McKenna's Pharmacology for Nursing, 2e

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C H A P T E R 5 8 Drugs affecting gastrointestinal motility

use. Sweating, palpitations, flushing and even fainting have been reported after laxative use. These effects may be related to a sympathetic stress reaction to intense neurostimulation of the GI tract or to the loss of fluid and electrolyte imbalance. A very common adverse effect that is seen with frequent laxative use or laxative abuse is cathartic dependence . This reaction occurs when people use laxa- tives over a long period of time and the GI tract becomes dependent on the vigorous stimulation of the laxative. Without this stimulation, the GI tract does not move for a period of time (i.e. several days), which could lead to constipation and drying of the stool, and ultimately to impaction. Specifically related to chemical stimulants, cascara, although a reliable agent, may have a slow, steady effect or may cause severe cramping and rapid evacuation of the contents of the large intestine. Clinically important drug–drug interactions Because laxatives increase the motility of the GI tract and some interfere with the timing or process of absorp- tion, it is advisable not to take laxatives at the same time as other prescribed medications. The administration of laxatives and other medications should be separated by Bulk stimulants (also called mechanical stimulants) are rapid-acting, aggressive laxatives that cause the faecal matter to increase in bulk. They increase the motility of the GI tract by increasing the fluid in the intesti- nal contents, which enlarges bulk, stimulates local stretch receptors and activates local activity. Avail- able bulk stimulants include the following agents: lactulose ( Actilax ), psyllium ( Metamucil ) and sodium chloride-sodium bicarbonate-potassium chloride solu­ tion ( ColonLYTELY ). Therapeutic actions and indications Bulk stimulants increase the motility of the GI tract by increasing the fluid in the intestinal contents, which enlarges bulk, stimulates local stretch receptors and activates local activity. Lactulose is a saltless osmotic laxative that pulls fluid out of the venous system and into the lumen of the small intestine. Sodium chloride-sodium bicarbonate-potassium chloride ( ColonLYTELY ) contains many electrolytes that pull fluid out of the intestinal wall to increase the bulk of the intestinal contents. Psyllium is a natural substance that forms a gelatine-like bulk out of the intestinal contents. It is milder and less irritating than many other bulk at least 30 minutes. B ulk stimulants

stimulants. People must use caution and drink plenty of water when taking it. See Table 58.1 for usual indications for each of these agents. Pharmacokinetics These drugs are all taken orally. They are directly effective within the gastrointestinal tract and are not generally absorbed systemically. They are rapid acting, causing effects as they pass through the GI tract. Contraindications and cautions Bulk laxatives are contraindicated with allergy to any component of the drug to prevent hypersensitivity reactions ; and in acute abdominal disorders, including appendicitis, diverticulitis and ulcerative colitis, when increased motility could lead to rupture or further exacerbation of the inflammation. Laxatives should be used with caution in heart block, CAD and debilitation, which could be affected by the decrease in absorp- tion and changes in electrolyte levels that can occur ; with great caution during pregnancy and breastfeed- ing because in some cases, stimulation of the GI tract can precipitate labour, and many of these agents cross the placenta and are excreted in breast milk. Sodium chloride-sodium bicarbonate-potassium chloride should be used with caution in any person with a history of seizures because of the risk of electrolyte absorption causing neuronal instability and precipitating seizures. Adverse effects The adverse effects most commonly associated with bulk laxatives are GI effects such as diarrhoea, abdominal cramping and nausea. CNS effects, including dizziness, headache and weakness, are not uncommon and may relate to loss of fluid and electrolyte imbalances that may accompany laxative use. Sweating, palpitations, flushing and even fainting have been reported after laxative use. These effects may be related to a sympa- thetic stress reaction to intense neurostimulation of the GI tract or to the loss of fluid and electrolyte imbalance. People must use caution and take bulk laxatives with plenty of water. If only a little water is used, the laxative may absorb enough fluid in the oesophagus to swell into a gelatine-like mass that can obstruct the oesophagus and cause severe problems. Clinically important drug–drug interactions Bulk laxatives increase the motility of the GI tract, and some interfere with the timing or process of absorp- tion. It is advisable not to take laxatives with other prescribed medications. The administration of laxa- tives and other medications should be separated by at least 30 minutes.