Bowel Irritant Purgatives

Diphenolmethane derivatives were developed from phenolphthalein, an accidentally discovered laxative, use of which had been noted to result in rare but severe allergic reactions. Bisacodyl and sodium picosul-fate are converted by gut bacteria into the active colon-irritant principle. Given by the enteral route, bisacodyl is subject to hydrolysis of acetyl residues, absorption, conjugation in liver to glucuronic acid (or also to sulfate), and biliary secretion into the duodenum. Oral administration is followed after 6-8 hours by discharge of soft formed stool. When given by suppository, bisacodyl produces its effect within one hour. 

Indications for colon-irritant purgatives are the prevention of straining at stool following surgery, myocardial infarction, or stroke and provision of relief in painful diseases of the anus, e.g fissure, hemorrhoids. 

Purgatives must not be given in abdominal complaints of unclear origin. 

Liquid paraf n (paraf num subliquidum) is almost nonabsorbable and makes feces softer and passed easier. It interferes with the absorption of fat-soluble vitamins by trapping them. The few absorbed paraf n particles may induce formation of foreign-body granulomas in enteric lymph nodes (paraf nomas). Aspiration into the bronchial tract can result in lipoid pneumonia. Because of these adverse effects, its use is not advisable. 

Antiflatulents (carminatives) serve to alleviate meteorism (excessive accumulation of gas in the gastrointestinal tract). Aboral propulsion of intestinal contents is impeded when these are mixed with gas bubbles. Defoaming agents, such as dimeticone (dime-thylpolysiloxane) and simethicone, in combination with charcoal, are given orally to promote separation of gaseous and semisolid contents. 

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The interval between natural stool evacuations depends on the speed with which this colon segment is refilled. A large-bowel irritant purgative clears out the entire colon. 

In the colon, semifluid material entering from the small bowel is thickened by absorption of water and salts (from about 1000 to 150 mL/d). If, due to the action of an irritant purgative, the colon empties prematurely, an enteral loss of NaCl, KCl and water will be incurred. To forestall depletion of NaCl and water, the body responds with an increased release of aldosterone (p. Ltillmann, Color Atlas of Pharmacology... 

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