Cisapride and erythromycin prokinetic effects in gastroparesis due to type 1 (insulin-dependent) diabetes mellitus

Structural basis for motilin and erythromycin recognition by motilin receptor

Motilin is an endogenous peptide hormone almost exclusively expressed in the human gastrointestinal (GI) tract. It activates the motilin receptor (MTLR), a class A G protein-coupled receptor (GPCR), and stimulates GI motility. To our knowledge, MTLR is the first GPCR reported to be activated by macrolide antibiotics, such as erythromycin. It has attracted extensive attention as a potential drug target for GI disorders. We report two structures of G_q-coupled human MTLR bound to motilin and erythromycin. Our structures reveal the recognition mechanism of both ligands and explain the specificity of motilin and ghrelin, a related gut peptide hormone, for their respective receptors. These structures also provide the basis for understanding the different recognition modes of erythromycin by MTLR and ribosome. These findings provide a framework for understanding the physiological regulation of MTLR and guiding drug design targeting MTLR for the treatment of GI motility disorders.

Gastrointestinal dysmotility in critically ill patients

Gastrointestinal (GI) motility disorders are commonly present in critical illness. Up to 60% of critically ill patients have been reported to experience GI dysmotility of some form necessitating therapeutic intervention. It has been attributed to various factors, related to both the underlying disease and the therapeutic interventions undertaken. The assessment of motility disturbances can be challenging in critically ill patients, as the available tests used to detect abnormal motility have major limitations in the setting of an Intensive Care Unit. Critically ill patients with GI dysmotility require a multifaceted treatment approach that addresses multiple causes and utilizes multiple pharmacological pathways. In this review, we discuss the pathophysiology, assessment and management of GI dysmotility in critically ill patients.

Differential expression of motilin receptor in various parts of gastrointestinal tract in dogs

Objectives. The presence of motilin receptor in the GI tract of different animal species has been verified. However, the quantitation of motilin receptor expression in different regions of the GI tract remains unclear. The aim of this study was to investigate the expression of motilin receptor in the GI tract and semiquantitatively compare the expression difference in different GI regions in dogs. Methods. Antrum, duodenum, jejunum, ileum, proximal colon, middle colon, and distal colon were obtained from various parts of the GI tract of six sacrificed dogs. The distribution of motilin receptor was determined by immunohistochemistry. The expression levels of motilin receptor mRNA in different regions were measured by RT-PCR. Results. Motilin receptor was expressed throughout the GI tract in dogs. Multiple comparisons of the mean motilin receptor mRNA expression among various regions were significant (P < 0.05). Motilin receptor mRNA was extensively expressed in duodenum, followed by ileum, jejunum, proximal colon, antrum, middle colon, and distal colon. Immunohistochemistry revealed that motilin receptor immunoreactivity was observed only in the enteric nervous system. Conclusion. Motilin receptor is expressed differentially along the GI tract in dogs. The significantly high expression of motilin receptor mRNA is found in the duodenum.

Drugs acting at 5-HT4 , D2 , motilin, and ghrelin receptors differ markedly in how they affect neuromuscular functions in human isolated stomach

BACKGROUND

Progress in identifying safer, effective drugs to increase gastric emptying is impeded by failed clinical trials. One potential reason for failure is lack of translation from animal models to the human condition. To make progress, the actions of existing drugs and new therapeutic candidates need to be understood in human isolated stomach.

METHODS

Neuromuscular activities were evoked in human gastric antrum circular muscle by electrical field stimulation (EFS), defined phenotypically using pharmacological tools.

KEY RESULTS

EFS evoked cholinergically mediated contractions, attenuated by simultaneous nitrergic activation. The 5-HT4 receptor agonist/D2 antagonist metoclopramide and the selective 5-HT4 agonist prucalopride, facilitated contractions in the absence (respectively, Emax 95 ± 29% and 42 ± 9%, n = 3-6 each concentration) and presence (139 ± 38%, 55 ± 13%, n = 3-5) of the NO synthase inhibitor L-NAME, without affecting submaximal contractions to carbachol; the 5-HT4 antagonist SB204070 prevented facilitation by metoclopramide 100 μM (respectively, -5 (range -26 to 34) and 167 (12-1327)% in presence and absence; n = 5-6). The selective motilin receptor agonist camicinal provided considerably greater facilitation (478 (12-2080)% at 30 μM, n = 8). Domperidone (0.001-100 μM; n = 3-6) and acylated or des-acylated ghrelin (1-300 nM; n = 2-4) had no consistent activity, even with protease inhibitors.

CONCLUSIONS & INFERENCES

5-HT4 receptor agonists show different efficacies. Motilin receptor activation has greater potential to increase gastric emptying, whereas ghrelin and D2 receptor antagonism have no direct activity. Drugs stimulating human gastric motility directly can act regardless of disease mechanisms, whereas drugs without direct activity but an ability to block nausea/vomiting may be effective only if these symptoms exist.

Erythromycin inhibited glycinergic inputs to gastric vagal motoneurons in brainstem slices of newborn rats

BACKGROUND

Motilin has been known to stimulate the motility of digestive organs peripherally via activation of motilin receptors located at gastrointestinal (GI) cholinergic nerve endings and/or smooth muscle cells. Recent studies have indicated that motilin may also promote GI motility via actions in the central nervous system; however the sites of action and the mechanisms are not clear yet. The present study aimed to test the hypothesis that motilin receptor agonist erythromycin alters the synaptic inputs of preganglionic gastric vagal motoneurons (GVMs) located in the dorsal motor nucleus of the vagus (DMV).

METHODS

Gastric vagal motoneurons were retrogradely labeled by fluorescent tracer from the stomach wall of newborn rats. Fluorescently labeled GVMs in DMV were recorded using whole-cell patch-clamp in brainstem slices and the effects of motilin receptor agonist erythromycin on the synaptic inputs were examined.

KEY RESULTS

Erythromycin (100 nmol L(-1), 1 μmol L(-1), 10 μmol L(-1)) significantly inhibited the frequency of glycinergic spontaneous inhibitory postsynaptic currents (sIPSCs) of GVMs and significantly inhibited the amplitude at the concentration of 10 μmol L(-1). These responses were prevented by GM-109, a selective motilin receptor antagonist. In the pre-existence of tetradotoxin (TTX, 1 μmol L(-1)), erythromycin (10 μmol L(-1)) caused significant decreases of the glycinergic miniature inhibitory postsynaptic currents (mIPSCs), in both the frequency and the amplitude. However, erythromycin (10 μmol L(-1)) didn't cause significant changes of the GABAergic sIPSCs.

CONCLUSIONS & INFERENCES

Erythromycin selectively inhibits the glycinergic inputs of GVMs.

Luteolin reduces high glucose-mediated impairment of endothelium-dependent relaxation in rat aorta by reducing oxidative stress

While luteolin, a flavone rich in many plants, has some cardiovascular activity, it is not clear whether luteolin has beneficial effects on the vascular endothelial impairment in hyperglycemia/high glucose. Here, we reveal the protective effect of luteolin on endothelium-dependent relaxation in isolated rat aortic rings exposed to high glucose. The thoracic aorta of male Sprague-Dawley rats was rapidly dissected out and the effect of luteolin on the tension of aortic rings pretreated with high glucose (44mM) for 4h was measured in an organ bath system. The levels of nitric oxide (NO), hydroxy radical (OH(-)) and reactive oxygen species (ROS), and the activity of superoxide dismutase (SOD) and nitric oxide synthase (NOS) were measured in aortas. The vasorelaxation after treatment with luteolin for 8 weeks in aortic rings from diabetic rats was also determined. We found that exposure to high glucose decreased acetylcholine-induced endothelium-dependent relaxation. However, high mannitol had no effect on vasorelaxation. Luteolin evoked a concentration-dependent relaxation in aortic rings previously contracted by phenylephrine, and the pD(2) value was 5.24+/-0.04. The EC(50) of luteolin markedly attenuated the inhibition of relaxation induced by high glucose, which was significantly weakened by pretreatment with l-NAME (0.1mM), but not by indomethacin (0.01mM). Luteolin significantly inhibited the increase of ROS level and OH(-) formation, and the decrease of NO level, NOS and SOD activity caused by high glucose. The improving effect of luteolin on endothelium-dependent vasorelaxation in diabetic rat aortic rings was reversed by pretreatment with l-NAME or methylene blue. The results indicate that the decrease of endothelium-dependent relaxation in rat aortic rings exposed to high glucose is markedly attenuated by luteolin, which may be mediated by reducing oxidative stress and enhancing activity in the NOS-NO pathway.

Effects of tegaserod and erythromycin in upper gut dysmotility: a comparative study

OBJECTIVES

Tegaserod may enhance upper gut transit, but, its prokinetic effects on antral/small bowel motility and how this compares with erythromycin is unknown. We prospectively assessed and compared the effects of tegaserod and erythromycin on upper gut motility.

METHODS

In an open label, non-crossover study, 22 patients (M/F=4/18; mean age=37 years) with symptoms of upper gut dysmotility underwent 24-hour ambulatory antroduodenojejunal manometry with a six-sensor solid state probe. The effects of 12 mg oral tegaserod were compared with 125 mg intravenous erythromycin by quantifying pressure wave activity and assessing motor patterns.

RESULTS

Motor activity increased (p<0.05) in antrum, duodenum and jejunum with both drugs when compared to baseline period. The motor response with tegaserod was higher (p<0.05) in jejunum and occurred during the second or third hours, whereas with erythromycin, it was higher (p<0.05) in antrum and occurred within 30 minutes. After tegaserod, a 'fed-response' like pattern was seen whereas after erythromycin, large amplitude (>100 mmHg) antral contractions at 3 cycles per minute were seen. Following tegaserod and erythromycin, phase III MMCs occurred in 12 (55%) and 8 (36%) patients respectively (p>0.05).

CONCLUSIONS

Both drugs increase upper gut motility and induce MMC's, but exert a differential response. Tegaserod produces a more sustained prokinetic effect in the duodenum/jejunum, whereas erythromycin predominantly increases antral motor activity.

Hormones of the gut-brain axis as targets for the treatment of upper gastrointestinal disorders

The concept of the gut forming the centre of an integrated gut-brain-energy axis - modulating appetite, metabolism and digestion - opens up new paradigms for drugs that can tackle multiple symptoms in complex upper gastrointestinal disorders. These include eating disorders, nausea and vomiting, gastroesophageal reflux disease, gastroparesis, dyspepsia and irritable bowel syndrome. The hormones that modulate gastric motility represent targets for gastric prokinetic drugs, and peptides that modify eating behaviours may be targeted to develop drugs that reduce nausea, a currently poorly treated condition. The gut-brain axis may therefore provide a range of therapeutic opportunities that deliver a more holistic treatment of upper gastrointestinal disorders.

Motilin, ghrelin and related neuropeptides as targets for the treatment of GI diseases

Motilin and ghrelin are released from the upper gut during fasting, to stimulate gastric motility. Additional actions of ghrelin (e.g. changes in appetite, nausea or endocrine functions) improve the possibility of using ghrelin receptor agonists to treat complex disorders such as functional dyspepsia. However, changes in endocrine functions increase the risk of unacceptable side effects. By comparison, the more restricted prokinetic activity of motilin limits the therapeutic possibilities but improves the risk:benefit ratio. Compounds targeting both receptors are in development. Recently, additional peptides have been identified from preproghrelin (obestatin) and prepromotilin. These exert biological activity but their pathophysiological significance is unknown.

Clinical trial: effect of mitemcinal (a motilin agonist) on gastric emptying in patients with gastroparesis - a randomized, multicentre, placebo-controlled study

BACKGROUND

Mitemcinal is an orally active motilin agonist that could potentially improve gastric emptying.

AIM

To investigate the effect of mitemcinal on gastric emptying in patients with idiopathic and diabetic gastroparesis.

METHODS

In a randomized, double-blind design, 106 patients were randomized into four dosing regimens (22 to placebo and 21 each to mitemcinal 10 mg, 20 mg, 30 mg bid or 20 mg tid) for 28 days. A standardized scintigraphic gastric emptying test was performed at screening and again after completing the 4-week protocol.

RESULTS

All doses of mitemcinal showed prokinetic activity. A significant improvement in meal retention at 240 min was noted even in the lowest dose group with the greatest improvement observed with 30 mg bid group (75% vs. 10% in placebo group). Diabetic patients responded better than the idiopathic subgroup. In diabetic patients, blood glucose at 1 h after a meal showed dose-dependent elevation. Although gastroparetic symptoms improved with both mitemcinal and placebo, the prominent placebo effect was not statistically exceeded by mitemcinal. Baseline scintigraphy results exhibited no clear correlation between the severity of gastroparetic symptoms and the status of gastric emptying.

CONCLUSION

Mitemcinal is capable of accelerating gastric emptying in both diabetic and idiopathic patients with gastroparesis.

Efficacy of mitemcinal, a motilin agonist, on gastrointestinal symptoms in patients with symptoms suggesting diabetic gastropathy: a randomized, multi-center, placebo-controlled trial

BACKGROUND

Mitemcinal, an oral motilin agonist, accelerates gastric emptying.

AIM

To investigate if mitemcinal was superior to placebo in relief of symptoms attributed to gastroparesis.

METHODS

In a randomized, double-blind design, 392 insulin-requiring diabetics with symptoms attributable to gastroparesis were treated for 3 months with placebo, mitemcinal 5 or 10 mg bid. On a weekly basis, patients assessed whether there was adequate relief of their gastroparesis symptoms. Patients were classified as Complete Responders (CR) if there were three consecutive positive monthly responses, which required at least 50% of their weekly responses in a month being positive. An Overall Responder (OR) had at least 75% positive weekly responses for the whole treatment period.

RESULTS

Mitemcinal 10 mg produced a significantly better response rate than placebo with a 10.6% increase in the OR (P < 0.05 vs. placebo). Mitemcinal 10 mg also produced statistically significant increases in the CR and OR in the subgroup identified by baseline body mass index (<35 kg/m(2)) and haemoglobin A(1c) (<10%) (P < 0.01 vs. placebo). Adverse events did not differ from placebo frequency levels.

CONCLUSIONS

Mitemcinal can induce a statistically significant response to treatment in a subset of diabetic gastroparesis where future prokinetic clinical trials should be focused.

Differences between the abilities of tegaserod and motilin receptor agonists to stimulate gastric motility in vitro

BACKGROUND AND PURPOSE

Motilin or 5-HT4 receptor agonists stimulate gastrointestinal motility. Differences in activity are suggested but direct comparisons are few. A method was devised to directly compare the gastric prokinetic activities of motilin, the motilin receptor agonist, erythromycin, and the 5-HT4 receptor agonist, tegaserod.

EXPERIMENTAL APPROACH

Gastric prokinetic-like activity was assessed by measuring the ability to facilitate cholinergically-mediated contractions evoked by electrical field stimulation (EFS) in rabbit isolated stomach. Comparisons were made between potency, maximal activity and duration of responses.

KEY RESULTS

Rabbit motilin (r.motilin) 0.003-0.3 microM, [Nle13]motilin 0.003-0.3 microM, erythromycin 0.3-10 microM and tegaserod 0.1-10 microM caused concentration - dependent potentiation of EFS-evoked contractions. The potency ranking was r.motilin = [Nle13]motilin > tegaserod > erythromycin. The Emax ranking was r.motilin = [Nle13]motilin = erythromycin > tegaserod. Responses to r.motilin and [Nle13]motilin faded rapidly (t1/2 9 and 11 min, respectively) whereas those to erythromycin and tegaserod were maintained longer (t1/2 24 and 28 min). The difference did not appear to be due to peptide degradation. A second application of [Nle13]motilin was excitatory after 60 min contact and fade of the initial response (responses to 0.03 and 0.1 microM [Nle13]motilin were not different from those caused by the first application).

CONCLUSIONS AND IMPLICATIONS

Prokinetic-like activities of the 5-HT4 agonist tegaserod and the motilin receptor agonists were compared by measuring changes in cholinergically-mediated contractions. This novel approach highlighted important differences between classes (greater Emax of motilin, compared with tegaserod) and for the first time, within each class (short t1/2 for motilin, compared with erythromycin).

Molecular characterization and distribution of motilin family receptors in the human gastrointestinal tract

BACKGROUND

Motilin and ghrelin have been recognized as important endogenous regulators of gastrointestinal motor function in mammals, mediated respectively by the motilin receptor and by the closely related ghrelin receptor. The aims of this study were to explore the distribution of motilin and ghrelin receptors along the human gastrointestinal tract and to establish the molecular nature of the human motilin receptor.

METHODS

Post mortem and surgical human tissue specimens with no hemorrhage, necrosis, or tumor were obtained from various parts of the gastrointestinal tract. We analyzed levels of expression of mRNA for motilin and ghrelin receptors and examined their molecular identities. Portions of some specimens were also studied by immunohistochemistry for expression of the motilin and ghrelin receptor.

RESULTS

The long form of the motilin receptor, but not the short form, was expressed in all parts of the gastrointestinal tract, and expressed at higher levels in muscle than in mucosa. Motilin receptor immunoreactivity was present in muscle cells and the myenteric plexus, but not in mucosal or submucosal cells. In contrast, ghrelin receptor mRNA was expressed equally in all parts of the gastrointestinal tract, with similar levels of expression in mucosal and muscle layers.

CONCLUSIONS

Both the motilin and ghrelin receptors are expressed along the human gastrointestinal tract, but they have clearly distinct distributions in regard to both level and layer. The diffuse muscle expression of the motilin receptor, at both the levels of the gene and the protein product, along the entire gastrointestinal tract makes it a useful potential target for motilide drugs for dysmotility.

The differential antibacterial and gastrointestinal effects of erythromycin and its chiral isolates

The use of erythromycin has been limited by the gastrointestinal side effect properties, which include abdominal distress and diarrhea. To evaluate the possibility of reducing the toxicity of erythromycin, studies were undertaken to separate erythromycin into chiral isolates and then to test the activity of these chiral isolates on gastrointestinal contractility and bacteriostatic actions. Gastrointestinal contractility was obtained by the use of isolated strips of a rat colon. Antibacterial activity was used by obtaining the MICs of erythromycin and isolated agents against Enterococcus faecalis ATCC 29212. ANOVA was performed using the SPSS v.10 to determine statistical differences in the MICs and the amplitude and frequency of spike bursts. Results were expressed as mean+/-SE (N=5). The MICs (microg/mL) of erythromycin (racemate), chiral isolate X, and chiral isolate Y were 0.45+/-0.29, 0.53+/-0.24 (n.s.), and 0.2+/-0.07 (P<or=0.001), respectively. Erythromycin (racemate) at 10 mol/L, 10 mol/L, 5x10 mol/L, 10 mol/L, and 10 mol/L concentrations caused the amplitude of spike bursts to increase by 18+/-7% (P=n.s.), 43+/-10% (P<or=0.05), 55+/-12% (P<or=0.001), 121+/-23% (P<or=0.001), and 163+/-16% (P<or=0.001), respectively. The chiral isolate Y increased the amplitude of spike bursts at the same concentrations as tested above: 32+/-11% (P<or=0.05), 48+/-14% (P<or=0.001), 84+/-13% (P<or=0.001), 112+/-18% (P<or=0.001), and 121+/-13% (P<or=0.001), respectively. Chiral isolate X caused much reduced effect on the amplitude of spike bursts: 9+/-6% (P=n.s.), 27+/-12% (P=n.s.), 27+/-12% (P=n.s.), 30+/-11% (P=n.s.), and 30+/-11.2% (P=n.s.), respectively. EC50 for erythromycin (mixture) was 0.4x10 mol/L, and for erythromycin Y, it was 0.8x10 mol/L. The addition of erythromycin at 10 mol/L caused the frequency of spike bursts to increase 11+/-7% at 10 mol/L, 5x10 mol/L, 10 mol/L, and 10 mol/L; the changes were 13+/-10% (P=n.s.), 13+/-10% (P=n.s.), 22+/-13% (P=ns), and 39+/-30% (P<or=0.05), respectively. Chiral isolate Y of erythromycin, changed the frequency of spike bursts by 26+/-21% (P=n.s.); 35+/-20% (P=n.s.), 39+/-30% (P=n.s.), 41+/-37% (P=n.s.), and 44+/-36% (P=n.s.) at the respective concentrations as discussed above. Chiral isolate X altered the frequency of spike bursts at the same concentrations as 40+/-30% (P=n.s.), 45+/-30% (P=n.s.), 62+/-41% (P=n.s.), 62+/-41% (P=n.s.), and 52+/-35% (P=n.s.), respectively. Data indicate that erythromycin (racemate) and chiral isolates X and Y possess similar antibacterial activity. It was also shown that erythromycin and chiral isolate Y increase significantly the amplitude of spike bursts compared with baseline. Isolate X does not increase the amplitude of spike bursts in a dose-dependent manner. The frequency of spike bursts is not significantly changed in the presence of erythromycin or the 2 chiral isolates.

Molecular characterization and distribution of motilin family receptors in the human gastrointestinal tract

BACKGROUND

Motilin and ghrelin have been recognized as important endogenous regulators of gastrointestinal motor function in mammals, mediated respectively by the motilin receptor and by the closely related ghrelin receptor. The aims of this study were to explore the distribution of motilin and ghrelin receptors along the human gastrointestinal tract and to establish the molecular nature of the human motilin receptor.

METHODS

Post mortem and surgical human tissue specimens with no hemorrhage, necrosis, or tumor were obtained from various parts of the gastrointestinal tract. We analyzed levels of expression of mRNA for motilin and ghrelin receptors and examined their molecular identities. Portions of some specimens were also studied by immunohistochemistry for expression of the motilin and ghrelin receptor.

RESULTS

The long form of the motilin receptor, but not the short form, was expressed in all parts of the gastrointestinal tract, and expressed at higher levels in muscle than in mucosa. Motilin receptor immunoreactivity was present in muscle cells and the myenteric plexus, but not in mucosal or submucosal cells. In contrast, ghrelin receptor mRNA was expressed equally in all parts of the gastrointestinal tract, with similar levels of expression in mucosal and muscle layers.

CONCLUSIONS

Both the motilin and ghrelin receptors are expressed along the human gastrointestinal tract, but they have clearly distinct distributions in regard to both level and layer. The diffuse muscle expression of the motilin receptor, at both the levels of the gene and the protein product, along the entire gastrointestinal tract makes it a useful potential target for motilide drugs for dysmotility.

Important Facts About Intestinal Feeding Tube Placement

Enteral feeding is desirable when the gastrointestinal tract is functional because it allows better use of nutrients, is safer, and is more cost-effective than parenteral nutrition. Feeding through a gastric tube, however, is often not feasible in severely ill adults and children because of gastric paresis leading to recurrent episodes of gastroesophageal reflux with the risk of subsequent aspiration. Feeding into the small intestine (duodenum or jejunum) through a nasointestinal tube, therefore, is preferred. Unfortunately, no method of enteral feeding is risk free. This literature review addresses the following 10 topics: (a) the reasons why nasointestinal tube feeding is better tolerated by some patients, (b) candidates for nasointestinal tube feeding, (c) options for selecting nasointestinal tubes, (d) recommended methods for predicting the distance to insert nasointestinal tubes, (e) recommended methods for placing nasointestinal tubes, (f) how promotility medications work and whether they facilitate nasointestinal tube placement, (g) nasointestinal tube placement error rate, (h) methods of determining the internal location of nasointestinal tubes, (i) complications associated with nasointestinal tube use, and (j) other pertinent issues surrounding feeding through nasointestinal tubes. The available research evidence is summarized and recommendations for future work are suggested.

Erythromycin in the short- and long-term control of dyspepsia symptoms in patients with gastroparesis

BACKGROUND

Few prokinetic drugs are available to treat gastroparesis. Data are limited on short-term and long-term efficacy of erythromycin as a prokinetic drug.

GOALS

Assess efficacy of low-dose erythromycin suspension to treat gastroparesis.

STUDY

Patients with dyspepsia and gastroparesis by gastric emptying study were treated with low-bulk diet and low-dose (50-100 mg 3 times a day and at bedtime) oral erythromycin suspension. Data were collected by retrospective chart review and telephone questionnaire for short- and long-term follow-up, respectively.

RESULTS

Of 25 patients, 18 had short-term follow-up, 18 had longterm follow-up, and 14 had both. On short-term follow-up, 15 patients (83%) experienced some or dramatic improvement, while 3 (17%) experienced worsening or no change in symptoms (P = 0.005). Mean duration of long-term use was 11 +/- 7 months. On long-term followup, 12 (67%) patients noticed some or dramatic improvement, while 6 (33%) experienced worsening or no change in symptoms (P = 0.16). Correlation (0.7) between short- and long-term response was significant (P < 0.005). Of the 3 patients with poor short-term response, none did well long term. Of the 11 patients with some or dramatic response in short-term, 7 continued to have some response long term. There was no relation between gastric emptying time and response to erythromycin suspension.

CONCLUSIONS

Treatment of gastroparesis with low-dose erythromycin and low-bulk diet results in a dramatic short-term improvement in the majority of patients. Short-term response predicts long-term response. This response may not be as great, possibly due to tachyphylaxis.

Current concepts in diabetic gastroparesis

Diabetic gastroparesis is a common and debilitating condition affecting millions of patients with diabetes mellitus worldwide. Although gastroparesis in diabetes has been known clinically for more than 50 years, treatment options remain very limited. Until recently, the scientific literature has offered few clues regarding the precise aetiology of gastric dysfunction in diabetes.Up to 50% of patients with diabetes may experience postprandial abdominal pain, nausea, vomiting and bloating secondary to gastric dysfunction. There is no clear association between length of disease and the onset of delayed gastric emptying. Gastroparesis affects both type 1 (insulin dependent) and type 2 (non- insulin dependent) forms of diabetes. Diagnosis requires identifying the proper symptom complex, while excluding other entities (peptic ulcer disease, rheumatological diseases, medication effects). The diagnosis of gastroparesis may be confirmed by demonstrating gastric emptying delay during a 4-hour scintigraphic study. Treatment options are limited and rely on dietary modifications, judicious use of available pharmacological agents, and occasionally surgical or endoscopic placement of gastrostomies or jejunostomies. Gastric pacing offers promise for patients with medically refractory gastroparesis but awaits further investigation. Current pharmacological agents for treating gastroparesis include metoclopramide, erythromycin, cisapride (only available via a company-sponsored programme) and domperidone (not US FDA approved). All of these drugs act as promotility agents that increase the number or the intensity of gastric contractions. These medications are not uniformly effective and all have adverse effects that limit their use. Cisapride has been removed from the open market as a result of over 200 reported cases of cardiac toxicity attributed to its use. Unfortunately, there is a paucity of clinical studies that clearly define the efficacy of these agents in diabetic gastroparesis and there are no studies that compare these drugs to each other. The molecular pathophysiology of diabetic gastroparesis is unknown, limiting the development of rational therapies. New studies, primarily in animals, point to a defect in the enteric nervous system as a major molecular cause of abnormal gastric motility in diabetes. This defect is characterised by a loss of nitric oxide signals from nerves to muscles in the gut resulting in delayed gastric emptying. Novel therapies designed to augment nitric oxide signalling are being studied.

Oral erythromycin and symptomatic relief of gastroparesis: a systematic review

OBJECTIVE

Erythromycin is a motilin agonist that greatly increases the fractional rate of gastric emptying. Although a number of studies document the efficacy of erythromycin in improving gastric emptying, little information exists concerning symptom improvement in patients with gastroparesis. The aim of this study was to review clinical trials of erythromycin to determine the efficacy of this agent in producing symptom relief in patients with gastroparesis.

METHODS

A MEDLINE search from 1966 to 2001 was performed to identify all clinical trials using erythromycin in patients with gastroparesis. The search was further limited to clinical trials using symptom assessment as an endpoint. References from index citations were reviewed to identify additional studies. The search was conducted independently by two authors, and discrepancies were resolved by consensus opinion.

RESULTS

Thirty-five clinical trials were identified, and five met inclusion criteria. One study each involved gastroparesis caused by surgery and systemic sclerosis. Three studies evaluated patients with diabetic or idiopathic gastroparesis. No study used symptoms as a primary endpoint. Improvement was reported in 26 of 60 (43%) patients. Individual symptom scores were available for 23 of 60 subjects in these studies, and symptom improvement was seen in 11 of 23 (48%) patients. One study compared erythromycin and metoclopromide in an open-label, crossover fashion, and found no difference between the two agents. All studies were methodologically weak and highly subject to bias. Four of five studies were open-label trials. Sample sizes in all studies were < or =13 subjects, and treatment duration was < or =4 wk in all studies.

CONCLUSIONS

Although clearly a potent prokinetic, limited data exist concerning efficacy of erythromycin in treating gastroparesis. Small sample sizes, uncontrolled designs, short duration, and inadequate symptom assessment limit available studies. Well-designed trials designed to assess symptom relief in gastroparesis are needed.

Pharmacological modulation of human gastric volumes demonstrated noninvasively using SPECT imaging

Three-dimensional single-photon emission computed tomography (SPECT) imaging allows noninvasive measurement of human postprandial gastric accommodation. The aim of this study was to determine whether 99mTCO4-SPECT demonstrates effects on pre- and postprandial gastric volumes of intravenous (i.v.) erythromycin lactobionate and sublingual isosorbide dinitrate, as predicted from previous literature. Twenty volunteers received no medication (controls), while 12 were randomized to either i.v. erythromycin 2 mg kg-1 over 20 min, or 10 mg sublingual isosorbide. After a 10-min preprandial SPECT measurement, a standard 300-mL, 300-kcal liquid meal was ingested, followed by a 20-min postprandial measurement. Gastric images were reconstructed from transaxial images and total volume was measured using the Analyseeth software system. Fasting gastric volume was greater with isosorbide [223 +/- 14 (SE) mL vs. 174 +/- 9 mL, control; P < 0.05], and postprandial volume was lower with erythromycin [393 +/- 27 mL vs. 582 +/- 17 mL, control; P < 0.05]. The ratio of postprandial over fasting volume and mean difference between pre- and postprandial volumes were significantly lower in both drug groups compared to controls. We conclude that 99mTCO4-SPECT imaging is able to semiquantitatively demonstrate pharmacological modulation of fasting gastric volume and postprandial accommodation in humans.

Erythromycin improves gastric emptying in critically ill patients intolerant of nasogastric feeding

OBJECTIVE

To evaluate the effect of intravenous erythromycin on gastric emptying and the success of enteral feeding in mechanically ventilated, critically ill patients with large volume gastric aspirates.

DESIGN

Prospective, double-blind, randomized, and placebo-controlled trial.

SETTING

General intensive care unit in a university hospital.

PATIENTS

Twenty critically ill, mechanically ventilated patients intolerant of nasogastric feeding (indicated by a residual gastric volume of > or =250 mL during feed administration at > or =40 mL/hr).

INTERVENTIONS

After a gastric aspirate of > or =250 mL, which was discarded, the enteral feeding was continued at the previous rate for 3 hrs. Intravenous erythromycin (200 mg) or placebo was then administered over 20 mins. The residual gastric contents were again aspirated and the volume was recorded 1 hr after the infusion began.

MEASUREMENTS AND MAIN RESULTS

Gastric emptying was calculated as volume of feed infused into the stomach over 4 hrs minus the residual volume aspirated. Mean gastric emptying was 139+/-37 (+/-SEM) mL after erythromycin and -2+/-46 mL after placebo (p = .027). Nasogastric feeding was successful in nine of ten patients treated with erythromycin and five of ten who received placebo 1 hr after infusion (chi-square p = .05).

CONCLUSION

In critically ill patients who have large volumes of gastric aspirates indicating a failure to tolerate nasogastric feeding, a single small dose of intravenous erythromycin allows continuation of feed in the short term.

Prokinetic effects of erythromycin after antimotion sickness drugs

Motion sickness and the antimotion sickness drugs scopolamine (SCP) and promethazine (PMZ) inhibit gastric emptying (GE). This study was conducted to determine if erythromycin would exert its well-known prokinetic effects in normal and motion-sick subjects given antimotion sickness drugs. Fifteen fasted volunteers (11 males, 4 females) participated in the study. In control tests, 8 subjects were given intramuscular (i.m.) saline (SAL, 0.5 ml), SCP (0.1 mg), or PMZ (25 mg). GE of liquid (300 ml) containing 1 mCi of Tc 99m diethylenetriaminepentaacetic acid (DTPA) was measured by sequential gastric scintigraphy 30 minutes after i.m. treatments. In other tests, GE was measured in 8 subjects after each i.m. treatment, followed 10 minutes later by 200 mg of erythromycin ethylsuccinate (ESS) suspension given orally. In a third group of tests, 7 subjects received an i.m. treatment, oral EES 10 minutes later, and were then brought to an advanced level of motion sickness short of vomiting. To induce motion sickness, blindfolded subjects made timed head movements while seated in a rotating chair. GE was measured immediately after rotation. GE half-life, rate constant, area under the curve (AUC), and lag time were calculated using conventional mathematical methods for analyzing exponential rate processes. GE parameters calculated for normal and motion-sick subjects given antimotion sickness drugs and EES were compared with those from subjects given i.m. treatments (control) only. In normal subjects, EES significantly (p < 0.05) increased the GE rate constant for all i.m. treatments and reduced the AUC for SAL, SCP, and PMZ by 49% (p < 0.05), 44% (p < 0.05), and 69% (p < 0.01), respectively. In motion-sick subjects, lag time was significantly (p < 0.05) increased, and the rate constant and AUC values were unchanged from control for all i.m. treatments. The authors conclude that oral EES reverses the gastrostatic actions of the antimotion sickness drugs but does not affect the inhibition of gastric emptying associated with motion sickness. The results suggest that motion sickness and antimotion sickness drugs reduce GE through different mechanisms.

Gastrointestinal motor dysfunction, symptoms, and neuropathy in noninsulin-dependent (type 2) diabetes mellitus

Although relatively frequent. diabetic involvement of digestive tract motility has not been investigated extensively in different organs. The authors studied esophageal, gastric, and gallbladder motor function in 35 type 2 (noninsulin-dependent) diabetic patients to determine the extent of gut involvement. Of these patients, 27 (77%) had peripheral neuropathy, 12 (34%) had both peripheral and autonomic neuropathy, and 22 (63%) had gastrointestinal symptoms. Esophageal manometric abnormalities were recorded in 18 patients, and delayed radionuclide emptying of the esophagus was documented in 16 patients, with a 83% concordance between the two tests. Scintigraphic gastric emptying of solids was delayed in 56% of patients, whereas gallbladder emptying after cholecystokinin stimulation was reduced in 69% of them. In 74% of patients at least one of the viscera under investigation showed abnormal motor function; however, only 36% of patients displayed involvement of the three organs. Gastrointestinal symptoms, duration and therapy of diabetes, previous poor glycemic control, and retinopathy did not correlate with the presence or the extent of motor disorders. Neuropathy was not predictive of gastrointestinal involvement and its extent; however, when motor abnormalities were present in patients with neuropathy, these were usually more severe. Gastrointestinal motor disorders are frequent and widespread in type 2 diabetics, regardless of symptoms. Autonomic neuropathy has a poor predictive value on motor disorders (0.75 for the esophagus, 0.5 for the stomach, 0.8 for the gallbladder), thus suggesting the coexistence of other pathophysiologic mechanisms.

Efficacy of prolonged administration of intravenous erythromycin in an ambulatory setting as treatment of severe gastroparesis: one center's experience

Intravenous erythromycin is a potent gastric prokinetic with demonstrated efficacy in the acute therapy of gastroparesis; long-term oral therapy has been limited by tolerance and modest efficacy. Our aim was to review our experience with prolonged administration of intravenous erythromycin in an ambulatory setting as therapy for severe gastroparesis, refractory to usual dietary and oral prokinetic regimens. We conducted a retrospective analysis of patients with gastroparesis treated with intravenous erythromycin for at least 1 month. Information on demographics; origin of gastroparesis; dosage, duration, and route of administration; clinical outcome in the short- and longer-term; and complications were determined. Eleven patients received a total of 14 courses of intravenous erythromycin for a median of 6.5 months (range, 1 to 19 months) at a median dosage of 300 mg/day (range, 150 to 1,000 mg/day). One patient received no benefit, two had complete responses, and all others reported some benefit. Two had dramatic relapse on cessation of therapy and subsequently improved on its resumption. Parenteral nutrition could be discontinued in one of four patients. There were four episodes of line sepsis; two required catheter removal. A nonocclusive thrombus developed at the site of a central line in one patient. Secondary infections or antibiotic resistance were not encountered. Prolonged administration of intravenous erythromycin in an ambulatory setting is feasible, well tolerated, and effective in patients with severe gastroparesis.

The influence of cisapride and clarithromycin on QT intervals in healthy volunteers

OBJECTIVE

Recently a few cases of long QT syndrome were reported during treatment with cisapride. In most of these cases, risk factors for cardiac arrhythmias or pharmacologic interactions might have been involved, and the role of cisapride remained unclear. Macrolides such as clarithromycin potentially interact with the metabolic elimination of cisapride and have overlapping indication areas. We therefore studied whether combined treatment with clarithromycin and cisapride leads to pharmacokinetic changes and increased QT intervals.

METHODS

The study was an open, randomized, 2-way crossover study with washout periods of 1 week. Twelve healthy volunteers were recruited. Treatments were cisapride (10 mg 4 times a day) for 10 days with concomitant clarithromycin (500 mg twice a day) from days 6 through 10, or clarithromycin (500 mg twice a day) for 10 days combined with cisapride (10 mg 4 times a day) from days 6 through 10. Frequent ECG recordings were performed for 24 hours before drug treatment (baseline). After 5 days of monotherapy and combination therapy, frequent ECG recordings and assessments of plasma drug levels were performed for 24 hours.

RESULTS

Clarithromycin alone was associated with a minimal increase in QTc intervals. Monotherapy with 10 mg cisapride 4 times a day led to a concentration-dependent QTc elevation, amounting to 6 ms during steady state. Combination of cisapride and clarithromycin caused an average QTc increase of 25 ms above pretreatment values and 3-fold increases in cisapride concentrations.

CONCLUSIONS

QTc elevations after cisapride or clarithromycin alone remained within the normal range of diurnal variation. Coadministration of cisapride and clarithromycin produced a substantial QT prolongation. The data support the recently purported interaction between cisapride and clarithromycin and thus the filed contraindication to combine these drugs.

Cisapride-induced torsades de pointes

Two cases of torsades de pointes associated with cisapride are presented, both in association with concomitant drug therapy that inhibits cisapride biotransformation. In one case, plasma cisapride was elevated days after the event, strongly supporting a role for accumulation of the drug in causing the arrhythmia. It is emphasized that these adverse drug reactions are not idiosyncratic, but rather are predictable based on an understanding of the underlying mechanisms.