Multicentre, Randomised, Placebo-Controlled Trial of Mebeverine in Children with Irritable Bowel Syndrome (IBS) or Functional Abdominal Pain – Not Otherwise Specified (FAP-NOS)

All children aged between 12 and 18 years diagnosed with irritable bowel syndrome or functional abdominal pain – not otherwise specified according to the Rome IV criteria will be invited to participate. The Rome IV criteria form the internationally accepted standard for defining functional gastrointestinal disorders like irritable bowel syndrome and functional abdominal pain – not otherwise specified.1 Before inclusion, all patients undergo routine laboratory testing to exclude underlying organic disorders: complete blood cell count, C-reactive protein, celiac screening (anti-transglutaminase antibodies and IgA), fecal screening on Giardia lamblia if patient presents with diarrhea, and on calprotectin in case an Inflammatory Bowel Disease is suspected. The need for further diagnostic testing is left to the discretion of the treating physician. Finally, according to a recently published guideline by the Rome Foundation for the design of pharmacological clinical trials in children, patients are required to have an average daily pain rate of ≥2 on the Wong Baker Faces Pain Scale. This is a validated pain scale to measure pain intensity. In addition, Informed Consent by both parents and by children aged ≥ 12 years is a necessity before children can be included in the study.

• Current treatment by another health care professional for abdominal symptoms • Previous use of mebeverine • Known hypersensitivity to the active substance or to any of the excipients ((magnesium stearate, polyacrylate dispersion , talc, hypromellose, methacrylic acid – ethyl acrylate copolymer (1:1) dispersion , glycerol triacetate, gelatine, titanium dioxide (E171), shellac (E904), propylene glycol, ammonia solution (concentrated), potassium hydroxide, iron oxide black (E172)). • Unintentional weight loss greater than or equal to 5% of their body weight within the last 3 months • Gastrointestinal blood loss • Recurrent or unexplained fevers • Decreased growth velocity • History of previous abdominal surgeries in the past 3 months • Rome IV criteria diagnosis of functional constipation • Children who tested positive for bacterial or parasites infections • Carbohydrate malabsorption, diagnosed either clinically (2 weeks exclusion diet with resolution of symptoms) or with proper testing (breath test). Children with carbohydrate intolerance who continue to have IBS symptoms while on an exclusion diet can still be included • Significant chronic health condition requiring specialty care (e.g., lithiasis, ureteropelvic junction obstruction, sickle cell, cerebral palsy, hepatic, hematopoietic, renal, endocrine, or metabolic diseases) that could potentially impact the child’s ability to participate or confound the results of the study • Known diagnosis of cystic fibrosis • Known diagnosis of porphyria • Known concomitant organic gastrointestinal disease • Current use of drugs which influence gastrointestinal motility, such as erythromycin, azithromycin, butyl scopolamine, domperidone, peppermint oil capsules, and Iberogast. • Insufficient knowledge of the Dutch language • Pregnancy or current lactation. Women with childbearing potential must have a negative urine pregnancy test within 7 days prior to first dose of study treatment