Treatment of Diarrhea-Predominant Irritable Bowel Syndrome With Paroxetine

Sir: Irritable bowel syndrome (IBS) is a chronic gastrointestinal disorder. The disorder is characterized by chronic abdominal pain and altered bowel habits in the absence of any organic disorder. Treatment of IBS includes dietary modification, psychotherapies, and medications. Among medications, antidepressants may be beneficial in IBS.¹ We report a case in which symptoms of diarrhea-predominant IBS improved with low-dose paroxetine, a widely used antidepressant.

Case report. Mr. A, a 43-year-old man, presented to a gastroenterologist in August 2001 complaining of frequent diarrhea and chronic abdominal pain. These symptoms, present for 3 months, had intensified during the previous month with increased stress. There were no abnormal findings on a physical examination or gastrointestinal endoscopy. He was diagnosed as having IBS. Treatment for 5 months with trimebutine maleate, 300 mg/day, and loperamide, 2 mg/day, was not beneficial. Then, he was referred to our department of psychiatry.

At a psychiatric evaluation, Mr. A reported feeling stress on the job and had mild obsessional thinking that stress must cause diarrhea and eating must exacerbate diarrhea. He did not meet DSM-IV criteria for major depressive disorder or obsessive-compulsive disorder. Supportive psychotherapy was initiated, and paroxetine, 10 mg/day, was added for 1 week and then increased to 20 mg/day. After 3 weeks of treatment at 20 mg/day, his IBS symptoms disappeared and trimebutine maleate and loperamide were discontinued. For the next year, he experienced no IBS symptoms. Paroxetine treatment was then reduced to 10 mg/day and discontinued after 6 months at this dose. Psychotherapy alone has controlled his IBS symptoms for the past year.

This case represents a patient with diarrhea-predominant IBS and mild obsessional thinking. Although treatment with trimebutine maleate and loperamide did not lead to improvement in clinical symptoms, the patient's IBS symptoms disappeared with paroxetine treatment. Paroxetine, a widely used selective serotonin reuptake inhibitor (SSRI), is effective in treating depressive disorders and anxiety disorders, including obsessive-compulsive disorder.

A number of randomized controlled trials have demonstrated decreased symptoms in IBS patients taking low-dose tricyclic antidepressants (TCAs). SSRIs may be useful when IBS is accompanied and exacerbated by a mood disorder, but evidence to support their use is lacking.² The efficacy of SSRIs in patients with IBS has been documented in case reports³ and a pilot open-label study,⁴ but not in controlled studies.⁵

The mechanism of action of SSRIs for IBS is not known but may relate to its effects on the central nervous system and the enteric nervous system.⁵ Low-dose SSRI treatment might be effective for mild obsessional thinking that does not fulfill DSM-IV diagnostic criteria for obsessive-compulsive disorder. Moreover, the anticholinergic effects of paroxetine are milder than those of TCAs, and paroxetine may improve diarrhea and other symptoms of IBS adequately.

Patients with IBS often have obsessional thinking about IBS symptoms. Therefore, SSRIs might have efficacy for IBS even without a diagnosable mental disorder. If IBS symptoms are improved with SSRI treatment in diarrhea-predominant IBS, psychotherapy may be helpful in maintaining improvement. As a result, IBS symptoms may be controlled without medication. This suggests that an SSRI, such as paroxetine, administered in a low dose might be a key drug in early treatment for IBS.