Drugs that alter GI motility are used in:
- Diseases that affect smooth muscle
- Diseases that affect absorption or secretion or motility
- Disease that alter sensitivity of the gut wall
– Speeder uppers of transit time
– Slower downers of transit time
– Antispasmotics (we won’t discuss in this unit)
Prokinetic agents like metoclopramide (Reglan) are also used for GERD
as well as nausea and vomiting related to chemotherapy or anesthesia
They increase motility by acting on smooth muscle innervation and increasing
sensitivity to acetylcholine, they also antagonize dopamine receptors
and therefore may improve nausea.
Are related to dopamine (prolactin inhibiting hormone) antagonism (galactorrhea,
mastalgia, dyskinesias). They may also interfere with absorption of other
drugs because of increased transit time and decreased time for absorption
Erythromycin is closely related to motilin and binds to motilin receptor
sites in GI smooth muscle so can be used as a prokinetic drug but poorly
Cisapride (Propulsid) was taken off the market in 2000 for interaction
with other drugs in P450 enzyme system leading to arrhythmias
Laxatives and Stool Softeners
Before you guys started graduate school, I know you thought that constipation
was really a problem of the elderly. Now you know different and definitely
need to know about laxatives and stool softeners. Laxatives are the
overall category for medications that increase evacuation of the bowel.
Some medications work more on increasing intestinal propulsion and others
more on changing the consistency of the stool by increasing fluid in
Medications Indicated for clean out or disimpaction (every parent’s
Example: Hypertonic phosphate enemas (Fleets)
They work by drawing water into the colon to soften stool and increase
Bulk (Fiber) Agents
Example: Psyllium (Metamucil)
Bulk agents are not absorbed from the GI tract but soften fecal mass
and increases bulk which stretches intestines and increases peristalsis.
WARNING: Requires adequate fluid intake
Side effects: bloating, gas, abdominal pain
Example: Ducosate Sodium (Colace)
Emollients increase absorption of water into colon, and the water mixes
Example: Mineral Oil, which is not absorbed in the GI tract but mixes
with feces and lubricates it.
– Possible impairment of absorption of fat-soluble vitamins over
– May need to add vitamin supplement if > 1 month therapy required
– Cramping, nausea & vomiting
Stimulants are Diphenylmethane derivatives.
Example: Dulcolax (Bisacodyl)
It works by stimulating the enteric NS and increasing Cl- ion secretion
(making the EqM potential more positive) therefore increases smooth
muscle contraction and peristalsis.
Available as suppositories or tablets
• F/E imbalance (loss of Cl-, cramping, nausea, vomiting)
WARNING: High abuse potential
• Anthraquinone derivatives (Senna)
• Castor oil
Try to use stimulant medications only for clean-out,
NOT for maintenance therapy for constipation
Example: Magnesium hydroxide (MOM)
It osmotically draws fluid into the intestine and stimulates cholecystokinin
release which stimulates peristalsis
• F/E imbalance
• Nausea and vomiting
• Neuromuscular s/e from magnesium
• Other: sodium phosphate (fleet’s oral prep)
Example: Lactulose (fructose and galactose)
These cause osmotic water retention in intestines
• GI related
• Hypernatremia and lactic acidosis in high doses
Other examples are Sorbitol
And don’t forget the ever-popular Glycerin suppositories!
Best (as in miracle) drug for constipation
Polyethylene Glycol (Miralax)
If you look at the package insert you will find that Miralax is not
FDA approved for children, but it is given with great anecdotal support by leading gastroenterologists everywhere, including at UNC at Chapel Hill.
It comes as a powder that dissolves in liquid with NO taste or consistency
change to the liquid. This increases compliance tremendously. Try it,
you’ll like it! It is given once or twice daily depending on the
need. Stool softners for constipation and often work best if given for
at least 3-6 months, often much longer.
Side effects, of course, are GI related.
In general, anti-diarrheal drugs should be avoided. Most causes of diarrhea
are viral in children in developed countries and the best therapy is to
keep the child hydrated and well nourished until the illness has passed.
In fact, studies have demonstrated that symptoms will persist longer if
anti-diarrheal drugs are used.
However, there are a few circumstances where you might safely prescribe
or recommend these drugs. True concern for dehydration might be an indication
to temporarily decrease diarrhea water loss. Kids with significant life
events like SATs or possibly another competition that cannot be postponed
or avoided (not necessarily talking about sports here, but possibly, etc.)
Example: Imodium (loperamide)
It is approved for ages 2 and up and works to decrease propulsion by
acting on GI smooth muscle (anticholinergic effects). It may be habit
forming and not because of it’s anti-diarrheal effects!
Most serious is paralytic ileus
Do not use with MAOIs because can lead to hypertensive crisis.
Adsorbents (anti-secretory drugs)
In general are safer than Opioid preparations.
Approved for ages 3 and up and works by increasing adsorption of fluids
from the GI tract.
Bismuth subsalicylate (Pepto-Bismol)
It works the same as above and has an antimicrobial action (sometimes
used for PUD as well).
Allergy to salicylates.
Since is does contain a salicylate (like Aspirin) it is contraindicated
in influenza and chicken pox because of the risk of Reye’s syndrome.
Like anti-diarrheal drugs, anti-emetic drugs are not commonly prescribed
in pediatrics. It is very important to remember that if you need to
treat vomiting you should first assess for:
1) Suspected etiology (treat that if can)
2) If severe, treat for fluid and electrolyte issues (see module 6b)
3) If still unmanageable add drug therapy (see below)
Anti-emetic Drugs Used in Children
The reason you are considering using an anti-emetic is because a child
cannot keep any fluids down, so it makes sense that these 3 products
come as rectal suppositories. There is nothing better than a rectal
medication when a child is vomiting. Trust me!
It works by selectively antagonizing D2 (dopamine) receptors in the
CNS. This medication is also very sedating and can cause respiratory
depression when used in conjunction with other medications that cause
sedation or in overdose.
It is a non-selective antihistamine, antagonizing central and peripheral
H1 receptors. It is only approved for children 2 and older. Side effects
with this medicine are the same as any anti-histamine but with more
central effects causing more sedation.
Tigan has an unknown mechanism of action but it is probably a dopamine
receptor antagonist. This is probably the first choice and has the least
possibility of drug interaction and adverse effects.