STUDY SUMMARY
Ondansetron improves stool consistency, severity of IBS symptoms
In a five-week, double-blind crossover RCT, Garsed et al1 compared ondansetron with placebo for symptom relief in 120 patients who met Rome III criteria for IBS-D. All patients were ages 18 to 75 and had no evidence of inflammatory bowel disease. Exclusion criteria included pregnancy or breastfeeding, unwillingness to stop antidiarrheal medication, prior abdominal surgery other than appendectomy or cholecystectomy, or enrollment in another trial.
Patients were started on ondansetron 4 mg/d with dose titration up to 24 mg/d based on response; no dose adjustments were allowed during the last two weeks of the study. There was a two- to three-week washout between treatment periods.
The primary endpoint was average stool consistency in the last two weeks of treatment, as measured by the Bristol Stool Form (BSF) scale.13 The BSF is a visual scale that depicts stool as hard (type 1) to watery (type 7); types 3 and 4 describe normal stools. The study also looked at urgency and frequency of defecation, bowel transit time, and pain scores.
Treatment with ondansetron resulted in a small but statistically significant improvement in stool consistency. The mean difference in BSF score between ondansetron and placebo was –0.9, indicating slightly more formed stool with use of ondansetron. Scores for IBS severity—mild (a score of 75 to 175 out of 500), moderate (175 to 300), or severe (> 300)—were reduced by more points with ondansetron than with placebo (83 ± 9.8 vs 37 ± 9.7, respectively). Although this mean difference of 46 points fell just short of the 50-point threshold that is considered clinically significant, many patients exceeded this threshold.
Compared to those who received placebo, patients who took ondansetron also had less frequent defecation and lower urgency scores. Gut transit time was lengthened in the ondansetron group by 10 hours more than in the placebo group.
Pain scores did not change significantly for patients taking ondansetron, although they experienced significantly fewer days of urgency and bloating. Symptoms typically improved in as little as seven days but returned after ondansetron use stopped (typically within two weeks). Sixty-five percent of patients reported adequate relief with ondansetron, compared to 14% with placebo.
Patients whose diarrhea was more severe at baseline didn’t respond as well to ondansetron as did those whose diarrhea was less severe. The only frequent adverse effect was constipation, which occurred in 9% of patients receiving ondansetron and 2% of those on placebo.
WHAT’S NEW
Another option for IBS-D
A prior, smaller study of ondansetron that used a lower dosage (12 mg/d) suggested benefit in IBS-D.14 In that study, ondansetron decreased diarrhea and functional dyspepsia. The study by Garsed et al1 is the first large RCT to show significantly improved stool consistency, less frequent defecation, and less urgency and bloating from using ondansetron to treat IBS-D.
CAVEATS
Ondansetron doesn’t appear to reduce pain
In Garsed et al,1 patients who received ondansetron did not experience relief from pain, which is one of the main complaints of IBS. However, this study did find slight improvement in formed stools, symptom relief that approached—but did not quite reach—clinical significance, fewer days with urgency and bloating, and less frequent defecation.
This study did not evaluate the long-term effects of ondansetron use. However, ondansetron has been used for other indications for more than 25 years and has been reported to have a low risk for adverse effects.15
CHALLENGES TO IMPLEMENTATION
Remember ondansetron is not for IBS patients with constipation
Proper use of this drug among patients with IBS is key. The primary benefits of ondansetron are limited to IBS patients who have diarrhea, and not constipation. Ondansetron should not be prescribed to IBS patients who experience constipation or those with mixed symptoms.
REFERENCES
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12. Chang L, Chey WD, Harris L, et al. Incidence of ischemic colitis and serious complications of constipation among patients using alosetron: systematic review of clinical trials and post-marketing surveillance data. Am J Gastroenterol. 2006;101:1069-1079.
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15. Gill SK, Einarson A. The safety of drugs for the treatment of nausea and vomiting of pregnancy. Expert Opin Drug Saf. 2007;6:685-694.
ACKNOWLEDGEMENT
The PURLs Surveillance System was supported in part by Grant Number UL1RR024999 from the National Center For Research Resources, a Clinical Translational Science Award to the University of Chicago. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Center For Research Resources or the National Institutes of Health.
Copyright © 2014. The Family Physicians Inquiries Network. All rights reserved.
Reprinted with permission from the Family Physicians Inquiries Network and The Journal of Family Practice. 2014;63(10):600-602.