Constipation osmotics

Polyethylene glycol (PEG, MiraLax) is an osmotic laxative available only by prescription. It is useful in patients who are experiencing acute constipation and who have had inadequate response to more traditional agents. Principal adverse effects include upset stomach, bloating, cramping, and gas. 

Slow-transit constipation can be treated with chronic administration of osmotic laxatives. Tegaserod maleate 6 mg orally twice daily is an acceptable treatment. Senna, bisacodyl, and other stimulants should be used only when the others fail to deliver the desired effect. 

Lactulose is a disaccharide that causes an osmotic effect retained in the colon. It is generally not recommended as a first-line agent for the treatment of constipation because it is costly and not necessarily more effective than agents such as milk of magnesia. It may be justified as an alternative for acute constipation and has been found to be particularly useful in elderly patients. 

Bisacodyl is a stimulant laxative that does not take long to act and is therefore useful in acute constipation. The bulk-forming laxative ispaghula husk takes longer to act when compared with bisacodyl but is useful for long-term administration. Lactulose, which is an osmotic laxative, has a lag time of about 48 hours before onset of action. Loperamide and kaolin and morphine mixture are antidiarrhoeals used in acute diarrhoea. 

Since food has a buffering effect, antacids are taken between meals (e.g., 1 and 3 h after meals and at bedtime). Nonabsorbable antacids are preferred. Because Mg(OH)2 produces a laxative effect (cause osmotic action, p. 170, release of cholecystokinin by Mg, or both) and Al(OH)3 produces constipation (cause astringent action of AP, p. 178), these two antacids are frequently used in combination. 

Polyethylene Glycol [PEG] 3350 (MiraLax) [Laxative] Uses Occasional constipation Action Osmotic laxative Dose 17 g powder (1 heaping tbsp) in 8 oz (1 cup) of H2O drink max 14 d Caution [C, ] R/0 bowel obst before use Contra GI obst, allergy to PEG Disp Powder for recons bottle cap... 

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). 

A variety of adverse effects have been reported following the use of antacids. If sodium bicarbonate is absorbed, it can cause systemic alkalization and sodium overload. Calcium carbonate may induce hypercalcemia and a rebound increase in gastric secretion secondary to the elevation in circulating calcium levels. Magnesium hydroxide may produce osmotic diarrhea, and the excessive absorption of Mg++ in patients with renal failure may result in central nervous system toxicity. Aluminum hydroxide is associated with constipation serum phosphate levels also may become depressed because of phosphate binding within the gut. The use of antacids in general may interfere with the absorption of a number of antibiotics and other medications. 

High doses of osmotically active agents produce prompt bowel evacuation (purgation) within 1-3 hours. The rapid movement of water into the distal small bowel and colon leads to a high volume of liquid stool followed by rapid relief of constipation. The most commonly used purgatives are magnesium citrate and sodium phosphate. 

Magnesium Osmotic agents increase Usually causes evacuation Simple constipation bowel prep for Magnesium may be absorbed and cause toxicity... 

Lactulose (Constulose, Generlac, Enulose, Others) [Laxative/ Osmotic] Uses Hepatic encephalopathy constipation Action Acidifies the colon, allows ammonia to diffuse into colon Dose Acute hepatic encephalopathy. 30-45 mLPO qlh until soft stools, then tid-qid Chronic laxative therapy 30-45 mL... 

Antacid preparations based on aluminium hydroxide sometimes contain magnesium salts (and carbonate or oxide) to offset the constipating effect of the alumina. This laxative effect of salts such as magnesium sulphate (or citrate) and other saline cathartics such as potassium sodium tartrate is due to their incomplete absorption from the digestive tract so that, by osmotic forces, they retain water in the intestinal lumen. 

These agents may be used for the treatment of acute constipation or the prevention of chronic constipation. Magnesium oxide (milk of magnesia) is a commonly used osmotic laxative. It should not be used for prolonged periods in patients with renal insufficiency due to risk of hypermagnesemia. Sorbitol and lactulose are nonabsorbable sugars that can be used to prevent or... 

Amidotrizoate enemas are still sometimes used to treat meconium ileus or constipation, and it is important to give intravenous fluids so as to avoid dehydration. Hypomagnesemia can also occur (150). Osmotic effects lower in the gastrointestinal tract have even led to distention and cecal perforation (151). Stasis of amidotrizoate in dilated loops of bowel can cause inflammatory changes or necrosis (152,153). 

C Calcium and iron supplementation are common causes of constipation. Polycarbophil, a bulk-forming laxative, exerts its therapeutic effect by increasing the mass and water content of stool and by speeding transit time in the colon. Cascara sagrada and sennosides are cathartics, which speed colonic transit time and alter water and electrolyte transport across the colonic mucosa. Sodium biphosphonate is a saline cathartic, which increases intestinal peristalsis by osmotic properties. Docusate sodium is a stool... 

Antacids neutralize gastric acid, inactivate pepsin, and bind bile salts. Aluminum-containing antacids also suppress HP and enhance mucosal defense. ° G1 adverse effects are most common with antacids and are dose dependent. Magnesium salts cause an osmotic diarrhea, whereas aluminum salts cause constipation. Diarrhea usually predominates with magnesium/aluminum preparations. Aluminum-containing antacids (except aluminum phosphate) form insoluble salts with dietary phosphorus and interfere with phosphorus absorption. Hypophosphatemia occurs most often in patients with low dietary phosphate intake (e.g., malnutrition or alcoholism). Combined treatment with sucralfate may amplify the hypophosphatemia and the potential for aluminum toxicity (see section on sucralfate). 

Glycerin is usually administered as a 3-g suppository and exerts its effect by osmotic action in the rectum. As with most agents given as suppositories, the onset of action is usually less than 30 minutes. Glycerin is considered a very safe laxative, although it may occasionally cause rectal irritation. Its use is acceptable on an intermittent basis for constipation, particularly in children. 

Lactulose is a hyperosmotic agent, which produces increased osmotic pressure within colon and acidifies its contents, resulting in increased stool water content and stool softening. It causes migration of ammonia from blood into colon, where it is converted to ammonium ion and expelled through laxative action. It is indicated in the treatment of constipation and prevention and treatment of portal-systemic encephalopathy, including stages of hepatic precoma and coma. 

This and other nonabsorbable sugars such as sorbitol and mannitol are hydrolyzed in the colon to short-chain fatty acids, which stimulate colonic propulsive motility by osmotically drawing water into the lumen. Sorbitol and lactulose are equally efficacious in the treatment of constipation caused by opioids and vincristine, of constipation in the elderly, and of idiopathic chronic constipation. They are available as 70% solutions, which are given in doses of 15 to 30 mL at night, with increases as needed up to 60 mL per day in divided doses. Effects may not be seen for 24 to 48 hours rafter dosing is begun. Abdominal discomfort or distention and flatulence are relatively common in the first few days of treatment but usually subside with continued administration. A few patients dislike the sweet taste of the preparations dilution with water or administering the preparation with fruit juice can mask the taste. 

Polyethylene glycol is a bowel evacnant that acts as an osmotic agent by cansing water to be retained with the stool. It is nsed in the treatment of occasional constipation use should be limited to 14 days or less. 

In the absence of glucose, infusion of saline via a nasogastric tube at high flow rates induces an osmotic diarrhea which is therapeutically useful in conditions such as cystic fibrosis and severe constipation. Physiological controls on whole-body sodium are mediated through the kidney, but each cell membrane contains the means to regulate intracellular sodium. Hypothalamic mecha-... 

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