Laxatives, bulk

Distension of the intestinal wall by bowel contents stimulates propulsive movements of the gut musculature (peristalsis). Activation of intramural mechanoreceptors induces a neurally mediated ascending reflex contraction (red in A) and descending relaxation (blue) whereby the intraluminal bolus is moved in the anal direction. 

Osmotically active laxatives (C) are soluble but nonabsorbable particles that retain water in the bowel by virtue of their osmotic action. The osmotic pressure of bowel contents always corresponds to that of the extracellular space because the intestinal mucosa is unable to maintain a higher or lower osmotic pressure of the luminal contents. Therefore, absorption of molecules (e. g., glucose, NaCl) occurs iso-osmotically, i. e solute molecules are followed by a corresponding amount of water. Conversely, water remains in the bowel when molecules cannot be absorbed. 

Luellmann, Color Atlas of Pharmacology All rights reserved. Usage subject to terms 

Osmotic laxative effects are also produced by the polyhydric alcohols mannitol and sorbitol, which unlike glucose cannot be transported through the intestinal mucosa. 

Since the disaccharide lactulose cannot be hydrolyzed by digestive enzymes, it also acts as an osmotic laxative. Fermentation of lactulose by colon bacteria leads to acidification of bowel contents and a reduced number of bacteria. Lactulose is used in liver failure to forestall hepatic coma by preventing bacterial production of ammonia and its subsequent absorption (absorbable NH3 — nonabsorbable NH4 ). Another disaccharide, lac-titol, produces a similar effect. 

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Dietary fibers are used in several food categories, including breakfast cereals, pasta, snack foods, and baked goods, as well as some pharmaceutical categories such as enteral nutritionals, bulk laxatives, and diet beverage mixes (31). The common dietary fiber additives and their sources are given (32). 

The majority of the imported gum karaya is used by the pharmaceutical industry as a bulk laxative, in dental adhesives, and in sealing gaskets for colostomy bags. 

Bisacodyl (Dulcolax, 5-10 mg orally (tabs) or rectally Second-line agent after bulk laxatives... 

Esophageal, gastric, small intestinal, and rectal obstruction caused by the accumulation of mucilaginous components of bulk laxatives have occurred. 

If drugs are used, the first choice should be a bulk laxative, e.g. isphagula or sterculia gum. Nonabsorbent carbohydrates with osmotic activity also work well but often cause flatulence. Salinic laxatives like polyethylene glycol and magnesium oxide are very effective but often cause stomach upsets like flatulence and abdominal pain. Tegaserod, a 5-HT4 partial agonist, appears to improve the frequency of bowel movements in those with chronic constipation (see Evans et ah, 2007). 

Laxatives are used to increase stool frequency and reduce stool viscosity. Even with long-term use, bulk laxatives and pure osmolar laxatives do not predispose patients to formation of a cathartic-type colon and should be the initial agents used for chronic constipation after a structural obstructing lesion has been excluded. Laxatives are also used before radiological, endoscopic, and abdominal surgical procedures such preparations quickly empty the colon of fecal material. Nonabsorbable hyperosmolar solutions or saline laxatives are used for this purpose. Classification and comparison of representative laxatives are provided in Table 40.1. 

Fagerberg. Occupational allergy in nurses to a bulk laxative. Allergy 1979 34(1) 51-55. 

This gum is used as a bulk laxative, as an agent for forming emulsions and suspensions, and as a dental and stoma applicance adhesive. 

Bulk-Forming Laxatives. These agents absorb water and swell within the lower GI tract. The increased size of the water-laden laxative stretches the bowel, thus stimulating intestinal movement (peristalsis). Bulk laxatives commonly contain natural and semisynthetic dietary fiber such as bran, psyllium, and methylcellulose. 

The bulk laxatives include hydrophilic colloids (from indigestible parts of fruits and vegetables). They form gels in the large intestine, causing water retention and intestinal distension, thereby increasing... 

Bulk laxatives are really a more long-term solution. Bisacodyl may be an alternative stimulant laxative, but is likely to have similar adverse effects. 

Medical treatments of IBS are limited. Laxatives (particularly dietary fibre and bulking laxatives such as ispaghula) and antidiarrhoeals (loperamide and sometimes codeine) are prescribed to manage the symptoms of altered bowel habit. Colestyramine is of use in those with diarrhoea caused by bile salt... 

As Mrs P has been referred to a hospital clinic, it is likely that dietary measures have been tried. Therefore a bulking laxative such as ispaghula may be of benefit. As she suffers from cramping an antimuscarinic antispasmodic such as dicycloverine may be of benefit, although some caution is needed, as it may exacerbate her constipation. 

As shown on Table III, the subjects fed 20 g of hemicellulose from purified psyllium fiber excreted significantly more manganese in the feces than when they were fed bread without the hemicellulose supplement. Unlike wheat bran, purified psyllium fiber (sold commercially as a bulk laxative) contains no manganese or phytates hence, any change in fecal manganese excretion when psyllium fiber is added to human diets can probably be credited to the mixture of hemicellulose comprising this product. 

Plantago seeds are widely used as bulk laxatives under the names of psyllium (from P. psyllium or P. indica) and ispaghula (from P. ovata). The possibility that the intestinal absorption of lithium and other drugs may be inhibited should also be considered (658). 

A 69-year-old man with Parkinson s disease developed severe dysphagia after taking granules of the bulk laxative Perdiem (82% psyllium and 18% senna formulated as granules). Disimpaction of the bezoar was performed via a rigid endoscope under general anaesthesia. 

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