Irritable Bowel Syndrome Message Boards | Clinical Trial Guidelines for Pharmacological Treatment of IBS

Pharmacological Options

Pharmacological options aim to control irritable bowel syndrome symptoms, bowel alterations and abdominal pain with drugs mainly targeted to the gastrointestinal tract or the central nervous system.

The majority of the available drugs have been tested and are used in the management of individual symptoms, and not to control the whole range of symptoms inherent in the complex irritable bowel syndrome. Loperamide has been shown to be effective in the control of functional diarrhoea, and osmotic and contact laxatives and polyethylene solution in the control of functional constipation. These agents, however, have no effect on, or may even aggravate, other symptoms, such as pain and bloating.[49,50] In addition, their use is indicated only as a symptomatic, on-demand treatment in selected patients, as their effect may be unpredictable or even undesirable in the majority of irritable bowel syndrome patients who present with an alternating bowel pattern.

The smooth muscle relaxants, cimetropium bromide, pinaverium bromide, octilonium bromide, trimebutine and mebeverine, have been shown to be more effective than placebo in three meta-analyses.[41,51,52] On average, the global symptom improvement with myorelaxants exceeded that of placebo by 22%. However, the benefit was due essentially to their effect on abdominal pain and abdominal distension (18% and 14% over placebo, respectively) with no effect on bowel alterations.[52]

Besides being of limited value, the therapeutic benefit of myorelaxants was demonstrated in clinical trials that were hampered by methodological problems. The trials were performed in non-homogeneous groups of patients who presented with different types of functional bowel alterations and were not selected on the basis of standardized irritable bowel syndrome symptom-based criteria.

Psychotropic drugs, mainly low-dosage tricyclic antidepressants, have been used in non-constipated irritable bowel syndrome patients with abdominal pain as the chief complaint. A meta-analysis based on a few uncontrolled trials indicated that they were useful in about one-third of patients.[53] However, their efficacy has not been assessed in randomized, double-blind, placebo-controlled trials.*

*After submission of this article, a randomised, double-blind, placebo-controlled trial has been published showing that the tricyclic antidepressant desipramine may be effective in clinical subgroups of patients with functional bowel disorders (Drossman DA, Toner BB, Whitehead WE, et al. Gastroenterology 2003; 125: 19-31.

http://www.medscape.com/viewarticle/463164_5

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