Laxatives and Antidiarrheal Drug Therapy
Overview of Laxatives
The irregular, sporadic, and strenuous passage of stool through the
lower gastrointestinal (GI) tract is defined as constipation.
Laxatives are commonly used in the treatment of constipation.
There are five types of laxatives, as shown in the table.
Each laxative class has a differing mechanism of action; however, they
all assist in production of bowel movements (BMs).
The main actions of laxatives are either aiding in fecal progression
through the colon, changing fecal firmness, or promoting the
elimination process through the rectum.
Class Mechanism of Action Examples: Generic
Osmotics (Saline) Draw water into the Polyethylene glycol
intestine, which (PEG) or PEG with
relieves occasional electrolytes
constipation Lactulose
Glycerin
Stimulants (Contact or Stimulate intestinal Bisacodyl
Irritants) walls, which causes the
muscles’ contraction to
clear the bowel
Bulk-Forming Soften and increase Psyllium
bulk of digested food,
so waste can more
easily travel through
and leave the body
Emollients (Stool Increase water in the Docusate sodium
Softeners) stool, which helps Docusate sodium
soften it and makes it with senna
more comfortable to Docusate calcium
pass Mineral oil
Selective Chloride Activate chloride Lubiprostone
Channel Activators channels in the small
intestine, which
enhances fluid
secretion and
movement in the
intestine
Pharmacokinetics of Laxatives
Osmotics (Saline)
o Oral (PO) administration is the preferred method for saline
laxatives.
o Minimal absorption occurs, and excess is eliminated in the stool.
o The nonmetabolized portion is excreted in the urine.
, o Magnesium citrate, an often-used osmotic, binds to albumin and
globulins.
Stimulants (contact or Irritants)
o Bisacodyl, the contact laxative, has minimal absorption from the
GI tract (<5%).
o Its volume of distribution is 289 L.
o The drug is metabolized to bis‐(p‐hydroxyphenyl)‐pyridyl‐2‐
methane (BHPM) in the colon, an active metabolite that is then
converted to a glucuronide salt in the liver.
o Elimination occurs in the feces, but a small portion is excreted in
urine.
Bulk-Forming Laxatives
o Psyllium, a bulk-forming laxative (nonabsorbent and indigestible),
forms a sticky substance when combined with water.
o It is not absorbed, it does not have protein-binding properties,
metabolism is unknown, and it is eliminated in the feces
Emollients (stool softeners)
o A small amount is absorbed from the GI tract with docusate.
o Docusate’s action occurs in the small and large intestines and
produces a BM with the first dose in 1 to 2 days but can also take
up to 3 to 5 days.
o Mineral oil is also an emollient whose onset of action is within 6 to
8 hours if taken orally, or 2 to 15 minutes if administered rectally.
o It is minimally absorbed and distributed into the intestinal mucosa,
liver, spleen, and mesenteric lymph nodes after being excreted via
the feces.
o Metabolism is unknown.
Selective Chloride Channel Activators
o Lubiprostone has low systemic availability after PO administration
and is metabolized fast in the jejunum and stomach by carbonyl
reductase.
o Protein binding is 94%, and there is small dispersion beyond the
tissue of the GI tract.
o It is excreted in urine (60%) and feces (30%).
Pharmacodynamics of Osmotics (Saline)
Glycerin, lactulose, saline products, and salts are considered osmotics,
which are hyperosmolar laxatives.
Sodium or magnesium are in saline products, which are systemically
absorbed in small amounts.
To avoid electrolyte imbalances, it is important to monitor electrolytes
in the blood.
Fecal movement is enhanced when hyperosmolar salts bring water into
the colon, which increases the water content and promotes movement
through the colon.
Overview of Laxatives
The irregular, sporadic, and strenuous passage of stool through the
lower gastrointestinal (GI) tract is defined as constipation.
Laxatives are commonly used in the treatment of constipation.
There are five types of laxatives, as shown in the table.
Each laxative class has a differing mechanism of action; however, they
all assist in production of bowel movements (BMs).
The main actions of laxatives are either aiding in fecal progression
through the colon, changing fecal firmness, or promoting the
elimination process through the rectum.
Class Mechanism of Action Examples: Generic
Osmotics (Saline) Draw water into the Polyethylene glycol
intestine, which (PEG) or PEG with
relieves occasional electrolytes
constipation Lactulose
Glycerin
Stimulants (Contact or Stimulate intestinal Bisacodyl
Irritants) walls, which causes the
muscles’ contraction to
clear the bowel
Bulk-Forming Soften and increase Psyllium
bulk of digested food,
so waste can more
easily travel through
and leave the body
Emollients (Stool Increase water in the Docusate sodium
Softeners) stool, which helps Docusate sodium
soften it and makes it with senna
more comfortable to Docusate calcium
pass Mineral oil
Selective Chloride Activate chloride Lubiprostone
Channel Activators channels in the small
intestine, which
enhances fluid
secretion and
movement in the
intestine
Pharmacokinetics of Laxatives
Osmotics (Saline)
o Oral (PO) administration is the preferred method for saline
laxatives.
o Minimal absorption occurs, and excess is eliminated in the stool.
o The nonmetabolized portion is excreted in the urine.
, o Magnesium citrate, an often-used osmotic, binds to albumin and
globulins.
Stimulants (contact or Irritants)
o Bisacodyl, the contact laxative, has minimal absorption from the
GI tract (<5%).
o Its volume of distribution is 289 L.
o The drug is metabolized to bis‐(p‐hydroxyphenyl)‐pyridyl‐2‐
methane (BHPM) in the colon, an active metabolite that is then
converted to a glucuronide salt in the liver.
o Elimination occurs in the feces, but a small portion is excreted in
urine.
Bulk-Forming Laxatives
o Psyllium, a bulk-forming laxative (nonabsorbent and indigestible),
forms a sticky substance when combined with water.
o It is not absorbed, it does not have protein-binding properties,
metabolism is unknown, and it is eliminated in the feces
Emollients (stool softeners)
o A small amount is absorbed from the GI tract with docusate.
o Docusate’s action occurs in the small and large intestines and
produces a BM with the first dose in 1 to 2 days but can also take
up to 3 to 5 days.
o Mineral oil is also an emollient whose onset of action is within 6 to
8 hours if taken orally, or 2 to 15 minutes if administered rectally.
o It is minimally absorbed and distributed into the intestinal mucosa,
liver, spleen, and mesenteric lymph nodes after being excreted via
the feces.
o Metabolism is unknown.
Selective Chloride Channel Activators
o Lubiprostone has low systemic availability after PO administration
and is metabolized fast in the jejunum and stomach by carbonyl
reductase.
o Protein binding is 94%, and there is small dispersion beyond the
tissue of the GI tract.
o It is excreted in urine (60%) and feces (30%).
Pharmacodynamics of Osmotics (Saline)
Glycerin, lactulose, saline products, and salts are considered osmotics,
which are hyperosmolar laxatives.
Sodium or magnesium are in saline products, which are systemically
absorbed in small amounts.
To avoid electrolyte imbalances, it is important to monitor electrolytes
in the blood.
Fecal movement is enhanced when hyperosmolar salts bring water into
the colon, which increases the water content and promotes movement
through the colon.
