AIMS

To assess steady-state effects of therapeutic and supra-therapeutic doses of prucalopride on the QT interval using a novel design involving a parallel placebo group with nested crossover for positive control.

METHODS

A double-blind, double-dummy, placebo- and active-controlled study was conducted in 120 healthy male and female volunteers (NCT00903747). Volunteers were randomized to receive prucalopride 2-10 mg once daily (therapeutic and supratherapeutic doses, respectively) (group 1), placebo with 400 mg moxifloxacin on day 1 (group 2a), or placebo with moxifloxacin on day 15 (group 2b). Twelve-lead 24 h Holter ECGs recorded at various time-points were evaluated blind and centrally.

RESULTS

Estimated mean difference in study specific corrected QT interval (QT(c)SS) time-matched change from baseline between prucalopride (2 and 10 mg) and placebo was <5 ms at all time points (maximum mean difference: 3.83 ms at 3.5 h post dose on day 5 with 2 mg [90% Cl -0.33, 6.38 ms]). Upper limits of the two-sided 90% CI for QT(c)SS were all <10 ms. There were no outlying QT(c)SS values >450 ms and no subjects had an increase >60 ms following prucalopride. Moxifloxacin produced the expected significant changes in QT(c)SS (>5 ms, maximum of +12.7 ms at 5 h post dose) at all time-points except 1 h post dose. Prucalopride resulted in small increases in heart rate (maximum of 5.8 beats min(-1)), which were similar for 2 and 10 mg. Prucalopride was well tolerated after first day of treatment.

CONCLUSION

Prucalopride at both therapeutic and supra therapeutic doses has no clinically significant effects on cardiac repolarisation in healthy volunteers.

Brain-gut axis: from basic understanding to treatment of IBS and related disorders

The present review describes advances in understanding the mechanisms and provide an update of present and promising therapy directed at the gut or the brain in the treatment of irritable bowel syndrome (IBS). The diagnosis of IBS typically is based on identification of symptoms, such as the Rome III criteria for IBS in adults and children. The criteria are similar in children and adults. The focus of the present review is the bowel dysfunction associated with IBS.

Prucalopride: safety, efficacy and potential applications

Chronic constipation is a very common functional gastrointestinal disorder which can be associated with significant impairments in quality of life for some people with the condition. Its management has, traditionally, been based on dietary and lifestyle changes and the use of a variety of laxative agents. The evidence base for the efficacy of the latter is, in many cases, slim. Not surprisingly, many patients remain dissatisfied with laxatives thus leading to the development of more pharmacological approaches. Among these approaches is the use of prokinetic agents; while prior molecules have been troubled by lack of selectivity and cardiac side effects, the new agent, prucalopride, appears to be highly selective for the serotonin 5-HT4 receptor and is, therefore, a potent stimulator of gut motility. In three large pivotal randomized controlled trials, prucalopride has been effective in relieving the cardinal symptoms of chronic constipation; these effects have been sustained in open-label follow up for as long as 18 months. The safety profile has been encouraging and, especially so, the absence of arrhythmogenic potential. Studies in men, in constipation-predominant irritable bowel syndrome and in other motor disorders are eagerly awaited.

Targeting ion channels for the treatment of gastrointestinal motility disorders

Gastrointestinal (GI) functional and motility disorders are highly prevalent and responsible for long-term morbidity and sometimes mortality in the affected patients. It is estimated that one in three persons has a GI functional or motility disorder. However, diagnosis and treatment of these widespread conditions remains challenging. This partly stems from the multisystem pathophysiology, including processing abnormalities in the central and peripheral (enteric) nervous systems and motor dysfunction in the GI wall. Interstitial cells of Cajal (ICCs) are central to the generation and propagation of the cyclical electrical activity and smooth muscle cells (SMCs) are responsible for electromechanical coupling. In these and other excitable cells voltage-sensitive ion channels (VSICs) are the main molecular units that generate and regulate electrical activity. Thus, VSICs are potential targets for intervention in GI motility disorders. Research in this area has flourished with advances in the experimental methods in molecular and structural biology and electrophysiology. However, our understanding of the molecular mechanisms responsible for the complex and variable electrical behavior of ICCs and SMCs remains incomplete. In this review, we focus on the slow waves and action potentials in ICCs and SMCs. We describe the constituent VSICs, which include voltage-gated sodium (Na(V)), calcium (Ca(V)), potassium (K(V), K(Ca)), chloride (Cl(-)) and nonselective ion channels (transient receptor potentials [TRPs]). VSICs have significant structural homology and common functional mechanisms. We outline the approaches and limitations and provide examples of targeting VSICs at the pores, voltage sensors and alternatively spliced sites. Rational drug design can come from an integrated view of the structure and mechanisms of gating and activation by voltage or mechanical stress.

Evolving concepts in chronic constipation in Europe and elsewhere: not worlds apart

Chronic constipation (CC) is widely prevalent in the Western world, with a significant negative impact on quality of life, yet new and effective pharmacological and non-pharmacological treatment options have only recently emerged. The article by Tack and colleagues in the current issue of NGM is timely with the recent introduction of the serotonin type 4 receptor agonist prucalopride in Europe and wider acceptance of anorectal biofeedback for patients with pelvic floor dyssynergia. This Editorial (i) highlights the importance of identifying patients with pelvic floor dysfunction who are candidates for pelvic floor retraining programs and (ii) discusses the potential limitations of the 5-HT4 agonist, prucalopride, as an early option in the treatment algorithm for CC.

Diagnosis and treatment of chronic constipation--a European perspective

BACKGROUND

Although constipation can be a chronic and severe problem, it is largely treated empirically. Evidence for the efficacy of some of the older laxatives from well-designed trials is limited. Patients often report high levels of dissatisfaction with their treatment, which is attributed to a lack of efficacy or unpleasant side-effects. Management guidelines and recommendations are limited and are not sufficiently current to include treatments that became available more recently, such as prokinetic agents in Europe.

PURPOSE

We present an overview of the pathophysiology, diagnosis, current management and available guidelines for the treatment of chronic constipation, and include recent data on the efficacy and potential clinical use of the more newly available therapeutic agents. Based on published algorithms and guidelines on the management of chronic constipation, secondary pathologies and causes are first excluded and then diet, lifestyle, and, if available, behavioral measures adopted. If these fail, bulk-forming, osmotic, and stimulant laxatives can be used. If symptoms are not satisfactorily resolved, a prokinetic agent such as prucalopride can be prescribed. Biofeedback is recommended as a treatment for chronic constipation in patients with disordered defecation. Surgery should only be considered once all other treatment options have been exhausted.

[Guidelines for the treatment of constipation]

While constipation is a common symptom in Korea, there are no existing treatment guidelines. Although constipation may occur as a result of organic cause, there is no obstructive mucosal or structural cause in the vast majority of patients with constipation. The present paper deals with only the management of functional constipation: lifestyle changes; bulking agents and stool softeners; osmotic agents; stimulant laxatives; prokinetics; biofeedback and surgical treatments. Exercise and dietary fiber are helpful in some patients with constipation. Laxatives including bulking agents, stool softeners, osmotic agents, and stimulant laxatives have been found to be more effective than placebo at relieving symptoms of constipation. New enterokinetic agents that affect peristalsis through selective interaction with 5-hydroxytryptamine-4 receptors can be effective in patients with constipation who cannot get adequate relief from current laxatives. Biofeedback can relieve symptoms in selected patients with pelvic floor dyssynergia. Surgical treatments can be helpful in some patients with refractory constipation.

Investigational agents for the irritable bowel syndrome

IMPORTANCE OF THE FIELD

Irritable bowel syndrome (IBS) is a common disorder with significant health and economic consequences. The etiology of IBS is complex and appears to be multifactorial. Traditional IBS therapies have been directed primarily at the relief of individual symptoms but have been largely disappointing. This has triggered the search for newer treatment strategies with improved patient outcomes.

AREAS COVERED IN THIS REVIEW

Enhanced knowledge about the putative pathophysiology of IBS has allowed the identification of new mechanistic targets for treatment. Our aim is to review emerging and promising drugs in the treatment of IBS based on disease pathophysiology. Data were extracted using Medline and PubMed search engines until January 2010. Abstracts were identified through 'Web of Science' and abstract supplements of major gastrointestinal scientific meetings. Drugs were classified according to mechanism of action and those with efficacy in trials involving human subjects examined.

WHAT THE READER WILL GAIN

Additional insight into the pathophysiology as well as current and prospective treatments of IBS.

TAKE HOME MESSAGE

A multitude of putative drug targets have been identified and some novel treatments have progressed through to human clinical trials, but very few will be approved for the market in the near future. Moreover, and in keeping with the complex and multifactorial nature of this syndrome, it is unlikely that there will be one dominant and universally effective form of therapy for all IBS patients.

Current and future therapies for chronic constipation

In this article, traditional and novel therapies for chronic constipation are reviewed. Traditional laxatives are effective at inducing bowel movements, but efficacy in long-term management and efficacy on constipation-associated abdominal symptoms are less well established, with the exception of polyethylene glycol, for which long-term studies confirm sustained efficacy. Recently approved drugs include the colonic secretagogue lubiprostone and the 5-HT4 agonist prucalopride. In controlled trials in chronic constipation, these drugs were shown to significantly improve constipation and its associated symptoms, with a favourable safety record. Methylnaltrexone, a subcutaneously administered peripherally acting mu opioid receptor antagonist, has recently been approved for opioid-induced constipation in terminally ill patients. New agents under evaluation include the 5-HT4 agonists velusetrag and naronapride, the guanylate cyclase-C receptor agonist linaclotide and the peripherally acting mu opioid receptor antagonist alvimopan.

Constipation, IBs and the 5-HT4 Receptor: What Role for Prucalopride?

After the problems associated with the non-selective 5-HT4 receptor agonists cisapride and tegaserod, the 5-HT4 receptor is now beginning to come in from the cold. Thus, prucalopride is now the first of a new class of drug defined by selectivity and high intrinsic activity at the 5-HT4 receptor. Prucalopride has been developed for treatment of chronic constipation rather than constipation-predominant irritable bowel syndrome (IBS). This follows the trend of first evaluating new gastrointestinal (GI) prokinetic drugs in disorders where disrupted GI motility is known to exist, rather than in a functional bowel disorder where changes in motility are uncertain. If prucalopride is not progressed towards the IBS indication, it has at least shown the way for other selective 5-HT4 receptor agonists. Most notable among these is TD-5108 (velusetrag), also characterized by good selectivity at the 5-HT4 receptor, high intrinsic activity and efficacy in patients with chronic constipation.

Detailed knowledge of cellular expression of G protein-coupled receptors in the human enteric nervous system is essential for understanding their diverse actions

G protein-coupled receptors (GPCRs) comprise a large and diverse superfamily of transmembrane receptors that mediate the functions of an extraordinarily large number of extracellular ligands. They control many major physiological processes and are involved in diverse pathological processes, including gastrointestinal diseases. G protein-coupled receptors are one of the most targeted classes in pharmaceutical drug research. At present, much of our knowledge concerning the expression, distribution and function of GPCRs in the gut has been gleaned from studies performed in experimental models. Data obtained in the human digestive tract, especially in the enteric nervous system, are sparse and incomplete, although enteric neurons have a key position in almost all physiological and pathophysiological processes in the gut. Knowledge of cellular distribution of GPCRs, of regional differences in GPCR expression, and of altered GPCR expression during pathophysiological conditions in the human gut, will lead to a better understanding of GPCR activity, but will also contribute to the development of new drugs. In the current issue of the Journal, Harrington et al. describe the presence and cellular localization of muscarinic receptors in the human colon. Morphologically, orientated studies on the cellular expression of GPCRs in the human gut have to be encouraged, because these studies will yield data that are of therapeutic relevance.

Challenges and prospects for pharmacotherapy in functional gastrointestinal disorders

Functional gastrointestinal disorders, such as irritable bowel syndrome and functional dyspepsia, are complex conditions with multiple factors contributing to their pathophysiology. As a consequence they are difficult to treat and have posed significant challenges to the pharmaceutical industry when trying to develop new and effective treatments. This review provides an overview of these difficulties and how the industry is reshaping its drug developmental strategies. It describes some of the more significant and encouraging advances that have occurred, and discusses how future research might embrace the opportunities provided by advances in genetic and in particular, epigenetic research.

Update on the management of constipation in the elderly: new treatment options

Constipation disproportionately affects older adults, with a prevalences of 50% in community-dwelling elderly and 74% in nursing-home residents. Loss of mobility, medications, underlying diseases, impaired anorectal sensation, and ignoring calls to defecate are as important as dyssynergic defecation or irritable bowel syndrome in causing constipation. Detailed medical history on medications and co-morbid problems, and meticulous digital rectal examination may help identify causes of constipation. Likewise, blood tests and colonoscopy may identify organic causes such as colon cancer. Physiological tests such as colonic transit study with radio-opaque markers or wireless motility capsule, anorectal manometry, and balloon expulsion tests can identify disorders of colonic and anorectal function. However, in the elderly, there is usually more than one mechanism, requiring an individualized but multifactorial treatment approach. The management of constipation continues to evolve. Although osmotic laxatives such as polyethylene glycol remain mainstay, several new agents that target different mechanisms appear promising such as chloride-channel activator (lubiprostone), guanylate cyclase agonist (linaclotide), 5HT₄ agonist (prucalopride), and peripherally acting μ-opioid receptor antagonists (alvimopan and methylnaltrexone) for opioid-induced constipation. Biofeedback therapy is efficacious for treating dyssynergic defecation and fecal impaction with soiling. However, data on efficacy and safety of drugs in elderly are limited and urgently needed.

New-generation 5-HT4 receptor agonists: potential for treatment of gastrointestinal motility disorders

IMPORTANCE OF THE FIELD

Gastrointestinal (GI) dysmotility is an important mechanism in functional GI disorders (FGIDs) including constipation, irritable bowel syndrome, functional dyspepsia, and gastroparesis. 5-hydroxytryptamine(4) (5-HT(4)) receptors are targets for the treatment of GI motility disorders. However, older 5-HT(4) receptor agonists had limited clinical success because they were associated with changes in the function of the cardiac HERG potassium channel.

AREAS COVERED IN THIS REVIEW

We conducted a PubMed search using the following key words alone or in combination: 5-HT(4), safety, toxicity, pharmacokinetics, pharmacodynamics, clinical trial, cardiac, hERG, arrhythmia, potassium current, elderly, prucalopride, ATI-7505, and velusetrag (TD-5108), to review mechanisms of action, clinical efficacy, safety and tolerability of three new-generation 5-HT(4) receptor agonists.

WHAT THE READER WILL GAIN

Prucalopride, ATI-7505, and velusetrag (TD-5108) are highly selective, high-affinity 5-HT(4) receptor agonists that are devoid of action on other receptors within their therapeutic range. Their efficacy has been demonstrated in pharmacodynamic studies which demonstrate acceleration of colonic transit and, to a variable degree, in clinical trials that significantly relieve chronic constipation. Currently available evidence shows that the new 5-HT(4) receptor agonists have safe cardiac profiles.

TAKE HOME MESSAGE

New-generation 5-HT(4) receptor agonists and future drugs targeting organ-specific splice variants are promising approaches to treat GI dysmotility, particularly colonic diseases.

Role of prucalopride, a serotonin (5-HT(4)) receptor agonist, for the treatment of chronic constipation

Constipation affects up to a quarter of the population in developed countries and is associated with poor quality of life and significant economic burden. Many patients with chronic constipation are dissatisfied with current therapy due to lack of long-term efficacy or side effects. Previous nonselective 5-hydroxytryptamine receptor 4 (5-HT₄) agonists have been associated with significant interactions with other receptors (5-HT_1B, 5-HT_1D, and 5-HT_2B for tegaserod; hERG for cisapride), leading to adverse cardiovascular events resulting in withdrawal of these drugs from the market. Prucalopride is a novel gastrointestinal prokinetic agent. It acts as a high affinity, highly-selective 5-HT₄ agonist. Its efficacy in patients with chronic constipation has been demonstrated in several phase II and phase III clinical trials showing significant improvements in bowel transit, bowel function, gastrointestinal symptoms, and quality of life, with benefit maintained for up to 24 months in open label, multicenter, follow-up studies. Prucalopride’s high selectivity for the 5-HT₄ receptor may explain its favorable safety and tolerability profiles, even in elderly subjects with stable cardiovascular disease. Prucalopride is a well tolerated and efficacious prokinetic medication that should enhance the treatment of chronic constipation unresponsive to first-line treatments.

Prucalopride

Prucalopride, a first-in-class dihydrobenzofuran-carboxamide derivative, is a potent, selective and specific serotonin 5-HT(4) receptor agonist with enterokinetic properties. Over a 12-week treatment period, prucalopride 2 and 4 mg once daily significantly improved bowel habit assessments (based on patient diary data) relative to placebo in three large, randomized, double-blind, multicentre trials in patients (aged 17-95 years) with severe chronic constipation, the majority of whom were women who experienced inadequate relief with previous therapies. There was no additional benefit with the 4 mg/day over the 2 mg/day dosage of prucalopride. Patient assessments of constipation symptoms and severity, treatment efficacy, satisfaction with bowel habit and treatment, and health-related quality of life were also significantly improved with prucalopride compared with placebo. The improvement in patient satisfaction with bowel habit and treatment was maintained for up to 24 months in open-label, multicentre, long-term follow-up studies. Prucalopride therapy was generally well tolerated; most adverse events in the 12-week studies were transient and of mild to moderate severity. In terms of cardiovascular tolerability, the incidence of QT interval prolongation with prucalopride at dosages of 2 and 4 mg/day was low and similar to that with placebo. Moreover, prucalopride at dosages up to 20 mg/day (10-fold higher than the recommended therapeutic dosage) had no clinically relevant effects on cardiovascular parameters in healthy volunteers.

Psychometric performance and clinical meaningfulness of the Patient Assessment of Constipation-Quality of Life questionnaire in prucalopride (RESOLOR) trials for chronic constipation

BACKGROUND

The Patient Assessment of Constipation-Quality of Life (PAC-QOL) is a self-reported questionnaire measuring health-related quality of life (HRQL) of constipated patients and was used as secondary endpoint in three identical double-blind, randomized, placebo-controlled Phase III clinical trials. These 12-week trials in subjects with severe chronic constipation evaluated the effects of prucalopride, a selective 5-HT(4) agonist given orally once daily.

METHODS

To consolidate the main treatment effect results observed in the prucalopride trial populations, analyses were undertaken on the pooled data of the three trials to confirm the psychometric properties of the PAC-QOL and to provide guidance for the interpretation of the clinical significance of its scores.

KEY RESULTS

The evaluation of the psychometric properties confirmed the PAC-QOL reliability, validity and responsiveness to measure the impact of chronic constipation symptoms on HRQL in the prucalopride trials. The 1-point improvement in PAC-QOL scores used as target response level for the main treatment effect analyses was validated as a relevant definition of response for treatment group comparisons. Cumulative distribution curves, drawn for each treatment group to provide more complete information on treatment effects than single minimal important difference point estimates, demonstrated consistent superior effects of prucalopride over placebo on all PAC-QOL scores.

CONCLUSIONS & INFERENCES

The PAC-QOL questionnaire is a useful measurement tool to assess, from a patient perspective, the potential therapeutic value of chronic constipation treatments in clinical trials and, by directly reflecting the patient's own perspective on constipation and its treatment, eventually also for informing daily medical practice.

Translating 5-HT receptor pharmacology

Since metoclopramide was first described (in 1964) there have been several attempts to develop compounds which retained gastrointestinal prokinetic activity (via 5-HT(4) receptor activation) but without the limiting side effects associated with dopamine D(2) receptor antagonism. Early compounds (mosapride, cisapride, renzapride, tegaserod) were identified before several of the 5-HT receptors were even described (including 5-HT(4) and 5-HT(2B)), whereas prucalopride came later. Several compounds were hampered by non-selectivity, introducing cardiac liability (cisapride: activity at human Ether-a-go-go Related Gene) or potentially, a reduced intestinal prokinetic activity caused by activity at a second 5-HT receptor (renzapride: antagonism at the 5-HT(3) receptor; tegaserod: antagonism at the 5-HT(2B) receptor). Poor intrinsic activity at gastrointestinal 5-HT(4) receptors has also been an issue (mosapride, tegaserod). Perhaps prucalopride has now achieved the profile of good selectivity of action and high intrinsic activity at intestinal 5-HT(4) receptors, without clinically-meaningful actions on 5-HT(4) receptors in the heart. The progress of this compound for treatment of chronic constipation, as well as competitor molecules such as ATI-7505 and TD-5108, will now be followed with interest as each attempts to differentiate themselves from each other. Perhaps at last, 5-HT(4) receptor agonists are being given the chance to show what they can do.

Translating 5-HT receptor pharmacology

Since metoclopramide was first described (in 1964) there have been several attempts to develop compounds which retained gastrointestinal prokinetic activity (via 5-HT(4) receptor activation) but without the limiting side effects associated with dopamine D(2) receptor antagonism. Early compounds (mosapride, cisapride, renzapride, tegaserod) were identified before several of the 5-HT receptors were even described (including 5-HT(4) and 5-HT(2B)), whereas prucalopride came later. Several compounds were hampered by non-selectivity, introducing cardiac liability (cisapride: activity at human Ether-a-go-go Related Gene) or potentially, a reduced intestinal prokinetic activity caused by activity at a second 5-HT receptor (renzapride: antagonism at the 5-HT(3) receptor; tegaserod: antagonism at the 5-HT(2B) receptor). Poor intrinsic activity at gastrointestinal 5-HT(4) receptors has also been an issue (mosapride, tegaserod). Perhaps prucalopride has now achieved the profile of good selectivity of action and high intrinsic activity at intestinal 5-HT(4) receptors, without clinically-meaningful actions on 5-HT(4) receptors in the heart. The progress of this compound for treatment of chronic constipation, as well as competitor molecules such as ATI-7505 and TD-5108, will now be followed with interest as each attempts to differentiate themselves from each other. Perhaps at last, 5-HT(4) receptor agonists are being given the chance to show what they can do.