C H A P T E R 5 8
Drugs affecting gastrointestinal motility
917
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
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.
BOX 58.1
Drug therapy across the lifespan
Laxatives and antidiarrhoeal agents
CHILDREN
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,
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.
