Limitations of indirect methods of estimating small bowel transit in man

What about clonidine for diarrhoea? A systematic review and meta-analysis of its effect in humans

BACKGROUND

Clonidine is considered an alternative treatment for refractory diarrhoea. The evidence in the literature is scarce and not conclusive. The present paper's purpose is to gather available evidence and provide a systematic answer regarding the effectiveness of clonidine for diarrhoea.

METHOD

We performed a systematic review of clonidine and its effect on diarrhoea. Meta-analysis was performed with a random effects model of the standardized mean difference (SMD) or the weighted mean difference and heterogeneity was quantified with I (2) and publication bias was assessed with Egger's and Begg's test. Subgroup analyses and meta-regression were performed to investigate sources of heterogeneity. Any empirical study describing use of clonidine for diarrhoea in humans independent of age was included. For the meta-analysis, papers had to provide sufficient data to produce an effect measure, while case reports were not included in the meta-analysis and are discussed narratively only.

RESULTS

A total of 24 trials and seven case reports were identified. Clonidine (median dose 300 μg/day) has been used for treatment of diarrhoea in irritable bowel syndrome, faecal incontinence, diabetes, withdrawal-associated diarrhoea, intestinal failure, neuroendocrine tumours and cholera; studies were also performed on healthy volunteers. Results indicate a strong effect of clonidine on diarrhoea (SMD = -1.02, 95% confidence interval [CI] -1.46 to -0.58) with a decrease of stool volume by 0.97 l/day, stool frequency by 0.4 times/day and increase in transit time by 31 minutes. In a sensitivity analysis of studies with functional diarrhoea and sample size over 10 subjects, the effect was similar -0.99 (95% CI -1.54 to -0.43). There is however significant heterogeneity and publication bias. Heterogeneity decreased in subgroup analyses by condition but not with other factors examined. A limitation of the present study includes small study effects.

CONCLUSION

Clonidine is effective for treatment of diarrhoea and should be considered as an alternative when all other medications have failed.

Evaluation of a three compartment in vitro gastrointestinal simulator dissolution apparatus to predict in vivo dissolution

In vitro dissolution tests are performed for new formulations to evaluate in vivo performance, which is affected by the change of gastrointestinal (GI) physiology, in the GI tract. Thus, those environmental changes should be introduced to an in vitro dissolution test. Many studies have successfully shown the improvement of in vitro-in vivo correlations (IVIVC) by introducing those physiological changes into dissolution tests. The gastrointestinal simulator (GIS), a multicompartment in vitro dissolution apparatus, was developed to evaluate in vivo drug dissolution. A gastric-emptying rate along with transit rate are key factors to evaluate in vivo drug dissolution and, hence, drug absorption. Dissolution tests with the GIS were performed with Biopharmaceutical Classification System class I drugs at five different gastric-emptying rates in the fasted state. Computational models were used to determine in vivo gastric-emptying time for propranolol and metoprolol based on the GIS dissolution results. Those were compared with published clinical data to determine the gastric half-emptying time. In conclusion, the GIS is a practical tool to assess dissolution properties and can improve IVIVC.

Initial evidence that GLP-1 receptor blockade fails to suppress postprandial satiety or promote food intake in humans

Glucagon-like peptide 1 (GLP-1) has incretin effects that are well-documented, but the independent role of GLP-1 action in human satiety perception is debated. We hypothesized that blockade of GLP-1 receptors would suppress postprandial satiety and increase voluntary food intake. After an overnight fast, eight normal weight participants (seven men, BMI 19-24.7 kg/m(2), age 19-29 year) were enrolled in a double-blind, placebo-controlled, randomized crossover study of the GLP-1 antagonist Exendin-[9-39] (Ex-9) to determine if the satiating effects of a meal are dependent on GLP-1 signaling in humans. Following a fasting blood draw, iv infusion of Ex-9 (600-750 pmol/kg/min) or saline began. Thirty minutes later, subjects consumed a standardized breakfast followed 90 min later (at the predicted time of maximal endogenous circulating GLP-1) by an ad libitum buffet meal to objectively measure satiety. Infusions ended once the buffet meal was complete. Visual analog scale ratings of hunger and fullness and serial assessments of plasma glucose, insulin, and GLP-1 concentrations were done throughout the experiment. Contrary to the hypothesis, during Ex-9 infusion subjects reported a greater decrease in hunger due to consumption of the breakfast (Ex-9 -62 ± 5; placebo -41 ± 9; P=0.01) than during placebo. There were no differences in ad libitum caloric intake between Ex-9 and placebo. Ex-9 increased glucose, insulin, and endogenous GLP-1, which may have counteracted any effects of Ex-9 infusion to block satiety signaling. Blockade of GLP-1 receptors failed to suppress subjective satiety following a standardized meal or increase voluntary food intake in healthy, normal-weight subjects.

13C breath tests: visions and realities

Breath tests have been used in research laboratories for over 25 y. Originally, the tests were based on the use of (14)C, rather than on the nonradioactive isotope, (13)C. When (13)C became widely available at a reasonable cost, research groups in the United States and Europe developed methodologies to measure (13)C abundance in samples of CO(2). The tests used a variety of substrates and measured pancreatic function, fat absorption, bacterial overgrowth and P(450) mixed-function oxidase. Thus far, the only test to be approved by the Food and Drug Administration is the (13)C-urea breath test. This manuscript describes the process by which approval is gained, and indicates the steps necessary for other tests to receive Food and Drug Administration approval.

The X-ray contrast medium iodixanol detects increased colonic permeability equally well as 51Cr-labeled ethylenediaminetetraacetic acid in experimental colitis of rats

BACKGROUND

Non-ionic, water-soluble radiographic contrast media have been suggested as intestinal permeability probes. We studied the permeability of the isosmolar contrast medium iodixanol and 51Cr-labeled ethylenediaminetetraacetic acid (EDTA) from the non-perforated colon after induction of colonic inflammation.

METHODS

Colonic inflammation and ulcerations were induced by luminal colonic instillation of trinitrobenzenesulfonic acid, dissolved in 40% ethanol. Controls received saline. Fourteen days later iodixanol, 320 mg I/ml, and 51Cr-EDTA were given as an enema. Urine was collected for the subsequent 6 h and subjected to high-performance liquid chromatography and gamma activity counting.

RESULTS

Urinary recovery of iodixanol and 51Cr-EDTA increased gradually with severity of the colonic inflammation. The correlation between iodixanol and 51Cr-EDTA recovery was strong (corr.coeff = 0.97).

CONCLUSIONS

Iodixanol shows as good properties as 51Cr-EDTA when used as intestinal permeability probe in the inflamed and ulcerated rat colon. Use of the radiopaque properties of iodixanol enable intestinal probe exposure registration by film or fluoroscopy.

Increased intestinal permeability for the isosmolar contrast medium iodixanol during small-bowel ischaemia in rats

BACKGROUND

Intestinal ischaemia may be difficult to recognize in the early stages. Increased urinary recovery of water-soluble contrast medium during and intestinal follow-through has been suggested as a sign of bowel ischaemia.

METHODS

Urinary excretion of the isosmolar water-soluble X-ray contrast medium iodixanol was measured after instillation via an orogastric tube in 56 rats with occlusion of the mesenteric blood vessels.

RESULTS

Mesenteric venous occlusion caused only minor histologic alterations of the mucosa. High-performance liquid chromatography (HPLC) and X-ray fluorescence analysis measured urinary iodixanol concentrations 10 and 13 times higher than in the groups with mesenteric arterial occlusion than in controls (p < 0.001), and 3 and 4 times higher than in the group with venous occlusion (p < or = 0.05). Correlation between HPLC and X-ray fluorescence measurements of contrast medium in urine was strong (r = 0.98).

CONCLUSION

Measuring urinary contrast medium levels during intestinal follow-through may aid in distinguishing bowel ischaemia following mesenteric arterial occlusion from mesenteric venous occlusion and from the normal bowel.

Intestinal permeability measurements - a new application for water soluble contrast media?

The detection and quantification of altered intestinal barrier function (intestinal permeability) have been addressed frequently during the last year, but the tests available for determination of intestinal permeability are both flawed and have limitations. The new water-soluble roentgen contrast media (CM) of low- and iso-osmolar type have been proposed as intestinal permeability probes. In this article this possible new application for water-soluble CM is discussed in terms of their inherent properties and the experimental and clinical results obtained so far. The 2 iso-osmolar dimers, iodixanol (Visipaque) and iotrolan (Isovist), seem to be as good as the well-documented radio-labeled permeability probe (51)Cr-EDTA in detecting injury of the intestinal mucosal barrier. The CM offer the advantage of allowing direct control of bowel wall exposure with the aid of fluoroscopy. Current permeability probes lack this quality. Iodine-containing substances may be analyzed by the rapid, simple and reliable X-ray fluorescence technique, which is suitable for application in routine clinical practice. We conclude that the new water-soluble roentgen CM have properties which may be of use in the diagnosis and quantification of altered intestinal barrier function.

Lactulose hydrogen breath test in orocecal transit assessment. Critical evaluation by means of scintigraphic method

Orocecal transit time can be studied easily using the hydrogen breath test with lactulose, but the method has some important limitations. The orocecal transit time of 10 patients suffering from irritable bowel syndrome was measured twice, at a one-week interval, by breath test and scintigraphy simultaneously using an aqueous solution of 20 g lactulose containing 74 MBq of [99mTc]DTPA. Abdominal radioactivity and alveolar hydrogen values obtained every 5 min were noted and used to obtain the following: orocecal transit time by the two methods; ileocecal lactulose flow; total and per gram of lactulose hydrogen production; mean hydrogen concentration during the right colon filling; and measurement error of the breath test with respect to the scintigraphy. In the case of the breath test, the orocecal transit time intrapatient reproducibility was better (coefficient of variation = 13.5%) when a hydrogen threshold increment of 5 ppm was used; the best correlation with the scintigraphic measurement was observed at this threshold (r = 0.90, P < 0.001). The breath test overestimated orocecal transit time with the error correlating negatively and significantly with the total hydrogen production and, particularly, the mean hydrogen concentration (r = 0.79, P < 0.01): for a mean hydrogen concentration of more than 15 ppm, the error was negligible, while within this value there was a noticeable overestimation. To conclude, the lactulose hydrogen breath test is capable of giving an accurate measurement of orocecal transit time if a hydrogen threshold increment of 5 ppm is chosen and if the mean hydrogen concentration in the first 30 min of the right colon filling is taken into account.

Effects of acetorphan, an enkephalinase inhibitor, on experimental and acute diarrhoea

Acetorphan is an orally active inhibitor of enkephalinase (EC 3.4.24.11) with antidiarrhoeal activity in rodents apparently through protection of endogenous enkephalins and a purely antisecretory mechanism. Its antidiarrhoeal activity in man was assessed in an experimental model of cathartic induced secretory diarrhoea as well as in acute diarrhoea of presumed infectious origin. In six healthy volunteers receiving castor oil and pretreated with acetorphan or placebo in a crossover controlled trial, the drug significantly decreased the number and weight of stools passed during 24 hours. About 200 outpatients with severe acute diarrhoea (more than five stools per day) were included in a randomised double blind study of acetorphan against placebo. The significant antidiarrhoeal activity of acetorphan was established using a variety of criteria: (i) the duration of both diarrhoea and treatment were diminished; (ii) no acetorphan treated patient withdrew from the study whereas five dropped out because of worsening in the placebo group; (iii) the frequency of symptoms associated with diarrhoea--for example, abdominal pain or distension, nausea and anorexia--remaining after two weeks was nearly halved; (iv) using visual analogue scales acetorphan treatment was found more effective than placebo by both investigators and patients. There was statistically no significant difference between acetorphan and placebo in respect of side effects, particularly constipation, which often accompanies the antidiarrhoeal activity of mu opioid receptor agonists this difference is attributable to the lack of antipropulsive activity of acetorphan in man. The efficacy and tolerance of acetorphan suggest that enkephalinase inhibition may represent a novel therapeutic approach for the symptomatic management of acute secretory diarrhoea without impairing intestinal transit.

Metabolism of ursocholic acid in humans: conversion of ursocholic acid to deoxycholic acid

To study the metabolism of ursocholic acid, control subjects were injected with radiolabeled cholic and ursocholic acids before and after 1 wk of 900 mg/day oral ursocholic acid. Daily samples of bile were obtained, and biliary bile acids were extracted and purified to determine bile acid kinetics. During ursocholic acid therapy ursocholic acid became the principal bile acid (35% +/- 3% of total bile acids, mean +/- S.E.M.), and the percentage of biliary cholic and chenodeoxycholic acids decreased (p less than 0.05). Cholic acid production fell from 190 +/- 15 mg/day to 135 +/- 20 mg/day (p = 0.078). The total bile acid pool was increased twofold (p less than 0.05), whereas the deoxycholic acid pool was enlarged from 440 +/- 170 mg to 1,175 +/- 90 mg (p less than 0.02). As much as 28% of the fed ursocholic acid was excreted in the urine, 85% as the free acid and 15% as the glycine conjugate. During treatment, ursocholic acid became the source for 69% +/- 11% of biliary deoxycholic acid. The time course of the deoxycholic acid specific activity was modeled as a single pool precursor-product system with a variable time delay for the C-7-dehydroxylation of cholic and ursocholic acids (mean delay 0.86 +/- 0.11 days, p less than 0.001 vs. zero delay). Most of this delay probably arises from a slow process of bacterial C-7-dehydroxylation within the colon. These results demonstrate that during ursocholic acid therapy the synthesis of primary bile acids continues whereas the formation of secondary bile acids is greatly increased.