Treatment with selective serotonin reuptake inhibitors has been associated with gastrointestinal side effects, including exacerbation of irritable bowel syndrome (1). In contrast, we describe apparent improvement of irritable bowel syndrome correlating with paroxetine treatment and independent of antidepressant response.
Mr. A was 44 years old when he saw his primary care physician for cramping abdominal pain, excessive flatus, frequent diarrhea, and an inability to gain weight (6 feet, 155 lb). These symptoms, present for 30 years, had intensified over 1 year with increased stress. A colonoscopy with a biopsy revealed mild active colitis. Treatment with mesalamine, 800 mg t.i.d., for 9 weeks was not beneficial. Irritable bowel syndrome was diagnosed, and treatment with dicyclomine, 10 mg t.i.d., for 17 weeks was unsuccessful.
At a psychiatric evaluation Mr. A complained of gastrointestinal symptoms, low back pain, and recent stress. He met the criteria for major depressive disorder of moderate severity. Psychotherapy was initiated, and paroxetine, 10 mg/day, was given for 2 weeks, increased to 20 mg/day for 3 weeks, then increased to 30 mg/day. After 2 weeks at 20 mg/day the irritable bowel symptoms fully disappeared, and Mr. A’s depression was partially relieved. His depressive symptoms completely disappeared only after 2 weeks at the 30-mg/day dose.
After 1 year of treatment with paroxetine, 30 mg/day, and with his irritable bowel syndrome and depressive symptoms in remission, Mr. A’s paroxetine therapy was tapered over 3 months. At 5 mg/day he experienced a relapse of postprandial indigestion and loose stools (two to four per day). One week after he discontinued paroxetine, his typical crampy abdominal pain and diarrhea returned, without a relapse of the depression. These symptoms remitted when Mr. A restarted paroxetine, 30 mg/day. He remained asymptomatic for the next 14 months. Then a second slow taper was attempted. At 10 mg/day the irritable bowel symptoms returned, without depression. Maintenance therapy at 20 mg/day has controlled his irritable bowel syndrome symptoms for the past 6 months, and he has reached his highest weight ever, 167 lb.
The patient’s irritable bowel syndrome disappeared with paroxetine treatment and twice returned when the dose was reduced. The slow taper of paroxetine makes it unlikely that the relapses were actually withdrawal symptoms. The mechanism by which paroxetine may improve irritable bowel syndrome is unclear. On the basis of in vitro studies, paroxetine has been found to have anticholinergic effects that might improve bowel symptoms, but clinically, this effect appears minimal (2). For this patient, treatment with an anticholinergic agent, dicyclomine, was ineffective, which raises the possibility that paroxetine may have improved his irritable bowel syndrome by means of a serotonergic mechanism. To our knowledge, there are only two other reports of irritable bowel syndrome improving with serotonergic antidepressant treatment (3, 4).