Racecadotril versus placebo in the treatment of acute diarrhoea in adults

Enkephalinase inhibitors, potential therapeutics for the future treatment of diarrhea predominant functional gastrointestinal disorders

The endogenous opioid system (EOS) is considered being a crucial element involved in the pathophysiology of irritable bowel syndrome (IBS) as it regulates gastrointestinal (GI) homeostasis through modulation of motility and water and ion secretion/absorption. Along with opioid receptors (ORs), the following components of EOS can be distinguished: 1. endogenous opioid peptides (EOPs), namely enkephalins, endorphins, endomorphins and dynorphins, and 2. peptidases, which regulate the metabolism (synthesis and degradation) of EOPs. Enkephalins, which are δ-opioid receptors agonists, induce significant effects in the GI tract as they act as potent pro-absorptive neurotransmitters. The action of enkephalins and other EOPs is limited, since EOPs are easily and rapidly inactivated by a natural metalloendopeptidase (enkephalinase/neprilysin) and aminopeptidase N. Studies show that the activity of EOPs can be enhanced by inhibition of these enzymes. In this review, we discuss the antidiarrheal and antinociceptive potential of enkephalinase inhibitors. Furthermore, our review is to answer the question whether enkephalinase inhibitors may be helpful in the future treatment of diarrhea predominant functional GI disorders.

Stand-by antibiotics encourage unwarranted use of antibiotics for travelers' diarrhea: A prospective study

BACKGROUND

As antibiotics predispose travelers to acquiring multidrug-resistant intestinal bacteria, they should no longer be considered a mainstay for treating travelers' diarrhea. It has been claimed that stand-by antibiotics are justified as a means to avoid visits to local healthcare providers which often lead to polypharmacy.

METHOD

We revisited the traveler data of 316 prospectively recruited volunteers with travelers' diarrhea by retrieving from questionnaires and health diaries information on antibiotic use, stand-by antibiotic carriage, and visits with local healthcare. Multivariable analysis was applied to identify factors associated with antibiotic use.

RESULTS

Among our 316 volunteers with travelers' diarrhea, however, carrying stand-by antibiotics seemed not to reduce the rate of healthcare-seeking; on the contrary, antibiotic use was more frequent among stand-by antibiotic carriers (34%) than non-carriers (11%). Antibiotics were equally taken for severe and incapacitating travelers' diarrhea, but compared to non-carriers, stand-by antibiotic carriers resorted to medication also for mild/moderate (38% vs. 4%) and non-incapacitating disease (29% vs. 5%). Antibiotic use was associated with stand-by antibiotic carriage (OR 7.2; 95%CI 2.8-18.8), vomiting (OR 3.5; 95%CI 1.3-9.5), incapacitating diarrhea (OR 3.6; 95%CI 1.3-9.8), age (OR 1.03; 95%CI 1.00-1.05), and healthcare visit for diarrhea (OR 465.3; 95%CI 22.5-9633.6).

CONCLUSIONS

Carriage of stand-by antibiotics encouraged less cautious use of antibiotics. Recommendations involving prescription of antibiotics for all travelers require urgent revision.

Racecadotril in the treatment of acute diarrhea in children: a systematic, comprehensive review and meta-analysis of randomized controlled trials

BACKGROUND

Racecadotril is a guideline-recommended option for the treatment of acute diarrhea in children but existing guidelines and previous reviews of the field are based on a small fraction of published evidence. Therefore, we have performed a systematic search for randomized controlled trials evaluating racecadotril as add-on or in comparison to other treatments.

METHODS

A search was performed in PubMed, Scopus and Google Scholar without limits about country of origin or reporting language. A meta-analysis was conducted for the five most frequently used efficacy parameters.

RESULTS

We have retrieved 58 trials, from nine countries including six in comparison to placebo, 15 in comparison to various active treatments and 41 as add-on to various standard treatments (some multi-armed studies allowing more than one comparison). Trials used 45 distinct efficacy parameters, most often time to cure, % of cured children after 3 days of treatment, global efficacy and number of stools on second day of treatment. Racecadotril was superior to comparator treatments in outpatients and hospitalized patients with a high degree of consistency as confirmed by meta-analysis for the five most frequently used outcome parameters. For instance, it reduced time to cure from 106.2 h to 78.2 h (mean reduction 28.0 h; P < 0.0001 in 24 studies reporting on this parameter). Tolerability of racecadotril was comparable to that of placebo (10.4% vs. 10.6% adverse events incidence) or that of active comparator treatments other than loperamide (2.4% in both groups).

CONCLUSIONS

Based on a comprehensive review of the existing evidence, we conclude that racecadotril is more efficacious than other treatments except for loperamide and has a tolerability similar to placebo and better than loperamide. These findings support the use of racecadotril in the treatment of acute diarrhea in children.

[Consensus paper treatment of acute traveler's diarrhea. Practice recommendation for travel advice]

BACKGROUND

In times of mass tourism, traveler's diarrhea is one of the most common health problems of long-distance travel. Globally, some 40 million cases occur annually. Travellers to risk areas should therefore be comprehensively advised beforehand, as to what action to take in case of an acute traveler's diarrhea and what drugs to add to their first-aid kit. To date none, or hardly any specific studies or valid specific guidelines for the treatment of traveler's diarrhea are available for Germany.

METHOD

Drafting a consensus paper based on results of a specialists' meeting to evaluate therapeutic options in the treatment of acute uncomplicated travelers' diarrhea. The foundation for the present consensus recommendations is current evidence on antidiarrheals available in Germany for symptomatic treatment of gastrointestinal infections, summarized in the S2k guideline for gastrointestinal infections and Whipple's disease. Further taken into account for the present consensus recommendations were Pubmed-listed publications on symptomatic treatment of traveler's diarrhea, practical aspects, and the experts' experience in travel medicine.

RESULTS AND CONCLUSION

For the treatment of acute uncomplicated traveler's diarrhea - more than 90 % of all cases - the secretion inhibitor racecadotril is considered first choice, based on our evaluation criteria. The previously usual practice of recommending the antimotility drug loperamide as first choice should be reconsidered, in favor of the recent active ingredient racecadotril. Antibiotics should be used only in complicated cases. A large number of travelers who generally demand antibiotic therapy should be disabused of their expectations. Other therapeutic measures that are currently available for the treatment of acute diarrhea while traveling play a subordinate role.

Long-term neprilysin inhibition - implications for ARNIs

Neprilysin has a major role in both the generation and degradation of bioactive peptides. LCZ696 (valsartan/sacubitril, Entresto), the first of the new ARNI (dual-acting angiotensin-receptor-neprilysin inhibitor) drug class, contains equimolar amounts of valsartan, an angiotensin-receptor blocker, and sacubitril, a prodrug for the neprilysin inhibitor LBQ657. LCZ696 reduced blood pressure more than valsartan alone in patients with hypertension. In the PARADIGM-HF study, LCZ696 was superior to the angiotensin-converting enzyme inhibitor enalapril for the treatment of heart failure with reduced ejection fraction, and LCZ696 was approved by the FDA for this purpose in 2015. This approval was the first for chronic neprilysin inhibition. The many peptides metabolized by neprilysin suggest many potential consequences of chronic neprilysin inhibitor therapy, both beneficial and adverse. Moreover, LBQ657 might inhibit enzymes other than neprilysin. Chronic neprilysin inhibition might have an effect on angio-oedema, bronchial reactivity, inflammation, and cancer, and might predispose to polyneuropathy. Additionally, inhibition of neprilysin metabolism of amyloid-β peptides might have an effect on Alzheimer disease, age-related macular degeneration, and cerebral amyloid angiopathy. Much of the evidence for possible adverse consequences of chronic neprilysin inhibition comes from studies in animal models, and the relevance of this evidence to humans is unknown. This Review summarizes current knowledge of neprilysin function and possible consequences of chronic neprilysin inhibition that indicate a need for vigilance in the use of neprilysin inhibitor therapy.

A Comprehensive Comparison of the Efficacy and Tolerability of Racecadotril with Other Treatments of Acute Diarrhea in Adults

Racecadotril is a guideline-recommended treatment to alleviate symptoms of acute diarrhea. A systematic review of randomized studies was performed comparing efficacy and safety of treatment with racecadotril to that with placebo or active treatments in adults. In five double-blind studies, racecadotril and placebo had comparable tolerability, but racecadotril was more effective. This was consistent across multiple efficacy parameters including duration of diarrhea, number of diarrheic stools, abdominal pain, and meteorism; it was also consistent across countries in Africa, Asia, and Europe. In six randomized studies in outpatients comparing racecadotril to loperamide, resolution of symptoms occurred with similar speed and efficacy; however, racecadotril treatment was associated with less rebound constipation and less abdominal discomfort. The seventh comparative study performed in geriatric nursing home residents reported a superior efficacy of racecadotril. In direct comparison with Saccharomyces boulardii treatment, racecadotril exhibited similar tolerability but was more efficacious. One study compared racecadotril to octreotide in patients with acute diarrhea requiring hospitalization, rehydration, and antibiotic treatment; in this cohort, octreotide was more efficacious than racecadotril. In conclusion, in adults with acute diarrhea, racecadotril is more efficacious than placebo or S. boulardii, similarly efficacious as loperamide and, in patients with moderate to severe disease as add-on to antibiotics, less than octreotide. The tolerability of racecadotril is similar to that of placebo or S. boulardii and better than that of loperamide, particularly with regard to risk of rebound constipation. Taken together, these data demonstrate that racecadotril is a suitable treatment to alleviate symptoms of acute diarrhea in adults.

Opioid Facilitation of β-Adrenergic Blockade: A New Pharmacological Condition?

Recently, propranolol was suggested to prevent hyperlactatemia in a child with hypovolemic shock through β-adrenergic blockade. Though it is a known inhibitor of glycolysis, propranolol, outside this observation, has never been reported to fully protect against lactate overproduction. On the other hand, literature evidence exists for a cross-talk between β-adrenergic receptors (protein targets of propranolol) and δ-opioid receptor. In this literature context, it is hypothesized here that anti-diarrheic racecadotril (a pro-drug of thiorphan, an inhibitor of enkephalinases), which, in the cited observation, was co-administered with propranolol, might have facilitated the β-blocker-driven inhibition of glycolysis and resulting lactate production. The opioid-facilitated β-adrenergic blockade would be essentially additivity or even synergism putatively existing between antagonism of β-adrenergic receptors and agonism of δ-opioid receptor in lowering cellular cAMP and dependent functions.

Secretory diarrhoea: mechanisms and emerging therapies

Diarrhoeal disease remains a major health burden worldwide. Secretory diarrhoeas are caused by certain bacterial and viral infections, inflammatory processes, drugs and genetic disorders. Fluid secretion across the intestinal epithelium in secretory diarrhoeas involves multiple ion and solute transporters, as well as activation of cyclic nucleotide and Ca(2+) signalling pathways. In many secretory diarrhoeas, activation of Cl(-) channels in the apical membrane of enterocytes, including the cystic fibrosis transmembrane conductance regulator and Ca(2+)-activated Cl(-) channels, increases fluid secretion, while inhibition of Na(+) transport reduces fluid absorption. Current treatment of diarrhoea includes replacement of fluid and electrolyte losses using oral rehydration solutions, and drugs targeting intestinal motility or fluid secretion. Therapeutics in the development pipeline target intestinal ion channels and transporters, regulatory proteins and cell surface receptors. This Review describes pathogenic mechanisms of secretory diarrhoea, current and emerging therapeutics, and the challenges in developing antidiarrhoeal therapeutics.

Anti-rotavirus protein reduces stool output in infants with diarrhea: a randomized placebo-controlled trial

BACKGROUND & AIMS

Rotavirus infection is a leading cause of morbidity and mortality in children younger than 5 years of age. Current treatment options are limited. We assessed the efficacy of a llama-derived, heavy-chain antibody fragment called anti-rotavirus protein (ARP1), in modifying the severity and duration of diarrhea in male infants with rotavirus infection.

METHODS

We performed a double-blind, placebo-controlled trial of 176 male infants (6-24 months old) with severe rotavirus-associated diarrhea at Dhaka Hospital, Bangladesh. The infants were randomly assigned to groups given oral ARP1 (15-30 mg/kg/day, n = 88) or placebo (maltodextrin, n = 88) for a maximum of 5 days. The primary outcomes were severity (stool output) and duration of diarrhea and fecal excretion of rotavirus. Secondary outcomes were intake of oral rehydration salt solution, severity of vomiting, and serum levels of rotavirus-specific IgA.

RESULTS

In infants with only rotavirus infection, total cumulative stool output was 305.47 g/kg body weight among those given placebo (n = 63) and 237.03 g/kg body weight among those given ARP1 (n = 61) (a difference of 68.44 g/kg body weight or 22.5%; 95% confidence interval: 18.27-118.59 g/kg body weight; P =.0079). There was a significant reduction in rate of stool output (g/kg/d) in the ARP1 group compared with the placebo group (61%; P = .002). ARP1 had no significant effect in infants with concomitant infections or on any other measured outcomes. No adverse events could be linked to ARP1.

CONCLUSIONS

In a placebo-controlled trial, ARP1 reduced stool output in male infants with severe rotavirus-associated diarrhea. Clinicaltrials.gov number: NCT01259765.

Agents that act luminally to treat diarrhoea and constipation

Diarrhoea and constipation are common clinical complaints that negatively affect quality of life, reduce work productivity and lead to considerable health-care expenditure. A variety of therapies have been used to treat these conditions. Unlike drugs that require systemic absorption to exert their effects, luminally acting agents improve diarrhoea and constipation by altering intestinal and/or colonic motility, as well as mucosal absorption and secretion, through a variety of mechanisms. Examples of luminally acting agents for diarrhoea include peripherally acting opiate analogues, enkephalinase inhibitors, bile-acid binding agents, nonabsorbed antibiotics, probiotics, bismuth-containing compounds, berberine and agents with possible effects on intestinal secretion or permeability. Luminally acting drugs for constipation include bulking agents, surfactants, osmotics, stimulants, chloride-channel activators, probiotics, drugs that increase delivery of bile acids to the colon and natural therapies such as prunes and hemp seed extract. As the physiological effects of luminally acting drugs are largely confined to the gastrointestinal tract, these agents are unlikely to cause adverse effects outside of the gastrointestinal tract.

A comprehensive review of the pharmacodynamics, pharmacokinetics, and clinical effects of the neutral endopeptidase inhibitor racecadotril

Racecadotril, via its active metabolite thiorphan, is an inhibitor of the enzyme neutral endopeptidase (NEP, EC 3.4.24.11), thereby increasing exposure to NEP substrates including enkephalins and atrial natriuretic peptide (ANP). Upon oral administration racecadotril is rapidly and effectively converted into the active metabolite thiorphan, which does not cross the blood–brain-barrier. Racecadotril has mainly been tested in animal models and patients of three therapeutic areas. As an analgesic the effects of racecadotril across animal models were inconsistent. In cardiovascular diseases such as hypertension or congestive heart failure results from animal studies were promising, probably related to increased exposure to ANP, but clinical results have not shown substantial therapeutic benefit over existing treatment options in cardiovascular disease. In contrast, racecadotril was consistently effective in animal models and patients with various forms of acute diarrhea by inhibiting pathologic (but not basal) secretion from the gut without changing gastro-intestinal transit time or motility. This included studies in both adults and children. In direct comparative studies with loperamide in adults and children, racecadotril was at least as effective but exhibited fewer adverse events in most studies, particularly less rebound constipation. Several guidelines recommend the use of racecadotril as addition to oral rehydration treatment in children with acute diarrhea.

Use of racecadotril as outpatient treatment for acute gastroenteritis: a prospective, randomized, parallel study

OBJECTIVE

To compare the efficacy of therapy with racecadotril plus oral rehydration versus oral rehydration alone in children with gastroenteritis in an outpatient setting care.

STUDY DESIGN

Prospective, randomized, open and parallel study performed in a Pediatric Emergency Service of a tertiary care hospital. The study included 189 patients, ages 3 to 36 months, with acute gastroenteritis: 94 were administered an oral rehydration solution (OR), 94 received oral rehydration solution plus racecadotril (OR + R). The principal variable studied was the number of bowel movements in 48 hours after initiating treatment.

RESULTS

The groups were comparable clinically and epidemiologically at enrollment. No significant differences were found in the number of bowel movements between the 2 groups 48 hours after initiating treatment (4.1 +/- 2.7 bowel movements in the OR group vs 3.8 +/- 2.4 bowel movements in the OR + R group). No differences were found in the average duration of gastroenteritis (4.7 +/- 2.2 days in the OR group, 4.0 +/- 2.1 days in the OR + R group; P = .15). The incidence of adverse events was similar in both groups (19 patients [20.2%] in the OR group, 18 patients [19.1%] in the OR + R group).

CONCLUSIONS

In our study group, the use of racecadotril did not improve the symptoms of diarrhea compared with standard rehydration therapy.

[Systematic review of the efficacy of racecadotril in the treatment of acute diarrhoea]

OBJECTIVE

To estimate, through a systematic review of the literature, the efficacy of racecadotril in the treatment of acute diarrhoea.

MATERIAL AND METHODS

Randomised trials carried out in children comparing racecadotril with placebo in terms of diarrhoea recovery, stools output and adverse effects were selected. Electronic databases (Medline, EMBASE, CENTRAL, CINAHL, mRCT, Pascal) and bibliographies of retrieved articles were searched, and the drug developer was contacted. Two authors independently assessed the quality of the retrieved articles and extracted the data.

RESULTS

Two small sample size randomised trials (135 and 172 children) of moderate quality were selected. They included children with less than five days diarrhoea and aged between 3 months and 4 years. There was no difference in the proportion of children who recovered by day 5 (RR=0.73, CI 95% 0.29 to 1.81), although the stools volume during the first 48 hours was less in the racecadotril group (SMD=-0.65, CI 95% -0.88 to -0.52). There is no difference in the risk of vomiting (RR=1.16, CI 95% 0.64 to 2.12).

CONCLUSION

The proportion of recoveries by the 5th day is the same, although the stool volumes during the first 48 hours are less in the racecadotril treated children. It would be interesting to study the efficacy in a primary care setting assessing the cure rate, the stool volumes and the admission rate to elucidate if there is room for this drug.

Severe acute diarrhea

Acute diarrhea is commonly caused by an infection. Severe acute diarrhea warrants immediate medical evaluation and hospitalization. Indications for stool studies include fever; bloody diarrhea; recent travel to an endemic area; recent antibiotics; immunosuppression; and occupational risks, such as food handlers. Noninfectious causes include inflammatory bowel disease, radiation enteritis, and intestinal ischemia. Management of severe acute diarrhea includes intravenous fluid rehydration and empiric antibiotics. Use of antidiarrheal agents is controversial when invasive pathogens are suspected.

Treatment of infectious diarrhea in children

Diarrheal diseases remain an important cause of childhood morbidity and death in developing countries, although diarrheal deaths have significantly declined in recent years, mostly due to successes in the implementation of oral rehydration therapy (ORT), which is the principal treatment modality. Diarrhea may occur for varied reasons; however, most episodes of diarrhea in developing countries are infectious in origin. Three clinical forms of diarrhea (acute watery diarrhea, invasive diarrhea, and persistent diarrhea) have been identified to formulate a management plan. Acute diarrhea may be watery (where features of dehydration are prominent) or dysenteric (where stools contain blood and mucus). Rehydration therapy is the key to management of acute watery diarrhea, whereas antimicrobial agents play a vital role in the management of acute invasive diarrhea, particularly shigellosis and amebiasis. In persistent diarrhea, nutritional therapy, including dietary manipulations, is a very important aspect in its management, in addition to rehydration therapy. Rehydration may be carried out either by the oral or intravenous route, depending upon the degree of dehydration. Oral rehydration salts (ORS) solution (World Health Organization formula) is recommended for ORT. Intravenous fluid is recommended for initial management of severe dehydration due to diarrhea, followed by ORT with ORS solution for correction of ongoing fluid losses. Antimicrobial therapy is beneficial for cholera and shigellosis. Antiparasitic agents are indicated only if amebiasis and giardiasis are present. Appropriate feeding during diarrhea is recommended for nutritional recovery and to prevent bodyweight loss. Antidiarrheal agents do not provide additional benefit in the management of infectious diarrhea. Although some probiotics have been shown to be beneficial in the treatment of acute diarrhea due to rotavirus, their use in the treatment of diarrhea is yet to be recommended, even in developed countries. The children of developing countries might benefit from zinc supplementation during the diarrheal illness, but its mode of delivery and cost effectiveness are yet to be decided.

Getting control of intestinal secretion: thoughts for 2003

There has been a search for more than 20 years for agents that will directly inhibit intestinal secretory mechanisms and thereby reduce stool volume in patients with high volume watery diarrhoea. Recent work has highlighted the importance of neurohumoral mechanisms in the pathogenesis of diarrhoea, notably the role of 5-hydroxytryptamine, substance P, vasoactive intestinal polypeptide and neural reflexes within the enteric nervous system. Cholera toxin and Escherichia coli enterotoxins are known to invoke these mechanisms in some diarrhoeal states. This new dimension of intestinal pathophysiology has suggested possible novel targets for anti-secretory therapy including, 5-hydroxytryptamine receptor antagonists, substance P antagonists, vasoactive intestinal polypeptide antagonists and the possibility for potentiating the pro-absorptive effects of endogenous enkephalins by use of enkephalinase inhibitors. There now seems to be a real possibility that anti-secretory therapy will become more widely available in the future.

I, 3. The enteric nervous system and infectious diarrhea

This chapter discusses the background knowledge about the enteric nervous system (ENS) as well as the role of ENS in secretory states of the small intestine. The chapter describes the anatomy and physiology of the ENS. A description of the experimental evidence for the involvement of ENS in secretory states of the gut, primarily in cholera toxin-induced secretion that is the most thoroughly investigated secretory state, is presented in the chapter. The chapter focuses on the involvement of ENS in rotavirus (RV) diarrhea. The involvement of the ENS in diarrhea pathophysiology opens up new potential sites of action for drugs in the treatment of intestinal secretory states. The chapter concludes with a discussion of the sites of action for the pharmacological treatment of diarrhea.

[Effect of racecadotril in the management of acute diarrhea in infants and children]

BACKGROUND

The treatment of diarrhoea relies on the maintenance or restoration of hydration with maintenance of an adequate nutritional intake. Racecadotril has been shown to reduce the stools output during acute diarrhoea. The present work was aimed at measuring the number of emergency department visits for acute diarrhoea either the children received racecadotril or not.

METHOD

Racecadotril and rehydration were compared with rehydration alone in children aged three months to three years who had acute diarrhoea and were evaluated in the emergency department (ED). The primary end point was the number of medical exams during the week after starting treatment. Secondary end points were the number of stools during the first 48 hours, the duration of the diarrhoea and the weight on day 7.

RESULTS

One hundred and sixty-six children were alternatively randomized to the treated and the control groups. There was no difference for age, degree of dehydration and length of illness before the first visit between the groups. Whatever type of rehydration (oral or i.v.), the treated group had a significant lower number of stools (p < 0.001) and a faster recovery (p < 10(-9)). The children receiving racecadotril needed less additional ED visits for the same episode (p < 0.05). There was no difference for the weight-gain on day 7.

CONCLUSIONS

This study demonstrates the efficacy of racecadotril as adjuvant therapy to oral and i.v. rehydration in the treatment of acute diarrhoea and a fewer emergency department second visit before recovery.

Efficacy and tolerability of racecadotril in acute diarrhea in children

BACKGROUND & AIMS

Oral rehydration therapy is the only treatment recommended by the World Health Organization in acute diarrhea in children. Antisecretory drugs available could not be used because of their side effects, except for racecadotril, which is efficient in acute diarrhea in adults.

METHODS

The efficacy and tolerability of racecadotril (1.5 mg/kg administered orally 3 times daily) as adjuvant therapy to oral rehydration were compared with those of placebo in 172 infants aged 3 months to 4 years (mean age, 12.8 months) who had acute diarrhea. The treatment groups were comparable in terms of age, duration of diarrhea, number of stools, and causative microorganism at inclusion.

RESULTS

During the first 48 hours of treatment, patients receiving racecadotril had a significantly lower stool output (grams per hour) than those receiving placebo. The 95% confidence interval was 43%-88% for the full data set (n = 166; P = 0.009) and 33%-75% for the per-protocol population (n = 116; P = 0.001). There was no difference between treatments depending on rotavirus status. Significant differences between treatment groups were also found after 24 hours of treatment: full data set (n = 167; P = 0.026) and per-protocol population (n = 121; P = 0.015). Tolerability was good in both groups of patients.

CONCLUSIONS

This study demonstrates the efficacy (up to 50% reduction in stool output) and tolerability of racecadotril as adjuvant therapy to oral rehydration solution in the treatment of severe diarrhea in infants and children.

Role of the neuroendocrine system in pathogenesis of gastroenteritis

The concept of neuroendocrine modulation of infectious gastroenteritis adds another dimension to the pathophysiology of diarrhoeal diseases. Furthermore it opens up new avenues for therapeutic intervention. Until now, most interest has been directed at enterotoxin-producing bacteria, notably Vibrio cholerae and the enterotoxigenic Escherichia coli. However, more recently neuroendocrine recruitment has been implicated by other pathogens. The roles of vasoactive intestinal peptide, 5-hydroxytryptamine, tachykinins, nitric oxide and opioids are explored in this review. In addition new insights in the contradictory galanin story are discussed.

An overview of clinical studies with racecadotril in adults

Since preclinical studies had indicated the potential efficacy and tolerability of racecadotril for the treatment of diarrhoea in man, a series of studies was carried out to assess the clinical effects of racecadotril. These studies were also designed to evaluate whether racecadotril possessed the clinical properties that had been previously identified for an ideal agent to treat infectious diarrhoea. The pure antisecretory action of racecadotril was confirmed in these clinical studies, as was the drug's rapid onset of action. The high therapeutic index of racecadotril was combined with a lack of effect on the central nervous system. Finally, racecadotril was found to be effective in treating acute diarrhoea in double-blind studies against both placebo and the mu opiate receptor agonist, loperamide. The efficacy of racecadotril in acute diarrhoea was not associated with adverse gastrointestinal effects, and its adverse events profile was similar to that of placebo. It was concluded that racecadotril offers a new approach to the treatment of diarrhoea via its mechanism of action as a true antisecretory agent.

Racecadotril demonstrates intestinal antisecretory activity in vivo

BACKGROUND

Racecadotril (acetorphan), a potent enkephalinase inhibitor, protects endogenous enkephalins from degradation. Racecadotril exhibits experimental and clinical antidiarrhoeal activity without any effect on intestinal motility, suggesting selective antisecretory activity. The antisecretory effect of racecadotril was directly assessed in the present study.

METHODS

A 1 m, jejunal, Thiry-Vella loop was created in six mongrel dogs, and water and ionic fluxes were evaluated during infusion (2 mL/min) of Tyrode solution labelled with 14C-polyethylene glycol. Fluxes were determined both in the basal state and 5-6 h after commencement of a 2-h infusion of cholera toxin (0.4 microgram/mL). Racecadotril (10 mg/kg) or vehicle was given orally with and without prior intravenous administration of naloxone (0.1 mg/kg) or phentolamine (0.2 mg/kg).

RESULTS

Basal absorption remained unchanged following racecadotril administration; however, racecadotril significantly decreased (P = 0.01) cholera toxin-induced water, sodium, and potassium hypersecretion, from 0.73 +/- 0.15 to 0.37 +/- 0.13 mL/min; from 125.0 +/- 16.1 to 14.7 +/- 9.5 microMol/min; and from 3.41 +/- 0.66 to 1.66 +/- 0.61 microMol/min, respectively. This antisecretory activity of racecadotril was suppressed by naloxone but not by phentolamine.

CONCLUSIONS

This study directly demonstrates the antisecretory activity of racecadotril in relation to the protection of endogenous enkephalins.

Comparison of racecadotril and loperamide in adults with acute diarrhoea

METHODS

A multicentre, randomized, double-blind, double-placebo, parallel-group study was carried out to compare the efficacy, tolerability, and safety of racecadotril (100 mg three times daily) and loperamide (2 mg after each diarrhoeic stool) in 157 adults with acute diarrhoea. Patients were treated for 7 days or until recovery, if this took place earlier.

RESULTS

Both groups of patients passed similar numbers (mean +/- S.E.M.) of stools before recovery (3.5 +/- 0.5 for racecadotril vs. 2.9 +/- 0.4 for loperamide), and the duration of diarrhoea (mean +/- S.E.M.) was similar in both groups (14.9 +/- 2.0 h for racecadotril and 13.7 +/- 2.2 h for loperamide). Both treatments reduced the incidence of associated symptoms and signs during the study, and both were similarly well tolerated. However, more patients on loperamide reported rebound constipation during treatment (18.7% vs. 9.8% with racecadotril).

CONCLUSIONS

The enkephalinase inhibitor, racecadotril, and the intestinal transit inhibitor, loperamide, were similarly and rapidly effective in resolving the symptoms and associated signs of diarrhoea.