C H A P T E R 5 8
Drugs affecting gastrointestinal motility
919
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
at least 30 minutes.
B
ulk
stimulants
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
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.
