Therapy of irritable bowel syndrome--an overview

Review article: The rationale for antidepressant therapy in functional gastrointestinal disorders

The rationale for antidepressants in the treatment of functional gastrointestinal disorders (FGDs) has been the subject of much interest. However, because of our incomplete understanding of FGDs, this rationale remains unclear. A key point is whether the high degree of psychiatric co-morbidity associated with FGDs (40-90%) represents a shared pathophysiology or the ascertainment bias of tertiary referral patients. Our aims were four-fold: (i) to review the current rationale for antidepressant therapy in FGDs; (ii) to review the studies comparing the characteristics of FGDs with both organic gastrointestinal disease and psychiatric disorders; (iii) to propose a model of FGDs which explains the high psychiatric co-morbidity; (iv) to compare the treatment regimes and effectiveness of antidepressants in FGDs and psychiatric illnesses. The review highlights two important observations. Firstly, the characteristics of FGDs are similar to those of affective disorders and dissimilar to those of organic disease. Secondly, although antidepressants benefit FGD sufferers, their benefits in psychiatric illnesses are greater. We conclude that, in view of the degree of similarity between FGDs and affective disorders, FGDs could be considered as affective disorders in their own right and, if the prescription of antidepressants conformed to their use in affective disorders, FGD morbidity would be reduced.

Treatment of irritable bowel syndrome with herbal preparations: results of a double-blind, randomized, placebo-controlled, multi-centre trial

BACKGROUND

Herbal medications have been used in many countries for the treatment of patients with irritable bowel syndrome. Controlled data supporting the efficacy of these treatments in patients with irritable bowel syndrome are lacking.

AIM

To assess the efficacy and safety of a commercially available herbal preparation (STW 5) (nine plant extracts), the research herbal preparation STW 5-II (six plant extracts) and the bitter candytuft mono-extract in patients with irritable bowel syndrome.

METHODS

Two hundred and eight patients with irritable bowel syndrome were recruited after standardized diagnostic work-up into a double-blind, placebo-controlled, multi-centre trial and were randomly assigned to receive one of four treatments: commercially available herbal preparation STW 5 (n = 51), research herbal preparation STW 5-II (n = 52), bitter candytuft mono-extract (n = 53) or placebo (n = 52). The main outcome variables were the changes in total abdominal pain and irritable bowel syndrome symptom scores.

RESULTS

Two hundred and three patients completed the trial. STW 5 and STW 5-II were significantly better than placebo in reducing the total abdominal pain score (intention-to-treat: STW 5, P = 0.0009; STW 5-II, P = 0.0005) and the irritable bowel syndrome symptom score (intention-to-treat: STW 5, P = 0.001; STW 5-II, P = 0.0003) at 4 weeks. There were no statistically significant differences between the bitter candytuft mono-extract group and the placebo group (P = 0.1473, P = 0.1207).

CONCLUSIONS

The commercially available herbal preparation STW 5 and its research preparation STW 5-II are both effective in alleviating irritable bowel syndrome symptoms.

Regulatory role of 5-HT and muscarinic receptor antagonists on the migrating myoelectric complex in rats

The 5-HT(3) and 5-HT(4) receptor antagonists alosetron and piboserod, and the muscarinic receptor antagonists PNU-171990A (2-(diisopropylamino)ethyl 1-phenylcyclopentanecarboxylate, hydrochloride) and PNU-174708A (2-(diisopropylamino)ethyl 1-phenylcyclohexanecarboxylate) were studied by electromyography, defining the migrating myoelectric complex (MMC) after i.v. administration in conscious rats. Alosetron prolonged the MMC cycle length from 16.6 to maximally 30.4 min at the dose 0.5 mg kg(-1). Piboserod promptly abolished MMC pattern and prolonged cycle length from 16.5 to >60 min at 0.5 mg kg(-1). PNU-171990A and PNU-174708A had no effect on basal cycle length up to a dose of 20 mg kg(-1). In controls, saline did not change the MMC pattern, while L-hyoscyamine at the same dose, 20 mg kg(-1), prolonged cycle length from 17.6 to 29.0 min. None of the drugs affected duration or propagation velocity of phase III of MMC. Blockade of 5-HT(4) receptors seems to exert a powerful inhibitory effect on motility, 5-HT(3) receptor blockade is less efficient and muscarinic receptor blockade has low efficacy.

The treatment of irritable bowel syndrome

The efforts of clinical researchers, lay organizations and pharmaceutical companies have increased the public profile of irritable bowel syndrome and made it a respectable diagnosis. Diagnostic symptom criteria encourage a firm clinical diagnosis, which is the foundation of a logical management strategy. This begins with education. Reassurance that no structural disease threatens should be tempered with the reality that symptoms are likely to recur over many years. Patients expect diet and lifestyle advice, even if this is not specific to irritable bowel syndrome. Only a few of those with irritable bowel syndrome see doctors, and even fewer see specialists. Therefore, the treating physician should ascertain the reason for the visit, the patient's fears and the presence of any comorbid illness, such as depression, that might require treatment in its own right. No drug treatment is useful for all of the symptoms of irritable bowel syndrome, and many patients require no drug at all. If used, drugs should target the predominant symptom. Alosetron, a 5-HT3 antagonist, is effective in treating women with irritable bowel syndrome who also have diarrhoea. Tegaserod, a 5-HT4 agonist, is useful for women with irritable bowel syndrome who are constipated. Most patients with irritable bowel syndrome need psychological support. Reassurance, discussion and relaxation techniques can be provided by the family doctor. Difficult psychopathology may require referral to a mental health professional, and the gastroenterologist can settle diagnostic uncertainties. In all cases, successful treatment depends on a confident diagnosis and the strength of the doctor-patient relationship.

Drug treatment options for irritable bowel syndrome: managing for success

Irritable bowel syndrome (IBS) is a functional gut disorder the diagnosis of which is based on clinical symptoms as set forth by the Rome criteria. As the population ages, especially with the population of patients >75 years of age expanding greatly over the next 10 years, IBS is becoming one of the most common diseases of the elderly. Thus far, developing treatment strategies for patients with IBS has been difficult because of the lack of pharmacological targets and the wide range of symptomatology. Additionally, demonstration of a therapeutic benefit is difficult in the presence of a high placebo response observed regardless of the therapy employed. Fibre, antidiarrhoeals and antispasmodics all play some role in the symptomatic treatment of IBS. With the evolution of IBS as a disorder of visceral hypersensitivity, new drugs have been developed that target the enteric nervous system. Tricyclic antidepressants (TCAs) have been found to target the enteric neurons and play a role in pain modulation. Currently, the TCAs are recommended only for severe cases of IBS pain. The newest class of drugs to be approved for use in IBS are the serotonin (5-hydroxytryptamine; 5-HT) antagonists. Specifically, the 5-HT3 receptor antagonists have been shown to decrease symptoms in female patients with IBS. A related class of drugs, the 5-HT4 receptor agonists, is being developed for the treatment of constipation-predominant IBS. Further investigation into the role of spinal afferent neurons in visceral hypersensitivity is at the forefront of IBS research. Several experimental drug therapies for IBS are also discussed in this review including N-methyl-D-aspartate receptor antagonists, neurokinin-1 receptor antagonists, octreotide, clonidine and the selective M3 receptor antagonist, zamifenacin.