Therapeutic approach to the patient with irritable bowel syndrome

Effects of the Tibetan herbal formula Padma Lax on visceral nociception and contractility of longitudinal smooth muscle in a rat model

BACKGROUND

The high prevalence of functional bowel disorders among the general population contrasts with the limited number of pharmacological treatment options for this condition. This has led to an interest for alternative therapeutic approaches. Padma Lax is an herbal laxative on the basis of Tibetan formulas. Our aim is to examine the effect of Padma Lax on visceral nociception in vivo and (B) on contractile activity of longitudinal smooth muscle of the lower gut in vitro and ex vivo.

METHODS

(A) Visceral sensory function in response to colorectal distension was assessed by abdominal wall electromyography in male Wistar rats pretreated with Padma Lax. (B) Effects of Padma Lax on contractility of gut smooth muscles were studied both in vitro with superfusion of the agent and ex vivo following oral administration of the preparation. Activities were measured as area under the curve.

KEY RESULTS

(A) For visceral sensitivity, no differences were observed between the Padma Lax and the control group. (B) Proximal colon muscle strips of the Padma Lax pretreated group showed significantly lower spontaneous contractility ex vivo than controls. Cholinergic procontractile stimulation was reduced in Padma Lax pretreated group and in colon strips of naive rats when Padma Lax was superfused in vitro (all P < 0.05).

CONCLUSION & INFERENCES

Cholinergic mechanisms appear to be important in the modulation of rat proximal colon contractility of orally and directly applied Padma Lax. These findings help elucidate a potential mechanism of action of this herbal remedy which has undergone clinical testing in patients with constipation predominant irritable bowel syndrome.

Colorectal distension-induced prefrontal cortex activation in the Wistar-Kyoto rat: implications for irritable bowel syndrome

The prefrontal cortex plays a key role in the perception of painful stimuli, including those emerging from the viscera. Colorectal distension is a non-invasive stimulus used to study visceral pain processing in the nervous system. Visceral hypersensitivity is one of the main characteristics of the functional bowel disorder irritable bowel syndrome (IBS). Moreover, recent human neuroimaging studies have emphasized the importance of altered brain activity and circuitry in the manifestation of IBS symptom severity and reaction to visceral stimuli. It is unclear whether animal models of visceral hypersensitivity display a similar response. Therefore, in the present study, we have used c-Fos protein immunoreactivity as an indicator of cell activation, to compare the response of the viscerally hypersensitive Wistar-Kyoto (WKY) rat and control Sprague-Dawley (SD) rat strains to colorectal distension (CRD), a noxious visceral stimulus. Several corticolimbic structures were analysed including the prelimbic cortex, infralimbic cortex and the rostral and caudal anterior cingulate cortices. Moreover, visceral hypersensitivity was also assessed behaviourally in both strains. As previously described WKY rats had a lower pain threshold than SD controls in response to CRD. In all brain regions analysed, exposure to CRD induced an increase in c-Fos activation in both the WKY and SD rats. However, an exaggerated cell activation was found in the prelimbic, infralimbic and rostral anterior cingulate cortices of the WKY rat compared to SD animals. No significant difference was found in caudal anterior cingulate cortex activation when the strains were compared. These results demonstrate, to our knowledge, for the first time an augmented colorectal distension-induced prefrontal cortex activity in WKY rats similar to that seen in IBS patients, further supporting the use of this strain as a model in which to study brain-gut axis dysregulation observed in IBS.

Irritable bowel syndrome: current approach to symptoms, evaluation, and treatment

There are frequent advances in knowledge about the clinical presentation, pathophysiology, and treatment of irritable bowel syndrome. It is important for clinicians to be aware of available therapies and the supporting evidence for those therapies to increase patient satisfaction. This is best achieved with a collaborative and long-term clinician-patient relationship and mutual commitment to modify therapy and try new modalities until the greatest relief of symptoms and improvement in health-related quality of life is achieved. This article reviews symptoms, comorbidities, gender differences, and measure of severity in irritable bowel syndrome and current and evidence-based approaches to evaluation and treatment, and the new symptom-based Rome III diagnostic criteria are reviewed and explained.

Health technology assessment and ill-structured problems: a case study concerning the drug mebeverine

OBJECTIVES

The practical significance of health technology assessment (HTA) in policy decisions or clinical practice has been challenged. Possibly, problem definitions underlying HTA do not concur sufficiently with the problem definitions held by policy makers or clinicians. We performed an in-depth case study on mebeverine, a drug prescribed to patients with irritable bowel syndrome, to explore this hypothesis.

METHODS

The theoretical framework was provided by the theory of argumentative policy analysis. We analyzed documents and held semistructured interviews to collect data. We reconstructed interpretative frames to analyze actors' argumentation.

RESULTS

The funding and usage problems relating to mebeverine were ill-structured. Actors disagreed on the information needed and the norms at stake. As a result, the problem definition shifted, and the resulting problem definitions failed to correspond with the problems perceived by the target populations.

CONCLUSIONS

To ensure that future studies on healthcare problems are useful, it is imperative that policy makers take the problem definitions of potential users into account.

The efficacy of an herbal medicine, Carmint, on the relief of abdominal pain and bloating in patients with irritable bowel syndrome: a pilot study

Carmint contains total extracts of Melissa officinalis, Mentha spicata, and Coriandrum sativum, which have antispasmodic, carminative, and sedative effects. As abdominal pain/discomfort and bloating are commonly observed in patients with irritable bowel syndrome, we decided to evaluate the effectiveness of Carmint in relieving these symptoms in irritable bowel syndrome patients. We randomly assigned 32 irritable bowel syndrome patients to receive either Carmint or placebo, plus Loperamide or psyllium (based on their predominant bowel function), for 8 weeks. T-test analysis of the results showed that the severity and frequency of abdominal pain/discomfort were significantly lower in the Carmint group than the placebo group at the end of the treatment (P=0.016 and P=0.001, respectively), as were the severity and frequency of bloating (P=0.02 and P=0.002, respectively). This pilot study suggests that Carmint plus loperamide or Carmint plus psyllium (depending on the irritable bowel syndrome subtype) might be effective in these patients.

Identification of cytochrome P450 isoforms involved in the metabolism of loperamide in human liver microsomes

OBJECTIVE

The purpose of the present study was to elucidate the cytochrome P450 (P450) isoform(s) involved in the metabolism of loperamide (LOP) to N-demethylated LOP (DLOP) in human liver microsomes.

METHODS

Three established approaches were used to identify the P450 isoforms responsible for LOP N-demethylation using human liver microsomes and cDNA-expressed P450 isoforms: (1) correlation of LOP N-demethylation activity with marker P450 activities in a panel of human liver microsomes, (2) inhibition of enzyme activity by P450-selective inhibitors, and (3) measurement of DLOP formation by cDNA-expressed P450 isoforms. The relative contribution of P450 isoforms involved in LOP N-demethylation in human liver microsomes were estimated by applying relative activity factor (RAF) values.

RESULTS

The formation rate of DLOP showed biphasic kinetics, suggesting the involvement of multiple P450 isoforms. Apparent Km and Vmax values were 21.1 microM and 122.3 pmol/min per milligram of protein for the high-affinity component and 83.9 microM and 412.0 pmol/min per milligram of protein for the low-affinity component, respectively. Of the cDNA-expressed P450 s tested, CYP2B6, CYP2C8, CYP2D6, and CYP3A4 catalyzed LOP N-demethylation. LOP N-demethylation was significantly inhibited when coincubated with quercetin (a CYP2C8 inhibitor) and ketoconazole (a CYP3A4 inhibitor) by 40 and 90%, respectively, but other chemical inhibitors tested showed weak or no significant inhibition. DLOP formation was highly correlated with CYP3A4-catalyzed midazolam 1-hydroxylation (rs=0.829; P<0.01), CYP2B6-catalzyed 7-ethoxy-4-trifluoromethylcoumarin O-deethylation (rs=0.691; P<0.05), and CYP2C8-catalyzed paclitaxel 6alpha-hydroxylation (rs=0.797; P<0.05).

CONCLUSION

CYP2B6, CYP2C8, CYP2D6, and CYP3A4 catalyze LOP N-demethylation in human liver microsomes, and among them, CYP2C8 and CYP3A4 may play a crucial role in LOP metabolism at the therapeutic concentrations of LOP. Coadministration of these P450 inhibitors may cause drug interactions with LOP. However, the clinical significance of potential interaction of LOP metabolism by CYP2C8 and CYP3A4 inhibitors should be studied further.

Users of oral steroids are at a reduced risk of developing irritable bowel syndrome

PURPOSE

To study whether irritable bowel syndrome (IBS) is associated with the use of oral steroids and whether there is a dose- or duration-response.

METHODS

We followed up a cohort of 65,270 patients aged 20-74 years old enrolled in the General Practice Research Database in the UK with at least one prescription for steroids between 1994 and 1999. We performed a nested case-control analysis to estimate the adjusted relative risk (RR) associated with the use of steroids using unconditional logistic regression. Cases were 466 patients with a first episode of IBS during follow-up and controls were 5000 individuals randomly selected from the study cohort.

RESULTS

Current users of oral steroids presented an RR of 0.6 (95% CI: 0.4-0.9) compared to non-users. Doses greater than 10 mg of prednisolone daily were associated with an RR of 0.4 (95% CI: 0.2-0.9). When we stratified by age, no reduced risk of IBS was apparent under the age of 40 years. The reduced risk of IBS was greater among females than males.

CONCLUSIONS

Our results suggest that oral steroids can reduce the risk of a diagnosis of IBS. The apparent effect modification of age and sex deserves further research.

Short-chain fatty acid enemas fail to decrease colonic hypersensitivity and inflammation in TNBS-induced colonic inflammation in rats

BACKGROUND AND AIMS

Short-chain fatty acid (SCFA) (especially butyrate) enemas are widely used to reduce symptoms associated with human inflammatory bowel disease. The purpose of this study was to evaluate their real effect on colonic sensitivity in rats.

METHODS

The effects of saline and SCFA enemas (acetate, propionate and particularly butyrate) were studied on visceral pain thresholds following colonic distension in control rats and in rats with colitis (instilled with trinitrobenzene sulfonic acid (TNBS)).

RESULTS

Butyrate enemas (40 mM twice daily for 14 days) decreased colonic pain thresholds in control rats; they did not reduce the TNBS-induced hypersensitivity, but on the contrary increased its duration (without modifying the inflammation score). This pronociceptive effect was confirmed in control rats receiving twice daily enemas of 80 mM for 3 days and two enemas of 240 mM of a butyrate solution. The other SCFA enemas did not modify the hypersensitivity of rats with colitis and induced proinflammatory effects.

CONCLUSIONS

The beneficial effect of SCFA (especially butyrate) enemas on hypersensitivity and inflammation in inflammatory bowel disease is questionable and needs to be thoroughly investigated in humans.

Irritable bowel syndrome. Diagnosis is based on clinical criteria

Irritable bowel syndrome is one of several functional bowel disorders. As the data about this common syndrome increase, so does the understanding that it is a disorder with complex pathophysiologic factors. In this article, Drs Morgan and Robson provide the latest information about IBS and its diagnosis and outline a strategy for cost-effective treatment and improved quality of life for patients with this disorder.

Alverine citrate fails to relieve the symptoms of irritable bowel syndrome: results of a double-blind, randomized, placebo-controlled trial

BACKGROUND

Alverine citrate has been used in the treatment of irritable bowel syndrome for many years.

AIMS

To compare the efficacy and safety of a new formulation of alverine citrate, a 120-mg capsule, with placebo given three times daily for 12 weeks.

METHODS

One hundred and seven patients with irritable bowel syndrome were entered into this three-centre, double-blind, randomized, placebo-controlled, parallel group trial. The primary end-point was relief of abdominal pain indicated by improvement in the scores for severity and frequency. Secondary efficacy variables included scores for other clinical symptoms and for overall well-being.

RESULTS

The severity and frequency of abdominal pain improved in 66% and 68% of patients treated with alverine citrate vs. 58% and 69% of the placebo group, but these differences were not significant. The mean percentage reduction in the scores for abdominal pain from baseline to the final assessment, although greater in the alverine citrate group (43.7%) compared with the placebo group (33.3%), was not statistically significant.

CONCLUSIONS

Alverine citrate is no better than placebo at relieving the symptoms of irritable bowel syndrome. Future trials should be designed to take into account the high and persistent placebo response seen in this condition.

Mechanical stimulation activates Galphaq signaling pathways and 5-hydroxytryptamine release from human carcinoid BON cells

5-Hydroxytryptamine (5-HT) released from enterochromaffin cells activates secretory and peristaltic reflexes necessary for lubrication and propulsion of intestinal luminal contents. The aim of this study was to identify mechanosensitive intracellular signaling pathways that regulate 5-HT release. Human carcinoid BON cells displayed 5-HT immunoreactivity associated with granules dispersed throughout the cells or at the borders. Mechanical stimulation by rotational shaking released 5-HT from BON cells or from guinea pig jejunum during neural blockade with tetrodotoxin. In streptolysin O-permeabilized cells, guanosine 5'-O- (2-thiodiphosphate) (GDP-beta-S) and a synthetic peptide derived from the COOH terminus of Galphaq abolished mechanically evoked 5-HT release, while the NH(2)-terminal peptide did not. An antisense phosphorothioated oligonucleotide targeted to a unique sequence of Galphaq abolished mechanically evoked 5-HT release and reduced Galphaq protein levels without affecting the expression of Galpha(11). Depletion and chelation of extracellular calcium did not alter mechanically evoked 5-HT release, whereas depletion of intracellular calcium stores by thapsigargin and chelation of intracellular calcium by 1,2-bis (o-Aminophenoxy) ethane-N,N,N',N'-tetraacetic acid tetra (acetoxymethyl) ester (BAPTA-AM) reduced 5-HT release. Mechanically evoked 5-HT release was inhibited by somatostatin-14 in a concentration-dependent manner. The results suggest that mechanical stimulation of enterochromaffin-derived BON cells directly or indirectly stimulates a G protein-coupled receptor that activates Galphaq, mobilizes intracellular calcium, and causes 5-HT release.

Psychologic Therapies for Irritable Bowel Syndrome

The treatment of patients with irritable bowel syndrome (IBS) is a difficult task, as the results from therapy with pharmacologic agents have been disappointing. Psychologic treatments, in particular cognitive behavior therapy, hypnotherapy, and dynamic psychotherapy have all shown to be effective in the treatment of patients with IBS. Underpinning all these treatments is a clear understanding of a biopsychosocial model of interaction between emotion and gut function in IBS. These psychologic therapies are intended to break the negative feedback loop between emotion and gut function in order to reduce symptoms. Attention to the psychologic issues underlying IBS helps reduce psychosocial factors that maintain the presence of symptoms and inappropriate health-care seeking behavior. There are a number of common elements in the psychologic approaches that can be used in routine clinical practice; these include a detailed assessment, psychoeducation, support, and reassurance.

Alosetron

Each month, subscribers to The Formulary® Monograph Service receive five to six researched monographs on drugs that are newly released or are in late Phase III trials. The monographs are targeted to your Pharmacy and Therapeutics Committee. Subscribers also receive monthly one-page summary monographs on the agents that are useful for agendas and pharmacy/nursing in-services. A comprehensive target drug utilization evaluation (DUE) is also provided each month. The monographs are published in printed form and on diskettes that allow customization. Subscribers to the The Formulary Monograph Service also receive access to a pharmacy bulletin board called The Formulary Information Exchange (The F.I.X). All topics pertinent to clinical pharmacy are discussed on The F.I.X.

Through the cooperation of The Formulary, Hospital Pharmacy publishes selected reviews in this column. If you would like information about The Formulary Monograph Service or The F.I.X., call The Formulary at 800-322-4349. The June 2000 Formulary monographs are on pantoprazole, oral and intravenous; meloxicam; zonisamide; gentuzum-ab zogamicin; and vertiporfin. The DUE is on meloxicam.