Irritable bowel syndrome (IBS) is less a single disease than a syndrome of “complex pathophysiology,” said Brooks D Cash, MD, FACG, in his presentation at the American College of Gastroenterology’s (ACG) session on pharmacotherapy on October 22, 2021.  

Dr Cash is the Dan and Lillie Sterling Professor of Medicine and chief of the division of gastroenterology, hepatology, and nutrition at the University of Texas Health Science Center in Houston, Texas.

He explained that the ACG’s recent guidelines addressed 16 questions on therapeutic options for IBS, from the low FODMAP diet to probotics and more.

Fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAPs) are short-chain carbohydrates often poorly absorbed in the small intestine. The theory behind the low FODMAP diet is to eliminate these carbohydrates for a short period, then reintroduce them slowly to determine which, if any, may be causing abdominal pain, gas, distention, and/or bloating.

ACG gives the low FODMAP diet conditional recommendation due to a very low quality of evidence, Dr Cash explained. “The primary outcome is global improvement in IBS; abdominal pain is an outcome of interest. There is very low quality of evidence that the low FODMAP diet is effective in reducing symptoms.” He also noted that ACG found “insufficient evidence to recommend a gluten-free diet to reduce IBS symptoms.”

In the case of fiber, ACG gave soluble fiber a strong recommendation, with a moderate quality. of evidence for its ability to improve global symptoms of IBS. Bran did not appear to be of benefit but there was no evidence of harm, Dr Cash explained. The addition of soluble fiber to the diet appears to be “a reasonable first-line treatment” especially for IBS with constipation (IBS-C).

While antispasmodics have been used for decades as therapeutics for IBS, Dr Cash noted that guidelines—which only assessed the agents available in the US—give them a conditional recommendation based on a very low quality of evidence. “From the global perspective,” he said, “according to a Cochrane review, several agents that are not available in US have shown benefit.” Peppermint oil, which received a recommendation on a low quality of evidence, did appear to show benefit, primarily in the treatment of abdominal pain.

Probiotics also received a conditional recommendation based on very low quality of evidence. “They were superior to placebo but had only a modest impact on abdominal pain,” he stated.

The guidelines state that some evidence supports using polyethylene glycol (PEG) for chronic constipation but Dr Cash noted that it does not improve abdominal pain. “It’s reasonable as adjunctive therapy.”

Lubiprostone—the oldest IBS-C therapy approved by the FDA—is a type 2 chloride channel activator that received a strong recommendation on moderate quality of evidence for the treatment of IBS-C. The guanylate cyclase-C agonists, including linaclotide and plecanatid received a strong recommendation based on highly quality of evidence for the treatment of IBS-C, Dr Cash stated. Linaclotide has demonstrated “a more than 30% reduction in abdominal pain,” he said.

The prokinetic therapy tegaserod “increases peristalsis and propulsion and can give considerable or complete relief of at least 50%” among patients with IBS-C, Dr Cash explained. Although it was taken off the market in 2007 due to concerns about cardiovascular adverse effects, it has been reintroduced for use in treating IBS-C in woman under the age of 65 without cardiovascular risk factors who have not responded to secretagogues. The ACG has given it a strong recommendation on a low quality of evidence.

Bile acid sequestrants were not recommended for the treatment of IBS-D, while rifaxmin received a strong recommendation for this condition, Dr Cash said. “This antibiotic is soluble in the small bowel and gives relief of global IBS symptoms and bloating.

Alosetron, the oldest approved IBS-D therapy received a conditional recommendation of low quality of evidence, while eluxadoline was given a conditional recommendation with moderate quality of evidence.  

Antidepressants—particularly tricyclics—received a strong recommendation on moderate quality of evidence due to their analgesic and neuromodulatory effects. The newer antidepressants, including selective serotonin reuptake inhibitors and serotonin-norepinephrine reuptake inhibitors have not yet been widely studied in the content of IBS treatment, Dr Cash said.  

Fecal microbiotal transplant received a strong recommendation against use in IBS, Dr Cash stated. “It’s not ready for prime time in IBS but we may see this evolve over the next few years.”

--Rebecca Mashaw

Cash, BD. ACG clinical practice guideline on pharmacotherapy f or IBS. Presented at the American College of Gastroenterology annual meeting, October 22, 2021. Las Vegas, Nevada.