Novel Pilot Study to Treat Symptoms of IBS With Diarrhea Using Combination Therapy of a Low-FODMAP Diet and a Neuromodulator

We hypothesize that adult patients with IBS-D treated with a combination of a low FODMAP diet and mirtazapine will have a greater improvement in global IBS symptoms including abdominal pain and diarrhea in addition to improved quality of life compared to those treated with a low-FODMAP diet only. Global improvement in IBS symptoms will be evaluated using the validated IBS-SSS questionnaire. We will evaluate changes in quality of life using a validated IBS-QoL questionnaire. We will assess the improvement in abdominal pain using a numerical rating system and assess improvements in diarrhea using the Bristol stool form scale. We will assess responses to bloating using a Mayo bloating questionnaire forms. We will assess improvement in diarrhea using the Bristol stool form scale. Improvement in anxiety and any other descriptive information as provided by patients including patients reporting impression of overall severity of symptoms at the beginning, middle, and end of study. Irritable bowel syndrome (IBS) is a common gastrointestinal (GI) disorder that affects up to 10% of the United States adult population. IBS is characterized by recurrent abdominal pain and altered bowel habits, diagnosed using the Rome IV criteria. Approximately one-third of all IBS patients are classified as having IBS with diarrhea (IBS-D), which has no validated treatment algorithm. The American College of Gastroenterology IBS guideline recommends the low-FODMAP (fermentable oligo-, di-, monosaccharide, and polyol) diet as a safe and modestly effective treatment. An analysis of 7 randomized, controlled trials found that the low-FODMAP diet was associated with an improvement in global IBS symptoms. However, despite following the low-FODMAP diet, many patients have persistent abdominal pain, which can be difficult to treat. The mechanisms underlying chronic abdominal pain in patients with IBS are unknown, although visceral and central hypersensitivity are thought to play a role. No medication is FDA-approved for the treatment of abdominal pain in IBS. Mirtazapine is an atypical antidepressant that acts on several classes of receptors. In a small open-label study mirtazapine improved IBS-D symptoms, including abdominal pain.