McKenna's Pharmacology for Nursing, 2e

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

D rugs used to affect the motor activity or motility of the gastrointestinal (GI) tract can do so in several dif- ferent ways. They can be used to speed up or improve the movement of intestinal contents along the GI tract when movement becomes too slow or sluggish, to allow for proper absorption of nutrients and excre- tion of wastes, as in constipation . Drugs are also used to increase the tone of the GI tract and to stimulate motility throughout the system. They can also be used to decrease movement along the GI tract when rapid movement decreases the time for the absorption of nutri- ents, leading to a loss of water and nutrients, and the discomfort of diarrhoea . This chapter addresses three major categories of drugs: laxatives, GI stimulants and antidiarrhoeal agents. See Figure 58.1 for sites of action of these drugs on gastrointestinal motility. Box 58.1 highlights important considerations related to laxa- tives and other drugs affecting GI motility, based on the person’s age. Laxatives should not be used in children routinely. Proper diet, including roughage, plenty of fluids and exercise, should be tried first if a child has a tendency to become constipated. Lubricants can be used in older children; harsh stimulants should be avoided. Children with encopresis, however, are often given senna preparations or liquid paraffin to help them to evacuate the massive stool. Children receiving these agents should use them for only a short period and should be evaluated for potential underlying medical or nutritional problems if they are not able to return to normal function. ADULTS Adults who use laxatives need to be cautioned not to become dependent. Proper diet, exercise and adequate intake of fluids should keep the gastrointestinal tract functioning normally. If an antidiarrhoeal is needed, adults should be carefully instructed in the proper dosing of the drug and monitoring of their total use to avoid excessive dose. PREGNANCY AND BREASTFEEDING The safety for the use of these drugs during pregnancy and breastfeeding has not been established. Use should be reserved for those situations in which the benefit to the mother outweighs the potential risk to the fetus. A mild stool softener is often used after delivery.The drugs may enter breast milk and also may affect gastrointestinal activity in the neonate. It is advised that caution be used if one of these drugs is prescribed during breastfeeding. OLDER ADULTS Older adults are more likely to develop adverse effects associated with the use of these drugs, including sedation, BOX 58.1 Laxatives and antidiarrhoeal agents CHILDREN

LAXATIVES Laxative, or cathartic, drugs (Table 58.1) are indicated for the short-term relief of constipation; to prevent straining when it is clinically undesirable (such as after surgery, myocardial infarction or after vaginal birth); to evacuate the bowel for diagnostic procedures; to remove ingested poisons from the lower GI tract; and as an adjunct in anthelmintic therapy when it is desirable to flush helminths (intestinal worms) from the GI tract (see Figure 58.1). Most laxatives are available in over- the-counter (OTC) preparations, and they are often abused by people who then become dependent on them for stimulation of GI movement. Such individuals may develop chronic intestinal disorders as a result. Measures such as instituting proper diet and exercise, and taking advantage of the actions of the intestinal reflexes have eliminated the need for laxatives in many situations; therefore, these agents are used less frequently than they once were in clinical practice. confusion, dizziness, electrolyte disturbances, fluid imbalance and cardiovascular effects. Safety measures may be needed if these effects occur and interfere with the person’s mobility and balance. Older people also may be taking other drugs that are associated with constipation and may need help to prevent severe problems from developing. Older adults are more likely to have renal and/ or hepatic impairment related to underlying medical conditions, which could interfere with the metabolism and excretion of the antidiarrhoeal drugs.The dose for older adults should be started at a lower level than recommended for younger adults.The person should be monitored very closely, and dose adjustment should be made based on response. These people also need to be alerted to the potential for toxic effects when using over-the-counter (OTC) preparations and should be advised to check with their healthcare provider before beginning any OTC drug regimen. A psyllium product is the agent of choice with older adults because there is less risk of adverse reactions.The person needs to be cautioned to drink plenty of fluid after taking one of these agents to prevent problems that can occur if the drug starts to pull in fluid while still in the oesophagus. The older adult should be encouraged to drink plenty of fluids, to exercise every day and to get plenty of roughage in the diet. Many older adults have established routines, such as drinking warm water or prune juice at the same time each morning, that are disrupted with illness or hospitalisation.These people should be encouraged and helped to try to maintain their usual protocol as much as possible.

Drug therapy across the lifespan