Focusing the medical management of constipation exclusively on fibre and bulking agents
In clinical practice, many patients report that they are constipated and feel bloated and distended, despite consuming a significant quantity of dietary fibre. Dietary fibres include several complex, poorly digestible carbohydrates that reach the colon unchanged and are partly fermented by the microbiota. This produces short-chain fatty acids, water, and gas (hydrogen, methane, carbon dioxide). They are usually classified as soluble and insoluble fibres according to their behaviour in aqueous solutions.4,6,15
Several studies have shown that soluble fibre improves functional constipation, and the recommended amount of fibre is about 25-30 g per day. However, while this measure may improve the defecatory frequency and stool consistency, it may worsen symptoms such as abdominal pain, bloating, and distension, especially in patients with constipation-predominant irritable bowel syndrome and in patients complaining of bloating and abdominal distension. Therefore, reducing fibre intake could improve constipation and its associated symptoms.
Bulking agents, either soluble or insoluble fibre, are often recommended as first‐line treatment options for patients with chronic constipation. These agents bind water and prevent its absorption from the lumen by increasing colonic volumes and stool frequency. However, like dietary fibres, bulking agents may also produce side effects such as bloating, distension and flatulence. Hence, treatment with other first-line agents like osmotic laxatives containing polyethylene glycol should be considered in these patients.2,6,15
In patients with poor response to general measures, bulking agents and osmotic laxatives, the next step is to add or change treatment to a stimulant (e.g. bisacodyl, sodium picosulfate, sennosides), secretagogue (e.g. the guanylate cyclase C receptor agonist linaclotide and the chloride channel activator lubiprostone) or prokinetic laxative (e.g. serotonin (5‐HT)‐4 agonist prucalopride, acetylcholinesterase inhibitors)2,4,6,10,15.The mechanisms of action of these pharmacological agents are different but with similar efficacy on constipation. Secretagogues and prokinetics have a high level of evidence and strong recommendation in constipation guidelines. However, their use is limited because they are expensive and are not reimbursed by the health care system in most countries. Stimulant laxatives are cheaper and can be obtained over the counter in most countries, but they have frequent side effects like abdominal cramps and diarrhoea that limit their use. Overuse of stimulant laxatives is associated with a progressive loss of efficacy leading to a continuous increment in the effective dose and dependency of the laxatives to pass stool. Therefore, the European guidelines recommend that the first choice among these second-line pharmacological agents will depend on the patient's characteristics, like the coexistence of abdominal pain or distension, cost/efficacy evaluation, and local preferences.
In patients with opioid‐induced chronic constipation, the treatment of choice is with PAMORA (Peripherally Acting µ‐Opioid Receptor Antagonists: naloxegol, methylnaltrexone, alvimopan, naldemedine) that inhibit the peripheral effects of µ‐opioid analgesics on bowel functions such as reduced GI motility and secretion, and increased fluid absorption. PAMORA do not pass the blood‐brain barrier, ameliorating gastrointestinal function without affecting the central analgesic effects of opioids.2 Also, this group of laxatives exerts prokinetic properties even in the absence of opioid therapy and may be effective in non-opioid-related constipation. In case of constipation due to functional defecation disorders, biofeedback training is the treatment of choice regardless of the presence of abnormal bowel transit time.
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