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Irritable Bowel Syndrome (IBS): Pharmacologic Treatments

Irritable Bowel Syndrome (IBS): Pharmacologic TreatmentsAlthough non-pharmacologic therapy is often effective for the treatment of mild irritable bowel syndrome (IBS) symptoms, many patients who experience moderate-to-severe symptoms do not attain adequate relief and are given drug therapy. Pharmacologic therapy is symptom-specific and is intended for use in combination with lifestyle therapy. A review of the literature in 1988 concluded that trials involving IBS therapies were poorly designed and that no treatments had evident efficacy. Although the definition of IBS has been revised and clinical trial criteria have improved since the time of that review, evaluation of irritable bowel syndrome (IBS) medications has been complicated by a high placebo effect (30% to 80%) and lack of a uniform, objective marker for efficacy.

In a recent analysis of 70 randomized, controlled trials performed between 1966 and 1999, only 28 were deemed quality studies (the majority of these studies were limited by methodological flaws, such as vague entry criteria, high drop-out rates, inadequate trial duration, and variable outcome measures) and of those, few established efficacy for the treatments utilized in irritable bowel syndrome (IBS). These criticisms have led to development of clearly defined enrollment criteria and outcome measures in clinical trials for recently approved and investigational medications. Commonly used treatments for IBS, including older agents and two new medications, are discussed in the following sections and are summarized in Table 5. With the exception of alosetron and tegaserod maleate, the therapies discussed have not been reviewed by the FDA for irritable bowel syndrome (IBS).

Table 5:

Common Treatments for irritable bowel syndrome (IBS)
Drug
Usual Adult Dosage Common ADRs*
Antidiarrheals

Cholestyramine

4 g QD to BID Constipation, nausea

Loperamide

2-4 mg up to QID Constipation, drowsiness
Antispasmotic Agents Anticholinergic effects

Dicyclomine

10-20 mg TID to QID

Hyoscyamine regular-release

0.125-0.25 mg TID-QID Xerostomia, tachycardia

Hyoscyamine extended-release

0.375-0.75 mg Q12h
Bulk-Forming Laxatives Bloating, flatulence

Methylcellulose

4-6 g/day in divided doses

Psyllium

2.5-30 g/day in divided doses
Selective Serotonin Reuptake Inhibitors Nausea, diarrhea,
Fluoxetine 10-20 mg QD insomnia, sedation
Paroxetine 10-20 mg QD
Tricyclic Antidepressants Anticholinergic effects
Amitriptyline 10-100 mg QHS
Desipramine 50-150 mg QHS
* Adverse drug reactions

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