Week 4 notes 5 - Laxatives are traditionally classified...

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Treatment of Constipation Laxatives are traditionally classified into the following categories: bulk-forming agents, emollients, lubricants, stimulants, saline and osmotic agents. Two new categories of drugs, the chloride channel activators and serotonin agonists, have expanded our options for managing chronic constipation. List of Available Bulk-Forming Agents bran cereals (Raisin Bran) (All Bran) psyllium hydrophyllic muciloid (Metamucil) (Modane) methyl cellulose (Citrucel) calcium polycarbophil (Fiber-Con) Pharmacodynamics of the Bulk-Forming Agents These materials are inert, non-digestible, hygroscopic (water-absorbing) materials which, when consumed, will mix with the forming stool in the lumen of the G.I. tract and, by attracting and holding water molecules, will incorporate water into the forming stool. These materials are not themselves digested or absorbed and will remain in the lumen of the intestinal tract keeping the attached water molecules with them. By adding water content to the stool, two objectives are accomplished. First, the additional water in the stool adds volume to the stool, which, by virtue of the increased bulk, will stretch the walls of the colon and activate the colon's intrinsic nervous system (myenteric plexus) which stimulates peristalsis and promotes colonic peristalsis and evacuation. The second is the softening of the stool that comes with the additional water content provided by the bulk-forming agent. Because these agents are unchanged while in the intestinal tract, they are able to "compete" with the natural water-absorbing function of the colon. By retaining the water in the stool, the stool remains softer and more easily "pushed" by peristalsis toward the rectum and eventual evacuation. Pharmacokinetics of the Bulk-Forming Agents The bulk-forming agents are administered orally. They are inert and not digested or absorbed. They are not metabolized and are excreted unchanged in the stool. Advantages of the Bulk-Forming Agents - Administered orally - Once-a-day dosing usually; some patients with severe chronic constipation may require more than once-a-day amounts. - Available over-the-counter - Inexpensive - Very safe agents; minimal adverse effects - Available in multiple formulations; tablets, powders, cereals, cookies (wafers) available for patient selection. 1
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Treatment of Constipation - Useful for both constipation and some cases of diarrhea; by binding free water, they are able to decrease the fluidity of the stool in some instances of diarrhea and decrease the frequency of diarrhea. - Used in the treatment of laxative abuse; capable of safely substituting for the "habit-forming" agents. - Useful in older adults who may be debilitated; they are very gentle on the physiology of the colon. - Useful in treating the infrequent stooling of patients on poor diets - Useful in patients who must avoid straining; following an M.I. or rectal surgery, etc.
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