The Colonic Transit Time: a Modifiable Determinant of Intestinal Production and Uptake of Microbial Metabolites?

Inclusion Criteria: * Age ≥ 18 and ≤ 85 years * Chronic slow-transit constipation as defined be 4 criteria: 1. having two or fewer spontaneous complete bowel movements week for a minimum of 6 months 2. having one or more of the following symptoms for at least one-quarter of the time: lumpy/hard stools, a sensation of incomplete evacuation, or straining during defecation. 3. slow transit time as determined by Rx colon transit study ("pellet") 4. without evidence of secondary constipation or primary defecation disorder * Need of therapy with prucalopride (i.e., inefficacy of dietary changes and laxatives) * Follow-up visit possible after 4 weeks of treatment * Written informed consent Exclusion Criteria: * History or new diagnosis of organic intestinal disease (e.g., inflammatory bowel disease, malignancy) * Secondary constipation (drug-induced, endocrine, metabolic or neurological disorders, surgery, known or suspected organic disorders of the large intestine, or megacolon) or primary defecation disorder * Use of laxatives two days before start of treatment and during treatment period. If there is no spontaneous bowel movement during 3 consecutive days, rescue treatment with bisacodyl and/or enema is allowed if necessary * Presence of significant co-morbidity (uncontrolled heart, liver and lung disease) * Pregnancy * Chronic kidney disease, i.e., estimated glomerular filtration rate (MDRD) \< 60 ml/min/m² or need of dialysis therapy