CLINICAL PHARMACOLOGY 2003 (PART 33)

Problems of constipation, diarrhoea and irritable bowel syndrome are common. Infective diarrhoeal diseases are a significant cause of morbidity and mortality worldwide, especially in infants and children.The management of these conditions is reviewed. • Constipation: mode of action and use of drugs • Diarrhoea (drug treatment importance of fluid and electrolyte replacement) • Inflammatory bowel disease • Irritable bowel syndromeSTOOL BULKING AGENTS Dietary fibre comprises the cell walls and supporting structures of vegetables and fruits. Most of the fibre in our diet is in the form of nonstarch polysaccharides (NSP),1 which are not digestible by human enzymes. Fibre...
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CLINICAL PHARMACOLOGY 2003 (PART 33) 32 Intestines SYNOPSIS STOOL BULKING AGENTS Problems of constipation, diarrhoea and Dietary fibre comprises the cell walls and supporting irritable bowel syndrome are common. structures of vegetables and fruits. Most of the fibre Infective diarrhoeal diseases are a significant in our diet is in the form of nonstarch poly- cause of morbidity and mortality worldwide, saccharides (NSP),1 which are not digestible by especially in infants and children.The human enzymes. Fibre may be soluble (pectins, guar, management of these conditions is reviewed. ispaghula) or insoluble (cellulose, hemicelluloses, • Constipation: mode of action and use of lignin). Insoluble fibre has less effect than soluble drugs fibre on the viscosity of gut contents but is a • Diarrhoea (drug treatment importance of stronger laxative because it resists digestion in the fluid and electrolyte replacement) small bowel and so enters the colon intact. In • Inflammatory bowel disease addition it has a vast capacity for retaining water; • Irritable bowel syndrome thus one gram of carrot fibre can hold 23 grams of water.2 It has been proposed that as humans have refined the carbohydrates in their diet over the centuries, so they have deprived themselves of fibre, the ensuing under-filling of the colon being an important cause of constipation, haemorrhoids andConstipation diverticular disease. Stool bulking agents, which add fibre to the diet, are the treatment of choice forThe terms purgative, cathartic, laxative, aperient simple constipation. They act by increasing theand evacuant are synonymous. They are medicines volume and lowering the viscosity of intestinalthat promote defaecation largely by reducing the contents to produce a soft bulky stool, whichviscosity of the contents of the lower colon and are encourages normal reflex bowel activity. The modeclassified as follows: of action of stool bulking agents is thus more• Stool bulking agents physiological than other types of laxative. They• Osmotic laxatives• Faecal softeners 1 The term unavailable complex carbohydrate (UCC) is also• Stimulant laxatives. used and refers to NSP plus undigested (resistant) starch. 2 McConnell A A et al 1974 J Sci Food Agric 25:1427. 639 32 INTESTINESshould be taken with liberal quantities of fluid (at the treatment of hepatic encephalopathy (seeleast 2 litres daily). Chapter 33). Osmotic laxatives are frequently used to clearIndividual preparations the colon for diagnostic procedures or surgery.Bran is the residue left when flour is made from Enemas containing phosphate or citrate effectivelycereals; it contains between 25% and 50% of fibre. evacuate the distal colon and can be useful forThe fibre content of a normal diet can be increased treating obstinate constipation in elderly orby eating wholemeal bread and bran cereals but debilitated patients. Oral preparations containingover-zealous supplementation may cause trouble- magnesium sulphate and citric acid (Citramag) orsome wind (from bacterial fermentation in the colon). polyethylene glycol (Klean Prep) are used in Viscous (soluble) fibres, e.g. ispaghula, are effec- preparation for colonoscopy; they are made uptive and more palatable than bran. Ispaghula husk with water to create an isotonic solution and somecontains mucilage and hemicelluloses which swell patients find the large volumes difficult to tolerate.rapidly in water. Methylcellulose takes up water to Isotonic mannitol was used for the same purpose inswell to a colloid about 25 times its original volume the early ...