18 PEG is commonly used in solutions for colon cleansing as polyethylene glycol electrolyte lavage solutions (PEG-ELS) and sulfate-free electrolyte lavage solution (SF-ELS). Polyethylene glycol (PEG) is a isosmotic laxative that is metabolically inert, which binds to water and keeps water retention inside the lumen. Sodium sulfate is a component of some bowel lavage solutions for colon cleansing prior to diagnostic and surgical procedures, 15, 16 but significant absorption may occur in the jejunum that may cause electrolyte disturbances.
Even patients who are otherwise healthy may develop these complications as a result of excessive use. Magnesium containing laxatives are not recommended in patients with renal insufficiency or cardiac dysfunction because the high risk of developing electrolyte disturbances and volume overload from the absorption of magnesium or phosphorus. Other side effects include hypermagnesemia-induced paralytic ileus and hypermagnesemia in patients with renal failure. 14 The use of magnesium in older adults should be used with caution because the high profile of gastrointestinal side effects and magnesium toxicity. Magnesium sulfate is a more potent laxative that tends to produce a large volume of liquid stool and abdominal distention. Standard doses of 40 to 80 mmol of magnesium ion usually provokes a bowel movement within 6 hours. 13 Magnesium oxide has been considered safe to use on a regular basis in mildly constipated patients. Magnesium, sulfate, and phosphate ions are poorly absorbed by the gut and thereby create a hyperosmolar intraluminal environment. Patients also must be encouraged to drink water and maintain hydration when increasing fiber intake. If the constipation has not improved, then commercially available fiber supplements should be tried. To improve the tolerance and adherence you may start with low doses of fiber and increase their dietary fiber intake gradually over the next weeks until ∼20 to 25 g/d. In some patients, these agents also delay gastric emptying and depress appetite.
Insoluble fiber, such as cereal bran, may cause significant abdominal gas and bloating, creating discomfort. The recommended amount of dietary fiber is 20 to 35 grams per day (g/d) and this can be obtained from whole wheat bread, unrefined cereals, citrus fruits, and vegetables. 5, 6 Dietary fiber appears to be effective in relieving mild to moderate, but not severe constipation. A correlation between increasing the daily fiber intake and fecal weight as well as colonic transit time has been demonstrated. Constipation has been associated with a deficiency of dietary fiber in Western society for decades.
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