First pharmacokinetic-pharmacodynamic study in humans with a selective 5-hydroxytryptamine4 receptor agonist

Tegaserod: What's Old Is New Again

Irritable bowel syndrome with constipation (IBS-C) and chronic idiopathic constipation (CIC) are common gastrointestinal disorders imposing considerable impact on the quality of life and well-being of affected individuals. A paucity of evidence-based treatment options exist for CIC and IBS-C sufferers. Tegaserod, a 5-HT₄ agonist, has a substantial body of preclinical and clinical study evidence to support its beneficial role in modulating sensorimotor function of the luminal gastrointestinal tract. Tegaserod was first approved for use by the U.S. Food and Drug Administration for the management of IBS-C and CIC in 2002 and 2004, respectively. Tegaserod enjoyed a successful uptake in the management of these disorders during its first several years of availability in the United States, but was later withdrawn from the market in 2007 over concerns related to adverse cardiovascular events. Since then, additional safety data has been generated, and following a resubmission and review by the Food and Drug Administration, in April 2019, tegaserod was once again approved for use in IBS-C under a more restricted labeling, confining use to women under 65 years of age without heart disease or additional cardiovascular risk factors. This review summarizes the regulatory journey of tegaserod and details the existing pharmacokinetic, physiologic, clinical, and safety data of tegaserod generated over the last 2 decades. The discussion also examines the future of tegaserod in the treatment of these constipation disorders, as well as its potential role in other related disorders of brain-gut interaction.

Active Targeted Nanoemulsions for Repurposing of Tegaserod in Alzheimer's Disease Treatment

Background and Purpose: The activation of 5-HT₄ receptors with agonists has emerged as a valuable therapeutic strategy to treat Alzheimer’s disease (AD) by enhancing the nonamyloidogenic pathway. Here, the potential therapeutic effects of tegaserod, an effective agent for irritable bowel syndrome, were assessed for AD treatment. To envisage its efficient repurposing, tegaserod-loaded nanoemulsions were developed and functionalized by a blood–brain barrier shuttle peptide. Results: The butyrylcholinesterase inhibitory activity of tegaserod and its neuroprotective cellular effects were highlighted, confirming the interest of this pleiotropic drug for AD treatment. In regard to its drugability profile, and in order to limit its peripheral distribution after IV administration, its encapsulation into monodisperse lipid nanoemulsions (Tg-NEs) of about 50 nm, and with neutral zeta potential characteristics, was performed. The stability of the formulation in stock conditions at 4 °C and in blood biomimetic medium was established. The adsorption on Tg-NEs of peptide-22 was realized. The functionalized NEs were characterized by chromatographic methods (SEC and C₁₈/HPLC) and isothermal titration calorimetry, attesting the efficiency of the adsorption. From in vitro assays, these nanocarriers appeared suitable for enabling tegaserod controlled release without hemolytic properties. Conclusion: The developed peptide-22 functionalized Tg-NEs appear as a valuable tool to allow exploration of the repurposed tegaserod in AD treatment in further preclinical studies.

Tegaserod for the Treatment of Irritable Bowel Syndrome

Background: Tegaserod (Zelnorm®) is a 5-hydroxytryptamine (serotonin) type 4 receptor agonist for the treatment of hypomotility disorders of the lower gastrointestinal tract associated with the irritable bowel syndrome with constipation (IBS-C).

Objective: The authors provide the reader with a better understanding on tegaserod mechanism of action, on its pharmacodynamics and pharmacokinetic properties, on safety and tolerability, with a summary of the key published clinical trials conducted in patients with irritable bowel syndrome (IBS). Its effects on colon inflammation have also been described.

Results: Tegaserod was withdrawn in 2007 due to increased risks of cardiovascular adverse effects. The manufacturer denied this, because pre-existing cardiovascular disease or risk factors were attributed to all affected patients. Thus, no causal relationship between tegaserod use and cardiovascular events was clearly shown. A matched case-control study of tegaserod-treated with untreated patients found no association between tegaserod and adverse cardiovascular outcomes. Despite its adverse effects, tegaserod resulted to be effective in treating chronic constipation in adult women aged < 65 years with IBS-C, while the safety and effectiveness of tegaserod in men with IBS-C have not been established.

Conclusion: Tegaserod was resubmitted to the Food and Drug Administration in 2018 for use in a low-risk population. Moreover, tegaserod has also been shown to improve symptoms, enhance gastric accommodation and significantly attenuate visceral pain arising from the colon in functional dyspepsia patients. Treatment with tegaserod seems also to exert a protective effect in inflamed colons, reducing the severity of colitis in animal models.

Cardiovascular safety of prokinetic agents: A focus on drug-induced arrhythmias

BACKGROUND

Gastrointestinal sensorimotor dysfunction underlies a wide range of esophageal, gastric, and intestinal motility and functional disorders that collectively constitute nearly half of all referrals to gastroenterologists. As a result, substantial effort has been dedicated toward the development of prokinetic agents intended to augment or restore normal gastrointestinal motility. However, the use of several clinically efficacious gastroprokinetic agents, such as cisapride, domperidone, erythromycin, and tegaserod, is associated with unfavorable cardiovascular safety profiles, leading to restrictions in their use.

PURPOSE

The purpose of this review is to detail the cellular and molecular mechanisms that lead commonly to drug-induced cardiac arrhythmias, specifically drug-induced long QT syndrome, torsades de pointes, and ventricular fibrillation, to examine the cardiovascular safety profiles of several classes of prokinetic agents currently in clinical use, and to explore potential strategies by which the risk of drug-induced cardiac arrhythmia associated with prokinetic agents and other QT interval prolonging medications can be mitigated successfully.

The use of biomarkers in human pharmacology (Phase I) studies

The development of a new medicine is a risky and costly undertaking that requires careful planning. This planning is largely applied to the operational aspects of the development and less so to the scientific objectives and methodology. The drugs that will be developed in the future will increasingly affect pathophysiological pathways that have been largely unexplored. Such drug prototypes cannot be immediately introduced in large clinical trials. The effects of the drug on normal physiology, pathophysiology, and eventually the desired clinical effects will need to be evaluated in a structured approach, based on the definition of drug development as providing answers to important questions by appropriate clinical studies. This review describes the selection process for biomarkers that are fit-for-purpose for the stage of drug development in which they are used. This structured and practical approach is widely applicable and particularly useful for the early stages of innovative drug development.

Effect of the 5-HT4 receptor and serotonin transporter on visceral hypersensitivity in rats

Visceral hypersensitivity plays an important role in motor and sensory abnormalities associated with irritable bowel syndrome, but the underlying mechanisms are not fully understood. The present study was designed to evaluate the expression of the 5-HT₄ receptor and the serotonin transporter (SERT) as well as their roles in chronic visceral hypersensitivity using a rat model. Neonatal male Sprague-Dawley rats received intracolonic injections of 0.5% acetic acid (0.3-0.5 mL at different times) between postnatal days 8 and 21 to establish an animal model of visceral hypersensitivity. On day 43, the threshold intensity for a visually identifiable contraction of the abdominal wall and body arching were recorded during rectal distention. Histological evaluation and the myeloperoxidase activity assay were performed to determine the severity of inflammation. The 5-HT₄ receptor and SERT expression of the ascending colon were monitored using immunohistochemistry and Western blot analyses; the plasma 5-HT levels were measured using an ELISA method. As expected, transient colonic irritation at the neonatal stage led to visceral hypersensitivity, but no mucosal inflammation was later detected during adulthood. Using this model, we found reduced SERT expression (0.298 ± 0.038 vs 0.634 ± 0.200, P < 0.05) and increased 5-HT₄ receptor expression (0.308 ± 0.017 vs 0.298 ± 0.021, P < 0.05). Treatment with fluoxetine (10 mg·kg⁻¹·day⁻¹, days 36-42), tegaserod (1 mg·kg⁻¹·day⁻¹, day 43), or the combination of both, reduced visceral hypersensitivity and plasma 5-HT levels. Fluoxetine treatment increased 5-HT₄ receptor expression (0.322 ± 0.020 vs 0.308 ± 0.017, P < 0.01) but not SERT expression (0.219 ± 0.039 vs 0.298 ± 0.038, P = 0.654). These results indicate that both the 5-HT₄ receptor and SERT play a role in the pathogenesis of visceral hypersensitivity, and its mechanism may be involved in the local 5-HT level.

Network neighbors of drug targets contribute to drug side-effect similarity

In pharmacology, it is essential to identify the molecular mechanisms of drug action in order to understand adverse side effects. These adverse side effects have been used to infer whether two drugs share a target protein. However, side-effect similarity of drugs could also be caused by their target proteins being close in a molecular network, which as such could cause similar downstream effects. In this study, we investigated the proportion of side-effect similarities that is due to targets that are close in the network compared to shared drug targets. We found that only a minor fraction of side-effect similarities (5.8 %) are caused by drugs targeting proteins close in the network, compared to side-effect similarities caused by overlapping drug targets (64%). Moreover, these targets that cause similar side effects are more often in a linear part of the network, having two or less interactions, than drug targets in general. Based on the examples, we gained novel insight into the molecular mechanisms of side effects associated with several drug targets. Looking forward, such analyses will be extremely useful in the process of drug development to better understand adverse side effects.

Developing drug prototypes: pharmacology replaces safety and tolerability?

New medicines are designed to bind to receptors or enzymes and are tested in animal cells, tissues and whole organisms in a highly scientific process. Subsequently they are often administered to human subjects with tolerability as the primary objective. The process of development is considered to be linear and consecutive and passes through the famous four phases of development (Phase I-Phase IV). This is efficient for those projects for which the uncertainty about the development is low. There is, however, an increasing number of new prototypical compounds resulting from the increased biological knowledge with a high level of uncertainty. For these prototypical drugs development has to proceed in a much more adaptive manner, using tailor-made objectives, the development of special methodology and a cyclical rather than a linear type of project management.

Development and evaluation of a pH-dependent sustained release tablet for irritable bowel syndrome

The overall objective of this study was to develop a pH-dependent sustained release tablet formulation of a model drug, tegaserod maleate (TM), which is a poorly water soluble and acid labile drug in gastric milieu. The formulation's goal was to allow the dosage form to pass through the stomach intact, start disintegrating in the upper small intestine and slowly release the active in a controlled manner. Partition coefficient, contact angle and drug-excipient compatibility were investigated as part of the preformulation studies. A pH-dependent sustained release tablet was prepared using a combination of Eudragit L100 and Eudragit S100. The effects of solubilizer, disintegrant, binder, coating polymer concentration, pore former, and plasticizer on the drug release rate were determined. The results demonstrated that approximately 90% of the drug was released in a sustained release manner in the pH 6.8 phosphate buffer within 12 h while no drug was detected when subjected to drug release studies in 0.1 mol/L hydrochloric acid for 2 h. The drug release mechanism involved stress points and/or pore formation in the coated film. The coated tablets were stable at 40 degrees C/75% RH for 3 months. These results highlighted the feasibility of this coated tablet system containing TM, which may contribute to the successful treatment of irritable bowel syndrome.

Effect of tegaserod on colonic transit time in male patients with constipation-predominant irritable bowel syndrome

BACKGROUND AND AIMS

Tegaserod is approved for the treatment of constipation-predominant irritable bowel syndrome (C-IBS) in females. The aim of this study was to evaluate the effect of tegaserod on colonic transit time (CTT) and symptoms in male patients with C-IBS.

METHODS

Forty-four males with C-IBS (Rome II) were enrolled. After a baseline washout period of 2 weeks, 40 patients were randomized to 6 mg twice daily of tegaserod or placebo for 12 weeks. Daily bowel habits and weekly satisfactory relief of symptoms were recorded. Total and segmental CTT were measured using radiopaque markers at baseline and after treatment.

RESULTS

The mean +/- SD for the total colonic, right colonic, left colonic and rectosigmoid transit time (in hours) were 18.96 +/- 3.92, 7.74 +/- 1.55, 5.64 +/- 1.51 and 5.58 +/- 2.2 in the tegaserod group compared to 22.47 +/- 3.73, 9.69 +/- 2.33, 6.6 +/- 1.32 and 6.18 +/- 2.22 in the placebo group at the end of 12 weeks. There was a statistically significant difference in the total, right and left CTT in the tegaserod group (P < 0.05) at the end of treatment. Global satisfactory relief at the end of 12 weeks was 75% in the tegaserod group and 50% in the placebo group (P > 0.05). Greater stool frequency occurred in the tegaserod group (P > 0.05). There was a significant decrease in the stool consistency at the end of 12 weeks in patients treated with tegaserod (P < 0.05).

CONCLUSIONS

Tegaserod causes significant acceleration of CTT in male patients with C-IBS. Although there was a trend towards improvement in bowel symptoms in the treated group, this effect was not statistically significant.

Tegaserod for constipation-predominant irritable bowel syndrome

Tegaserod, a selective and partial agonist at the 5-hydroxytryptamine (5-HT [serotonin]) receptor subtype 4 (5-HT4), is the only United States Food and Drug Administration-approved drug for the treatment of constipation-predominant irritable bowel syndrome (IBS) in women. The drug's stimulation of 5-HT4 receptors on intestinal enterocytes increases peristaltic activity and fluid secretion into the gut lumen, facilitating stool passage. In addition, affinity of tegaserod for 5-HT4 receptors modulates visceral sensitivity, which helps alleviate abdominal pain associated with constipation-predominant IBS. The drug's pharmacokinetic and pharmacodynamic parameters do not differ significantly with age or sex. Tegaserod safely and effectively relieves overall gastrointestinal symptoms and abdominal discomfort and normalizes bowel habits in patients with constipation-predominant IBS. It is associated with few drug interactions. In clinical studies, tegaserod was well tolerated, and its adverse-effect profile was similar to that of placebo. Severe diarrhea, as well as abdominal pain, flatulence, headache, and nausea, were the most commonly reported events. Patients who experience severe diarrhea should discontinue the drug. With the data available, tegaserod remains an option for patients with constipation-predominant IBS.

5-Hydroxytryptophan activates colonic myenteric neurons and propulsive motor function through 5-HT4 receptors in conscious mice

Serotonin [5-hydroxytryptamine (5-HT)] acts as a modulator of colonic motility and secretion. We characterized the action of the 5-HT precursor 5-hydroxytryptophan (5-HTP) on colonic myenteric neurons and propulsive motor activity in conscious mice. Fos immunoreactivity (IR), used as a marker of neuronal activation, was monitored in longitudinal muscle/myenteric plexus whole mount preparations of the distal colon 90 min after an intraperitoneal injection of 5-HTP. Double staining of Fos IR with peripheral choline acetyltransferase (pChAT) IR or NADPH-diaphorase activity was performed. The injection of 5-HTP (0.5, 1, 5, or 10 mg/kg ip) increased fecal pellet output and fluid content in a dose-related manner, with a peak response observed within the first 15 min postinjection. 5-HTP (0.5-10 mg/kg) dose dependently increased Fos expression in myenteric neurons, with a maximal response of 9.9 +/- 1.0 cells/ganglion [P < 0.05 vs. vehicle-treated mice (2.3 +/- 0.6 cells/ganglion)]. There was a positive correlation between Fos expression and fecal output. Of Fos-positive ganglionic cells, 40 +/- 4% were also pChAT positive and 21 +/- 5% were NADPH-diaphorase positive in response to 5-HTP, respectively. 5-HTP-induced defecation and Fos expression were completely prevented by pretreatment with the selective 5-HT4 antagonist RS-39604. These results show that 5-HTP injected peripherally increases Fos expression in different populations of cholinergic and nitrergic myenteric neurons in the distal colon and stimulates propulsive colonic motor function through 5-HT4 receptors in conscious mice. These findings suggest an important role of activation of colonic myenteric neurons in the 5-HT4 receptor-mediated colonic propulsive motor response.

Tegaserod in the treatment of irritable bowel syndrome with constipation

Tegaserod, a novel serotonin receptor agonist, has gained acceptance and widespread use for the treatment of women with irritable bowel syndrome and constipation. Development of this therapy evolved from the emerging role of serotonin in gastrointestinal motor, secretory and sensory functions. The efficacy and safety of tegaserod has been well established in women suffering from irritable bowel syndrome with constipation. Large, randomized, double-blind, placebo-controlled trials involving more than 3500 predominantly female patients with irritable bowel syndrome and constipation have demonstrated the superiority of tegaserod over placebo in improving global and individual symptoms. The most common side effects of tegaserod in clinical trials were diarrhea and headache. Recent data suggest that retreatment with tegaserod after a drug holiday is efficacious, opening the door to the possibility of intermittent therapy for patients with irritable bowel syndrome and constipation. Areas in need of further investigation include the role of tegaserod in the treatment of pain and bloating in irritable bowel syndrome, whether tegaserod has a role in male patients, the long-term efficacy of tegaserod, whether tolerance develops in a subset of patients with extended therapy and whether tegaserod is beneficial for the treatment of other functional gastrointestinal disorders.

Measurement of 5-HT4 receptor-mediated esophageal responses by digital sonomicrometry in the anesthetized rat

INTRODUCTION

In vitro studies have demonstrated a 5-HT4 receptor-mediated relaxation of the pre-contracted rat esophagus. However, it is unclear whether 5-HT4 receptor agonists affect resting esophageal tone in vivo. The activity of 5-HT and several well-established 5-HT4 receptor agonists (tegaserod, BIMU-8, cisapride, renzapride, and mosapride) was investigated in a novel in vivo model designed to measure esophageal relaxation using the technique of digital sonomicrometry.

METHODS

Miniature piezo-electric crystals were implanted externally in a longitudinal orientation on the distal esophagus of isoflurane-anesthetized, adult male Sprague-Dawley rats. Measurement of the time for transmission of ultrasonic pulses between the implanted crystals provided a continuous recording of inter-crystal distance and hence esophageal muscle length.

RESULTS

Following cumulative intravenous administration, 5-HT (1-100 microg/kg), tegaserod (1-1000 microg/kg), BIMU-8 (3-3000 microg/kg), renzapride (10-3000 microg/kg), cisapride (30-3000 microg/kg), and mosapride (30-10,000 microg/kg) produced a dose-dependent increase in esophageal inter-crystal distance. The mean ED50 values for tegaserod, BIMU-8, renzapride, cisapride, and mosapride were 11, 49, 51, 141, and 1825 microg/kg, respectively. Pre-treatment with the selective 5-HT4 receptor antagonist, piboserod (SB-207266; 1 mg/kg subcutaneously) significantly attenuated the effects of intravenous tegaserod (1-1000 microg/kg). Following cumulative intraduodenal administration (0.03-10 mg/kg), tegaserod and mosapride exhibited a dose-dependent increase in esophageal inter-crystal distance. The doses associated with a 10% increase in muscle length from the resting level were 2.6 and>10 mg/kg for tegaserod and mosapride, respectively.

DISCUSSION

In conclusion, dose-dependent, 5-HT4 receptor agonist-mediated increases in longitudinal muscle length in the rat esophagus were observed in vivo using the technique of digital sonomicrometry. This in vivo model of esophageal activity may prove useful in evaluating the activity of novel 5-HT4 receptor agonists.

Review of tegaserod in the treatment of irritable bowel syndrome

Tegaserod is a drug in a new class of compounds called aminoguanidine indoles and is structurally similar to serotonin (5-HT) with modifications that make the drug selective for the 5-HT(4) receptor. Tegaserod has a stimulatory effect on gastrointestinal (GI) motility that has been demonstrated in animal studies and in healthy adults. Tegaserod also increases GI secretion and reduces rectal sensitivity. Tegaserod is currently approved by the FDA for the treatment of women with constipation-predominant irritable bowel syndrome (C-IBS). Eight large Phase III clinical trials involving > 5000 IBS patients support the clinical efficacy of tegaserod in this group of patients. Patients who were treated with tegaserod had an overall improvement in IBS symptoms (Subject's Assessment of Global Relief) as well as in secondary end points, such as abdominal pain and discomfort, stool consistency, change in bowel movements and relief of bloating. Tegaserod was well-tolerated. The most common adverse reaction in clinical trials was diarrhoea, which was usually temporary and mild, although severe diarrhoea requiring hospitalisation has been rarely (< 1%) reported.

Safety Profile of Tegaserod, a 5-HT4 Receptor Agonist, for the Treatment of Irritable Bowel Syndrome

This article reviews the safety and tolerability profile of tegaserod, a novel selective partial agonist of the serotonin 5-HT(4) receptor. Tegaserod was recently approved for the treatment of women with irritable bowel syndrome (IBS) with constipation. Tegaserod exhibits rapid absorption from the small intestine, and is excreted unchanged in the faeces and as metabolites in the urine. Meal ingestion decreases its bioavailability. There is little effect of age or gender on pharmacokinetics, although plasma levels may be slightly higher in the elderly. Tegaserod has no effect on plasma levels of other drugs metabolised by cytochrome P450 enzyme systems. Gastrointestinal symptoms are the most common adverse effects of tegaserod therapy. In data pooled from phase III randomised controlled trials (RCTs) in IBS with constipation patients, diarrhoea was reported by 8.8% of patients treated with tegaserod 6mg twice daily versus 3.8% of patients receiving placebo. Similar rates have been observed in international post-US marketing RCTs. In most patients, tegaserod-induced diarrhoea was mild and transient. In RCTs, it did not elicit fluid or electrolyte disturbances, and fewer than 3% of IBS patients discontinued tegaserod due to diarrhoea. Since its release, rare cases of more severe diarrhoea and ischaemic colitis have been reported. The incidence of other gastrointestinal symptoms (e.g. abdominal pain, nausea, and flatulence) has been similar among tegaserod-treated patients and placebo-treated patients. Pooled analysis of phase III RCTs and post-US marketing RCTs have not demonstrated significant differences between tegaserod-treated patients and placebo-treated patients in the incidence of abdominal-pelvic surgery. There is no convincing evidence that rebound gastrointestinal symptoms occur upon termination of tegaserod therapy. Pooled analysis of phase III RCTs demonstrated an increase in the incidence of headaches among tegaserod-treated patients (6mg twice daily) compared with placebo-treated patients (15% vs 12.3%, respectively, p < 0.05), although post-US marketing RCTs have not observed this increase. Other extra-gastrointestinal adverse events occur with similar frequency among tegaserod-treated patients and placebo-treated patients. Tegaserod-treated patients in RCTs have not demonstrated significant prolongation of the QTc interval or cardiac arrhythmias compared with placebo-treated patients. Supra-therapeutic doses in healthy volunteers did not effect electrocardiographic parameters. Laboratory parameters are mostly unaffected by tegaserod, although several individuals have exhibited increased eosinophil counts. In summary, tegaserod exhibits a favourable safety and tolerability profile in IBS patients based on data from clinical trials. Diarrhoea is the most common adverse event associated with tegaserod use. Continued post-US marketing surveillance will further define the safety and tolerability profile of tegaserod.

Tegaserod: a review of its use in the management of irritable bowel syndrome with constipation in women

The treatment of irritable bowel syndrome with constipation (IBS-C) has historically been based on the severity of symptoms, with education, reassurance, dietary advice, bulking agents and laxative therapy offered as appropriate. Tegaserod (Zelnorm, Zelmac) is the first selective serotonin 5-HT(4) receptor partial agonist to be approved for the treatment of this syndrome. Tegaserod is active against multiple irritable bowel syndrome (IBS) symptoms; it stimulates gut motility and reduces visceral sensitivity and pain. The drug does not cure IBS and was not designed to treat the diarrhoea-predominant version. Its efficacy in men has not been established. Three large well designed clinical trials of tegaserod 6 mg twice daily for 12 weeks in patients (mainly women) with IBS-C have demonstrated superiority versus placebo in global relief from symptoms. Global relief response rates were 38.4-46.8% with tegaserod 6 mg twice daily and 28.3-38.8% with placebo (p < 0.05-0.0001 vs placebo). The relative increases in response rates with tegaserod 6 mg twice daily over the already high responses in the placebo groups ranged from 12-65% after 4-12 weeks of treatment. A response was seen within the first week. The proportion of patients with satisfactory relief from symptoms fell over the 4-week period following withdrawal of tegaserod and placebo, but did not reach baseline levels during this time. Diarrhoea has been associated with tegaserod in clinical trials (an incidence of about 10% versus 5% with placebo, usually occurring in the first week of treatment), but the drug is otherwise well tolerated. There were no apparent changes in the tolerability profile with extended tegaserod treatment (</=12 months). In conclusion, oral tegaserod 6 mg twice daily for 12 weeks is effective and well tolerated in the treatment of IBS-C in women. Data on long term and comparative efficacy, cost-effectiveness and quality-of-life effects would be beneficial; however, in light of the fact that very few alternatives for the treatment of IBS-C have proven efficacy, tegaserod appears to be a promising option in women not responding to increased dietary fibre or osmotic laxative therapy.

Gastric function measurements in drug development

The function of the stomach includes initiation of digestion by exocrine secretions such as acid and pepsin, which are under the control of the endocrine secretion of hormones that also coordinate intestinal motility. The stomach also stores and mechanically disrupts ingested food. Various techniques have been developed to assess gastric physiology, the most important of which is assessment of acid secretion, as well as gastric motility and gastric emptying. The influence of drugs on gastric function and the effect of gastric secretion and mechanical actions on the bioavailability of novel compounds are of critical importance in drug development and hence to clinical pharmacologists. The control of acid secretion is essential in the treatment of peptic ulcer disease as well as gastrooesophageal reflux disease (GORD); pH-metry can be used to determine the necessary dose of an acid suppressant to heal mucosal damage. Disturbed gastric myoelectric activity leading to gastroparesis can cause delayed gastric emptying, often found in patients with diabetes mellitus. Electrogastrography (EGG) may be used to evaluate the influence of prokinetics and other drugs on this condition and aid in determining effective therapy.

Clinical pharmacokinetics of tegaserod, a serotonin 5-HT(4) receptor partial agonist with promotile activity

Tegaserod, a selective serotonin (5-hydroxytryptamine; 5-HT) 5-HT(4) receptor partial agonist, is indicated in patients with irritable bowel syndrome (IBS) who identify abdominal pain or discomfort and constipation as their predominant symptoms. Tegaserod at dosages of 1 to 12 mg/day exerts pharmacodynamic actions in the upper and the lower gastrointestinal tract, accelerating small bowel and colonic transit in patients with IBS. Tegaserod is rapidly absorbed following oral administration; peak plasma concentrations (C(max)) are reached after approximately 1 hour. Absolute bioavailability is about 10% under fasted conditions. Food reduces the bioavailability of tegaserod by 40 to 65% and the C(max) by 20 to 40%. Systemic exposure to tegaserod is not significantly altered at neutral gastric pH compared with the fasted state (pH 2). Tegaserod is approximately 98% bound to plasma proteins, primarily to alpha(1)-acid glycoprotein, and has a volume of distribution at steady-state of 368 +/- 223L. Tegaserod is metabolised mainly via two pathways. The first is a presystemic acid-catalysed hydrolysis in the stomach followed by oxidation and conjugation which produces the main metabolite of tegaserod, 5-methoxyindole-3-carboxylic acid glucuronide (M 29.0). This metabolite has negligible affinity for 5-HT(4) receptors and is devoid of promotile activity. The second is direct glucuronidation which leads to generation of three isomeric N-glucuronides. The plasma clearance of tegaserod is 77 +/- 15 L/h, with an estimated terminal half-life of 11 +/- 5 hours following intravenous administration. Approximately two-thirds of the orally administered dose of tegaserod is excreted unchanged in faeces, with the remainder excreted in urine, primarily as M 29.0. The pharmacokinetics of tegaserod are dose-proportional over the range 2 to 12mg given twice daily for 5 days, with no relevant accumulation. The pharmacokinetics of tegaserod in patients with IBS are comparable to those in healthy individuals, and similar between men and women. No dosage adjustment is required in elderly patients or those with mild to moderate hepatic or renal impairment. Tegaserod should not be used in patients with severe hepatic or renal impairment. No clinically relevant drug-drug interactions with tegaserod have been identified. In vivo drug-drug interaction studies with theophylline [a cytochrome P450 (CYP) 1A2 prototype substrate], dextromethorphan (a CYP2D6 prototype substrate), digoxin, warfarin and oral contraceptives have indicated no clinically relevant interactions and no requirement for dosage adjustment.

Tegaserod pharmacokinetics are similar in patients with severe renal insufficiency and in healthy subjects

Tegaserod (HTF 919), a selective 5-HT4 receptor partial agonist with promotile activity throughout the gastrointestinal tract, is in development for the treatment of irritable bowel syndrome. In an open-label, parallel-group study, the pharmacokinetics of a single 12-mg oral dose of tegaserod in patients with severe renal insufficiency requiring hemodialysis were compared with data obtained from healthy subjects matched for age, weight, height, and gender (n = 10, both). The pharmacokinetics of tegaserod were similar in both groups (AUC(0h-tz), ng.h/ml: 14.6 +/- 8.5 vs. 14.3 +/- 7.1; Cmax, ng/ml: 4.6 +/- 2.3 vs. 5.1 +/- 2.2; tmax, h: 1.0, for both). Tegaserod had similar tolerability in renally impaired patients and healthy volunteers, with adverse events largely related to the gastrointestinal pharmacological actions of the drug. Therefore, no dose adjustment of tegaserod is necessary for patients with renal insufficiency.

Tegaserod, a 5-hydroxytryptamine type 4 receptor partial agonist, is devoid of electrocardiographic effects

OBJECTIVES

Certain GI prokinetic agents have been shown to affect cardiac repolarization, which may be associated with life-threatening arrhythmias. The selective 5-hydroxytryptamine type 4 receptor partial agonist tegaserod is a novel promotile agent developed for the treatment of functional motility disorders such as irritable bowel syndrome (IBS). The aim of the study was to investigate the cardiac safety profile of tegaserod through analysis of electrocardiographic data from clinical studies conducted in patients with IBS and a study conducted in healthy male subjects.

METHODS

In three randomized, double blind, placebo-controlled, parallel group clinical studies, 2516 IBS patients with symptoms of abdominal pain and constipation received tegaserod 2 or 6 mg b.i.d. (n = 1679) or placebo (n = 837) for 12 wk. In an additional study, 36 healthy male subjects received iv. single doses of tegaserod (0.8 mg to 20 mg) or placebo. Standard 12-lead electrocardiograms were recorded at baseline and during treatment. Baseline values were compared with data collected during the treatment period.

RESULTS

The proportion of patients with prolongation of the QTc interval was the same for placebo and tegaserod, as was the frequency of overall electrocardiographic abnormalities. No ventricular or supraventricular tachycardia was observed. Comparable electrocardiographic results were obtained during placebo and tegaserod treatment. In healthy volunteers, tegaserod at i.v. doses resulting in plasma concentrations up to 100 times those measured after therapeutic doses (6 mg b.i.d.) did not influence electrocardiographic parameters.

CONCLUSIONS

Tegaserod is devoid of electrocardiographic effects and is not expected to adversely influence cardiac function. These data confirm preclinical findings.

Tegaserod: a new 5-HT(4) agonist in the treatment of irritable bowel syndrome

Tegaserod is a selective partial agonist acting on serotonergic type 4 receptors (5-HT(4)). Pharmacodynamic studies indicate that tegaserod is able to stimulate gut propulsion and secretion with a net prokinetic effect. In contrast to other 5-HT(4) agonists endowed with a complex pharmacological profile, tegaserod has a reliable prokinetic activity in the colon. Clinical trials show that tegaserod is effective and safe in the treatment of patients with irritable bowel syndrome. In particular, tegaserod relieves symptoms of abdominal pain, discomfort, abdominal bloating and constipation.

Clinical perspectives, mechanisms, diagnosis and management of irritable bowel syndrome

This consensus document reviews the current status of the epidemiology, social impact, patient quality of life, pathophysiology, diagnosis and treatment of irritable bowel syndrome. Current evidence suggests that two major mechanisms may interact in irritable bowel syndrome: altered gastrointestinal motility and increased sensitivity of the intestine. However, other factors, such as psychosocial factors, intake of food and prior infection, may contribute to its development. Management of patients is based on a positive diagnosis of the symptom complex, careful history and physical examination to exclude 'red flags' as risk factors for organic disease, and, if indicated, investigations to exclude other disorders. Therapeutic choices include dietary fibre for constipation, opioid agents for diarrhoea and low-dose antidepressants or infrequent use of antispasmodics for pain, although the evidence basis for efficacy is limited or in some cases absent. Psychotherapy and hypnotherapy are the subject of ongoing study. Treatment should be tailored to patient needs and fears. Novel therapies are emerging, and drugs acting on serotonin receptors have proven efficacy and a scientific rationale and, if approved, should be useful in the overall management of patients with irritable bowel syndrome. Patient and physician education, early identification of psychosocial issues and better therapies are important strategies to reduce the suffering and societal cost of irritable bowel syndrome.

Irritable bowel syndrome: basis of clinical management strategies

Patients with irritable bowel syndrome (IBS) are often described as challenging. The diagnosis of IBS can safely be made using the Rome II criteria in conjunction with a thorough physical examination and a limited number of diagnostic studies. Although the diagnosis is generally made with a high degree of accuracy, the pathophysiology of IBS remains elusive, and treatment can be frustrating for both patient and physician alike. Important areas of research focus on the psychology of IBS, visceral hypersensitivity, motility abnormalities (e.g., heightened gastrocolonic response), and the "brain-gut axis." A multidisciplinary effort is often required to ameliorate symptoms and improve the patients' quality of life. This review article will discuss the myriad of treatments available for patients with IBS, and provide both a clinical and practical discussion of their use, providing evidence where available and clinical experience where it is not.

Safety and tolerability of tegaserod in patients with irritable bowel syndrome and diarrhea symptoms

OBJECTIVES

Tegaserod is a selective serotonin (5-HT4) receptor partial agonist effective in providing relief from abdominal pain, bloating, and constipation in patients with irritable bowel syndrome. Tegaserod therapy may be associated with early transient diarrhea, which is related to its mechanism of action. This study was performed in patients with irritable bowel syndrome and symptoms of diarrhea to further assess the safety of tegaserod.

METHODS

After a 2-wk baseline, patients were randomized (2:2:1) in a double-blind manner to receive 4 mg of tegaserod a day (n = 35), 12 mg of tegaserod a day (n = 34), or placebos (n = 17) for 8 wk. Patients had to fulfill > or =2 Rome diarrhea criteria > or =25% of the time. Adverse events were recorded.

RESULTS

Diarrhea, abdominal pain, headache, flatulence, and fatigue were the most frequently reported adverse events. The frequency rates of diarrhea were 49%, 18%, and 35% for the 4 mg/day, 12 mg/day, and placebo groups, respectively; when the tegaserod data were pooled, the frequency of diarrhea was similar to that of the placebo group (33% and 35%, respectively). No complications of diarrhea (e.g., dehydration and electrolyte abnormalities) were reported. Five patients (6%), all from the tegaserod groups, discontinued study participation because of diarrhea and/or abdominal pain. No serious adverse events were reported.

CONCLUSIONS

In this study, tegaserod at doses of 4 and 12 mg/day was safe and not associated with complications of diarrhea or serious adverse events.

Tegaserod: a new 5-HT4 agonist

Tegaserod is a medication that has been shown to be of benefit in women with irritable bowel syndrome (IBS) associated with abdominal pain, bloating, and constipation. Tegaserod is a selective serotonin receptor subtype 4 partial agonist designed to interact with the network of cells and nerves throughout the gastrointestinal tract that use serotonin. Tegaserod has been shown to modulate both gastrointestinal motility and visceral sensitivity. Specifically, it increases the peristaltic reflex and decreases visceral sensitivity. Clinical studies have shown that tegaserod improves symptoms of abdominal pain, bloating, and constipation in women with IBS. This article discusses the role of serotonin in gastrointestinal tract physiology, the structure and pharmacokinetic profile of tegaserod, and clinical applications of this new drug.

Impact of irritable bowel syndrome on personal relationships and working practices

OBJECTIVE

To determine the impact of irritable bowel syndrome on personal relationships and working practices.

PATIENTS AND METHODS

A 60-item questionnaire about personal relationships, working practices and treatment was sent to 3090 subscribers of the IBS Bulletin, a quarterly educational publication. A total of 1855 completed questionnaires were returned. Analysis was restricted to 1597 questionnaires (86.1%), returned by respondents in whom the diagnosis of irritable bowel syndrome had been made by a general practitioner or hospital specialist.

RESULTS

Of these respondents, 57% were aged 55 or over and the male to female ratio was 1:3.4. On average, respondents had suffered from irritable bowel syndrome for 16.6 years, with 57% reporting their symptoms daily, 25% weekly and 14% monthly. Of the married or cohabiting respondents, 19% stated that their partner experienced difficulties in having a personal relationship with them and 45% stated that irritable bowel syndrome interfered with their sex life. Irritable bowel syndrome had caused 12% of respondents to give up work altogether, while 47% of employed respondents reported having lost time off work, although only 35% of these respondents gave irritable bowel syndrome as the reason. In contrast employers, when informed of the diagnosis of irritable bowel syndrome, accepted these symptoms as a valid reason for absence in 61% of instances. Over half of those employed (53%) suffered embarrassment using toilets at work and 32% stated that irritable bowel syndrome had stopped them from applying for promotion or a new job. At the time of completing the questionnaire, 80% of respondents were actually taking some form of treatment. Smooth-muscle relaxants and fibre supplements remained the commonest treatments prescribed.

CONCLUSION

Irritable bowel syndrome impacts significantly on personal relationships and working practices. Items that stimulate responsiveness in the areas of personal relationships and working practices should be included in the construction of disease-specific questionnaires used to assess the impact of new treatments for irritable bowel syndrome on health-related quality of life.

The effects of tegaserod (HTF 919) on the pharmacokinetics and pharmacodynamics of digoxin in healthy subjects

Tegaserod (HTF 919) is a highly specific 5-HT4 receptor partial agonist that exhibits promotile activity throughout the gastrointestinal tract and is under development for the treatment of functional gastrointestinal motility disorders. The present study was designed to assess the effect of multiple doses of tegaserod on the single-dose pharmacokinetics and pharmacodynamics of digoxin, a commonly prescribed agent for congestive heart failure. The study was an open-label, randomized, two-period crossover design of 12 healthy subjects. One treatment included digoxin treatment alone; the other treatment included a combined digoxin and tegaserod treatment. On day 1 of the digoxin treatment period, subjects received a single 1 mg oral dose of digoxin. In the combined tegaserod/digoxin treatment period, subjects received a single oral dose of 1 mg digoxin after 3 days of tegaserod (6 mg bid). After coadministration of tegaserod, systemic exposure to digoxin was decreased; mean AUC decreased by 11.9% (p < 0.05) relative to digoxin alone. Cmax was decreased by about 15% (p < 0.05). The 0.5-hour difference in the median tmax between the two treatments was not statistically significant. Because the steady-state trough concentration of digoxin (C(SS,min)) correlates with pharmacological effects, C(SS,min) for digoxin alone and in combination with tegaserod was simulated based on both parametric compartmental modeling and nonparametric superpositioning approaches. The predicted arithmetic mean C(SS,min) for combination therapy is 86% to 89% of that following digoxin alone. Likewise, the predicted arithmetic mean steady-state peak concentration (C(SS,min)) and AUC at steady state during a dosing interval (AUC(SS,tau)) have a similar decrease. This extent of decrease in systemic exposure of digoxin at steady state is unlikely to be clinically relevant. Administration of tegaserod (6 mg bid) was well tolerated, both alone and in combination with a single dose of digoxin. There were no pharmacodynamic changes in ventricular rate and QT interval following coadministration of tegaserod with digoxin. The 1.5-hour and 2-hour postdose plasma concentrations of tegaserod on days 3 and 4 confirmed adequate exposure. In conclusion, dose adjustment for digoxin is unlikely to be needed when tegaserod is coadministered.

Effects of the enterokinetic prucalopride (R093877) on colonic motility in fasted dogs

The novel enterokinetic drug prucalopride was tested at various intravenous and oral doses in fasted dogs to assess: (i) the effects on colonic contractile motility patterns; and (ii) the mediation of these effects by 5-hydroxytryptamine (5-HT4) receptors. Colonic motility patterns were assessed in conscious dogs with four chronically implanted strain-gauge force transducers that were sutured on the serosal side of the colon. Prucalopride altered colonic contractile motility patterns in a dose-dependent fashion by stimulating high-amplitude clustered contractions in the proximal colon and by inhibiting contractile activity in the distal colon. Prucalopride was equipotent after oral and intravenous administration, as reflected by the values for the effective dose that induced 50% of maximum effect (95% confidence limits): 0.04 mg kg(-1) p.o. (0.01-0.1 mg kg(-1)) and 0.01 mg kg(-1) i.v. (0.006-0.04 mg kg(-1)). Prucalopride also caused a dose-dependent decrease in the time to the first giant migrating contraction (GMC); at higher doses of prucalopride, the first GMC generally occurred within the first half-hour after treatment. Subcutaneous pretreatment with the 5-HT4 receptor antagonist GR125487 (40 microg kg(-1) bodyweight) completely prevented the effects of orally administered prucalopride (0.31 mg kg(-1) bodyweight). Prucalopride, given orally or intravenously, alters colonic motility in the fasted conscious dog in a dose-dependent fashion. It induces GMCs and causes proximal colon stimulation and distal colon inhibition of contractile motility patterns by stimulating 5-HT4 receptors.

Irritable bowel syndrome: new agents targeting serotonin receptor subtypes

Although the past few years have seen an exponential growth of compounds of potential interest for the treatment of functional gastrointestinal (GI) tract disorders, the gap that still exists between basic and clinical research is easily noticed if one considers the relative paucity of drugs that have received marketing authorisation for the treatment of irritable bowel syndrome (IBS). Traditional efficacy outcomes in drug development for IBS include the ability of the compound to affect GI tract motility (i.e. to exert a prokinetic or an antispasmodic effect), which is thought to be of importance if a motor disorder is the underlying pathophysiological mechanism. More recently, altered visceral sensitivity to a distending stimulus has been suggested to be a key pathophysiological feature, at least in some patients, and has become a target for therapeutic interventions. However, there is now growing consensus that the primary outcome measure in the treatment of functional disorders are those that reflect overall control of the patient's symptoms (pain, diarrhoea, constipation) in everyday situations such as the clinical global improvement scales. Although, in general, guidelines on the design of treatment trials for functional GI tract disorders advise against subcategorisation of patients according to the main symptom (because of symptom instability), subcategorisation indeed makes sense especially in IBS (constipation- or diarrhoea-predominant). Compounds with a specific indication for each subpopulation of patients are now emerging. The rationale for investigations on serotonin (5-hydroxytryptamine; 5-HT) receptor ligands in IBS rests mainly on the fact that serotonin, which may be released by enterochromaffin-like cells in the GI tract as well as from other sources, has a number of well documented motor effects on the GI tract and can produce hyperalgesia in several experimental models. Serotonin receptors belonging to the 5-HT3 and 5-HT4 subtype are the most extensively studied in gastroenterology, although hitherto 'orphan' receptor subtypes, such as the 5-HT7 and the 5-HT(1B/D) receptors, are now emerging. Among 5-HT3 receptor antagonists, alosetron was recently approved for the treatment of diarrhoea-predominant IBS and is an example of a compound that, at least theoretically, may act at multiple levels: by inhibiting visceral sensitivity, by increasing compliance, and by inhibiting excitatory 5-HT3 receptors located on both ascending and descending neuronal pathways involved in peristalsis. For this reason, 5-HT3 receptor antagonists may slow transit, hence the specific indication of alosetron in diarrhoea-predominant IBS. However, alosetron has been recently withdrawn by the manufacturer because of safety concerns. Hypomotility remains an attractive therapeutic target in IBS and the new generation of prokinetics includes several partial agonists at the 5-HT4 receptor, such as tegaserod (HTF-919) and prucalopride (R0-93877). In addition, preliminary evidence suggests that 5-HT4 receptors may also be involved in the modulation of visceral sensitivity. Second-generation 5-HT4 receptor agonists seem to be devoid of the QT-prolonging effects observed in some clinical circumstances with cisapride and may be more active at the colonic level. Piboserod (SB-207266A) is a 5-HT4 receptor antagonist under development for the treatment of diarrhoea-predominant IBS. Finally, interest in 5-HT7 and 5-HT(1B/D) receptor subtypes stems from the observation that the former receptors mediate smooth muscle relaxation (at least in the human colon), whereas sumatriptan (a 5-HT(1B/D) receptor agonist) can affect GI tract motility and visceral sensitivity.

Review article: tegaserod

Tegaserod (Zelmac), an aminoguanidine indole derivative of serotonin, is a selective partial agonist highly selective for 5-HT(4) receptor with an affinity constant in the nanomolar range. Tegaserod does not cause adverse pharmacodynamic effects, is absorbed rapidly after oral administration and distributes widely into tissues. Pharmacokinetics of oral tegaserod are linear in the 2--12 mg dose range. After oral administration tegaserod is metabolized mainly pre-systemically; when absorbed, intact tegaserod is excreted as N-glucuronides mainly via the bile. No clinically relevant drug--drug interactions were identified. Tegaserod has proven safe in toxicity studies. In pharmacodynamic studies, tegaserod stimulated the peristaltic reflex in vitro, increased canine intestinal and colonic motility and transit, reduced visceral afferent firing or sensation in response to distension in animals, and accelerated gastric, small bowel and colonic transit in healthy patients, and small bowel transit in patients with constipation-predominant irritable bowel syndrome. Three large phase III randomized, double-blinded, and placebo-controlled trials were performed predominantly in females (approximately 85%) with constipation-predominant irritable bowel syndrome. Overall, phase III results support efficacy as assessed by the subject's global assessment of relief with significant improvement in secondary endpoints such as abdominal pain, bowel frequency and consistency. Tegaserod was well-tolerated; the most frequent adverse event was transient diarrhoea.

An improved in vitro bioassay for the study of 5-HT(4) receptors in the human isolated large intestinal circular muscle

Recently, it was demonstrated that 5-HT induces relaxation of human colon circular muscle through activation of 5-HT(4) receptors and 5-HT(7) receptors. The aim of the current study was to develop a new in vitro bioassay of human colon that would facilitate the pharmacological analysis of 5-HT responses mediated solely by 5-HT(4) receptors. Contracting circular muscle strips with KCl (80 mM) yielded a stable contractile tension and, in contrast to muscarinic cholinoceptor agonists and histamine, a profound reduction of spontaneous contractility. This allowed the establishment of reproducible, fully-defined, agonist concentration-response curves by cumulative dosing. Under these conditions, 5-HT induced a concentration-dependent relaxation (pEC(50) 7.31, Hill slope 0.91). Neither methysergide (10 microM) nor granisetron (1 microM) affected the 5-HT-induced relaxation, suggesting that 5-HT(1), 5-HT(2), 5-HT(3), 5-ht(5), 5-HT(6) or 5-HT(7) receptors are not involved. The lack of effect of tetrodotoxin (0.3 microM) indicated a direct effect of 5-HT on the smooth muscle. The selective 5-HT(4) receptor antagonists GR 113808, GR 125487 and RS 39604 competitively antagonized the 5-HT-induced relaxation (pK(B) 9.43, 10.12 and 8.53, respectively). SB 204070 (1 nM) produced a rightward shift (pA(2) 10.34) and depression of the 5-HT curve. These affinity estimates are similar to those previously reported for 5-HT(4) receptors. The selective 5-HT(4) receptor agonists, prucalopride and R076186, induced relaxations (pEC(50) 7.50 and 7.57, respectively), that were blocked by GR 113808 (3 nM), yielding pA(2) estimates of 9.31 and 9.21, respectively. To summarise, in KCl (80 mM)-contracted muscle strips, 5-HT induces relaxation through activation of a homogeneous smooth muscle 5-HT(4) receptor population. This new bioassay allows the focused, pharmacological characterization of human colonic 5-HT(4) receptors in vitro.

Tegaserod accelerates orocecal transit in patients with constipation-predominant irritable bowel syndrome

BACKGROUND & AIMS

This study evaluated the effects of a partial 5-hydroxytryptamine (5-HT)(4) agonist, tegaserod, on gastric small bowel and colonic transit in constipation-predominant irritable bowel syndrome (IBS).

METHODS

After a 1 week run-in period, 24 patients with constipation-predominant IBS were randomized to 1 week of tegaserod, 2 mg twice daily, or placebo treatment. Scintigraphic gastric emptying, small bowel transit, and colonic transit were determined before administration of study drug and after 1 week on the medication. Colonic transit was also measured using radiopaque markers and a single radiograph on day 5.

RESULTS

Gastric emptying was unaltered by tegaserod. Proximal colonic filling at 6 hours, a measure of orocecal transit, was accelerated by tegaserod (70.4% +/- 1.3% [mean +/- SEM] vs. placebo, 46.4 +/- 1.9; P = 0.015). Proximal colonic emptying half-time and geometric center at 48 hours were also accelerated by tegaserod compared with baseline, but not compared with placebo. Mean colonic transit time was similar in both groups at baseline and after drug administration (tegaserod, 59.5 +/- 2.1 hours; placebo, 62.1 +/- 2.1 hours).

CONCLUSIONS

Tegaserod accelerates orocecal transit, tends to accelerate colonic transit, and deserves further study in patients with constipation-predominant IBS.

Tegaserod

Tegaserod is a serotonin (5-hydroxytryptamine; 5-HT) receptor partial agonist which has been investigated for the treatment of irritable bowel syndrome (IBS). Specifically, it binds with high affinity to human 5-HT4 receptors, thereby stimulating the release of neurotransmitters and the peristaltic reflex in vitro. Small bowel transit (increased colonic filling over 6 hours) was accelerated in patients with constipation-predominant irritable bowel syndrome (IBS) receiving oral tegaserod 2mg twice daily for 1 week compared with those receiving placebo. In addition, there was a mean 20% increase of proximal colonic emptying in these patients. Oral tegaserod 2 (p < 0.05) or 6mg twice daily improved symptoms of abdominal discomfort, bloating and constipation (assessed using a Subjects' Global Assessment Scale) compared with placebo in patients with constipation-predominant IBS in a double-blind, dose-ranging study. The most frequent adverse events in patients with constipation-predominant IBS receiving oral tegaserod were transient diarrhoea and flatulence. No clinically relevant changes in blood pressure, pulse rate, QRS or QTc interval were reported with tegaserod doses of 25 to 100mg.

Effect of meal timing not critical for the pharmacokinetics of tegaserod (HTF 919)

This study assessed the pharmacokinetic profiles of administering tegaserod (HTF 919) at different time intervals with respect to a meal. It was a randomized, open-label, two-phase, five-period crossover study. In the first phase, 18 healthy subjects received a single 12 mg oral dose of tegaserod administered either 30 or 15 minutes prior to the start of the 600-calorie, fat-rich breakfast. In the second phase, subjects received a single 12 mg oral dose of tegaserod 1 minute before, 2.5 hours after the start of meal, or with a continued 4-hour postdose fast. Safety assessment and plasma samples for the determination of drug concentration were obtained for 24 hours postdose. Noncompartmental analysis results indicated that the AUC of tegaserod was reduced by almost half under fed conditions compared to the fasted condition. Exploratory analyses were implemented to further investigate the absorption characteristics of tegaserod under different fed conditions. A numerical deconvolution approach was used to obtain the tegaserod oral absorption versus time profiles under both fasted and fed conditions. The tegaserod oral absorption versus time profiles were then fitted by NONMEM to a model containing two absorption phases. Based on the absorption analyses, we found that the reduction in the bioavailability of tegaserod under fed conditions was primarily due to a decrease in the extent of absorption and less so to a decrease in the absorption rate(s). Therefore, although the timing of administration of food does not appear to significantly alter the pharmacokinetics of tegaserod, the administration of food reduces the AUC by approximately 50%.

Integrated modelling of the clinical pharmacokinetics of SDZ HTF 919, a novel selective 5-HT4 receptor agonist, following oral and intravenous administration

AIMS

The purpose of the present study was to assess the pharmacokinetics of the novel selective 5-HT4 receptor agonist SDZ HTF 919 (HTF) including food effect, absolute bioavailability, interoccasion and intersubject variabilities.

METHODS

In the randomized, open-label, three treatment, four period crossover study, HTF was administered to 12 young healthy male subjects as a 12 mg tablet (twice under fasted and once under fed conditions) and a 3 mg intravenous (i.v.) infusion over 40 min (fasted). Pharmacokinetic parameters were obtained by noncompartmental methods. A more comprehensive pharmacokinetic characterization was achieved by integrated modelling of oral (p.o.) and i.v. data. To describe the absorption phase a Weibull function and a classical first order input function were compared.

RESULTS

Noncompartmental pharmacokinetic analysis revealed a rapid absorption (tmax 1.3 h, fasted), an absolute bioavailability of 11+/-3%, a biphasic disposition phase with a terminal half-life of 11+/-5 h, a clearance of 77+/-15 l h-1, and a volume of distribution at steady state of 368+/-223 l. The coefficients of interoccasion and interindividual variability in Cmax and AUC ranged between 17 and 28%. Food intake caused a delay (tmax 2.0 h) and decrease in absorption with consequently lower systemic exposure ( approximately 5% absolute bioavailability). Integrated p.o./i.v. pharmacokinetic modelling with a Weibull input function allowed accurate description of individual profiles. Modelling of the data from the p.o. dosing improved the description of the terminal phase by inclusion of the i. v. data and additionally provided quantitative characterization of the absorption phase.

CONCLUSIONS

The pharmacokinetics of HTF could be well described by an integrated modelling approach for both p.o. and i.v. data. The derived model will provide guidance in the design of future studies.

Mediators and regulation of peristalsis

Peristalsis is the main postprandial propulsive activity of the gut. It is mediated by neurons of the enteric nervous system, which form an integrated circuit composed of sensory neurons, modulatory interneurons, and motor neurons to the circular and longitudinal muscle layers. Work outlined in this review has identified, by anatomic, physiologic, and pharmacologic techniques, the myenteric neurons and neurotransmitters involved in the regulation of this reflex. Of particular note are studies identifying the role of 5-hydroxytryptamine4 (5-HT4) receptors in the initiation of the peristaltic reflex and the development of selective 5-HT4 agonists as potential therapeutic agents.

Idiopathic constipation: too few stools and too little knowledge

The precise abnormalities of colonic motility patterns in idiopathic constipation, and the alterations at the cellular, neural, myogenic and biochemical levels that underlie these patterns, are not yet understood. One promising approach in the treatment of constipation seems to be to design drugs that can stimulate GMCs to produce mass movements and consequently defaecation. This could possibly be achieved with the selective 5-HT4 receptor agonists prucalopride and SDZ HTF-919, which are currently in advanced clinical trials. Other mechanisms that provide a means to induce GMCs, such as NK1 receptor agonism, deserve further exploration.

SB-207266: 5-HT4 receptor antagonism in human isolated gut and prevention of 5-HT-evoked sensitization of peristalsis and increased defaecation in animal models

SB-207266 is a new 5-HT4 receptor antagonist which in a pilot study reduced the symptoms of irritable bowel syndrome. To help validate this and further studies, we examined the ability of SB-207266 to antagonize at the human 5-HT4 receptor (human isolated intestine) and to affect the mechanisms of peristalsis (guinea-pig isolated ileum) and defaecation (conscious, fed mice). In the human intestine, the potency of 5-HT4 receptor antagonism (pKB 9.98) was similar to that previously demonstrated using a guinea-pig model of the receptor, validating the use of SB-207266 in clinical trials. In each of the animal models, SB-207266 did not affect normal patterns of intestinal motility measured in the absence of exogenous 5-HT. However, SB-207266 10-1000 pM concentration-dependently antagonized the ability of 5-HT (0.1 microM) to sensitize the peristaltic reflex and lower the distension threshold at which peristalsis was evoked. In mice, oral or subcutaneous (s.c.) doses of SB-207266 dose-dependently prevented the ability of the 5-HT precursor, 5-hydroxytryptophan (5-HTP, 10 mg kg-1 s.c.) to increase both the rate of defaecation of formed faecal pellets and their fluid content. SB-207266 was maximally active at 10 micrograms kg-1 s.c. and 1000 micrograms kg-1 p.o. SB-207266 may therefore represent a new class of therapeutic agent, capable of preventing the actions of an important sensitizer of gut function.

5-Hydroxytryptamine4 receptor agonists initiate the peristaltic reflex in human, rat, and guinea pig intestine

BACKGROUND & AIMS

The peristaltic reflex induced by mucosal stimuli is mediated by intrinsic sensory calcitonin gene-related peptide (CGRP) neurons activated by 5-hydroxytryptamine (5-HT) released from enterochromaffin cells. The involvement of 5-HT4 receptors was examined with selective 5-HT4 agonists.

METHODS

Compartmented intestinal segments were used to measure neurotransmitter release and the mechanical components of the reflex.

RESULTS

In human jejunal and rat and guinea pig colonic segments, addition of the 5-HT4 agonist HTF 919 elicited release of CGRP only into the compartment where the 5-HT4 agonist was added; vasoactive intestinal peptide (VIP) was released only into the compartment where descending relaxation was measured, and substance P (SP) was released only into the compartment where ascending contraction was measured. The CGRP antagonist hCGRP8-37 inhibited both mechanical responses by 75%-80%. Release of CGRP, VIP, and SP as well as ascending and descending responses were inhibited by selective 5-HT4 but not by selective 5-HT3 antagonists. Similar results were obtained with a different 5-HT4 agonist, R093877. However, HTF 919 was 10-30 times more potent (median effective concentration, approximately 10 nmol/L for peptide release and 5 nmol/L for mechanical responses) than R093877.

CONCLUSIONS

Selective 5-HT4 agonists applied to the mucosa in nanomolar concentrations trigger the peristaltic reflex in human, rat, and guinea pig intestine.

Clinical pharmacodynamics of SDZ HTF 919, a new 5-HT4 receptor agonist, in a model of slow colonic transit

OBJECTIVES

To explore the pharmacodynamic effects of the new promotile agent SDZ HTF 919, a selective partial 5-HT4 receptor agonist, in healthy subjects.

METHODS

A pharmacodynamic model was applied to prolong colonic transit by dietary means. Subsequently, the effects of twice-daily multiple doses of SDZ HTF 919 (1, 5, 25, and 100 mg) were investigated in a randomized, double-blind, placebo-controlled parallel-group study with 12 subjects per dose level. The sequential design with three study periods of 7 days each included intake of a self-selected diet, a liquid formula diet with soluble fiber supplementation, and a fiber-supplemented diet together with either SDZ HTF 919 or placebo administration. Stool characteristics (frequency and consistency) and total colonic transit times (with use of radiopaque markers) were recorded in each study period.

RESULTS

SDZ HTF 919 was well tolerated at all dose levels. The frequency of loose stool and headache increased with higher doses. After a fiber-supplemented diet intake, the median stool frequency decreased from 8 1/2-9 to 5-7 defecations per study period. SDZ HTF 919 in doses of 25 and 100 mg twice a day increased the stool frequency (p < 0.05). Stool consistency was softened by all but the lowest SDZ HTF 919 dose. A fiber-supplemented diet prolonged total colonic transit time in all groups by 45 hours on average. Twice-a-day administration of SDZ HTF 919 for 6 days in addition to a fiber-supplemented diet significantly shortened the total colonic transit time only at the 5 mg dose. The lack of effect at lower and higher SDZ HTF 919 doses suggests a biphasic dose-response relationship for total colonic transit time.

CONCLUSIONS

The suitability of total colonic transit time measurements in healthy subjects as a surrogate marker should be confirmed by patient studies.