(Ex-Lax, Feen-A-Mint, Correctol), bisacodyl (Dulcolax), cascara sagrada, senna
(Senokot), and castor oil (purgative). Bisacodyl and phenolphthalein are two of the
most frequently used and abused laxatives because they can be purchased over-
the-counter.
Results occur in 6 to 12 hours. Stimulant laxatives such as bisacodyl are used
to empty the bowel before diagnostic tests (for example, barium enema) because
they are minimally absorbed from the GI tract. Most are excreted in feces.
However, a small amount of bisacodyl absorption excreted in the urine changes
the color to reddish-brown. With excessive use, fluid and electrolyte imbalances
can occur (especially potassium and calcium). Mild cramping and diarrhea are
side effects.
Caster oil is a harsh laxative (purgative) that acts on the small bowel and
produces a watery stool within 2 to 6 hours. Therefore, this shouldn’t be taken
at bedtime. Caster oil is used mainly for bowel preparation and seldom used
to correct constipation. Caster oil should not be used in early pregnancy
because it stimulates uterine contractions and spontaneous abortion can occur.
Prolonged use of Caster oil can damage nerves resulting in loss of intestinal
muscular tone.
Bulk-forming
Bulk-forming laxatives are natural fibrous substances that promote large, soft
stools by absorbing water into the intestines and increasing fecal bulk and peri-
stalsis. Bulk-forming laxatives are non-absorbable. Defecation usually occurs
within 8 to 24 hours but can take up to 3 days after the start of therapy for the
stool to become soft and formed.
Powdered bulk-forming laxatives come in flavored and sugar-free prepara-
tions and should be mixed in a glass of water or juice, stirred. The patient should
drink it immediately, followed by a half to a full glass of water. Insufficient
fluid intake can cause the drug to solidify in the GI tract, resulting in intestinal
obstruction. Bulk-forming laxatives do not cause dependence and may be
used by patients with diverticulosis, irritable bowel syndrome, ileostomy
and colostomy.
Calcium polycarbophil (FiberCon), methylcellulose (Citrucel), fiber granules
(Perdiem), and psyllium hydrophilic mucilloid (Metamucil) are examples of
bulk-forming laxatives. Patients with hypercalcemia should avoid calcium poly-
carbophil because of the calcium in the drug. Metamucil is a nondigestible and
nonabsorbent substance that when mixed with water, becomes a viscous solu-
tion. There is no protein-binding or half-life for the drug. It is excreted in
the feces. There are no systemic effects. Nausea can occur with excessive use.
The dry form can cause abdominal cramps.
CHAPTER 18 Gastrointestinal System^339