Metoclopramide
Metoclopramide is a centrally acting anti-vomiting
(antiemetic) medication that stimulates the motility of the upper GI tract. It
has minimal effect on the lower GI tract and colon. Metoclopramide increases
peristalsis of the small intestine and increases tone and strength of
contractions in the stomach while causing relaxation of the pyloric sphincter.
Consequently, metoclopramide speeds gastric emptying and, possibly, intestinal
transit times. It does not stimulate gastric, pancreatic or biliary secretions.
It is used primarily for slow gastric motility and the treatment of vomiting.
Metoclopramide is used to treat:
- Nausea
- Vomiting
- Reflux Disease
Metoclopramide acts as a central antiemetic by blocking
the uptake of dopamine at the chemo-receptor trigger zone in dogs. Additionally,
part of its actions on the upper GI tract include increasing the sphincter
pressure in the lower esophagus and reducing gastroesophageal reflux, which also
may be helpful for decreasing vomiting.
How Metoclopramide Works
One of the stomach's most important functions is to
grind the food we eat into a fine slurry that passes freely through the
intestines. A strong rhythm of contraction is necessary to affect this and this
rhythm creates the stomach's motility.
Motility disorders are common and may be chronic (of
long duration) or of sudden onset. When motility is reduced in the stomach, food
pools there and creates a sensation of nausea and bloating. In some cases, bile
refluxes from the intestine back into the stomach, causing irritation and more
nausea. Metoclopramide normalizes stomach contractions so that food and bile can
pass in the correct direction.
An additional effect of metoclopramide is helpful in the
control of nausea. There is a biochemical barrier separating the brain and
central nervous system from the blood stream so that only certain biochemicals
can cross over. This partition is called the blood-brain barrier. Metoclopramide
is able to cross the blood-brain barrier and act on the brain directly to
control the sensation of nausea.
Metoclopramide thus helps the vomiting patient by
normalizing stomach motility and acting directly on the brain to reduce the
sensation of nausea.
Signs of nausea in pets include:
- Loss of appetite
- Vomiting
- Drooling
- Loud stomach or intestinal sounds
- Chewing motions
Metoclopramide can be used to control nausea in any
situation except in the event of stomach or intestinal obstruction. If a
motility problem is suspected (a classical history would include vomiting food
many hours after eating), metoclopramide should also be helpful. If a motility
disorder extends beyond the stomach (for example, a colon motility disorder
might lead to constipation), metoclopramide would not expected to be helpful.
Dosage:
Dogs and Cats: 0.2-0.5 mg/kg every 6-8 hours
orally, IV or IM, or 1-2 mg/kg every 2-4 hours by continuous IV infusion, or
approximately 0.1-0.2 mg/kg every hour.
Horses: 0.125-0.25 mg/kg/hr IC [added to IV
fluids].
Metoclopramide is best given 20 minutes before a meal.
Side Effects
Side effects are rare with metoclopramide but generally
stem from the ability to penetrate the blood-brain barrier. Animals predisposed
to seizures (i.e., epileptics) may experience seizures, although this should not
be a problem for normal animals. Use cautiously in horses because of
excitement.
Some animals experience drowsiness and others will
experience marked hyperactivity. Hyperactivity can be reversed with a dose of
Benedryl (diphenhydramine).
Constipation has been reported as a side effect in some
individuals. This is not a common side effect.
If you suspect your pet is having an adverse reaction to metoclopramide,
discontinue the medication and inform your veterinarian. There is another
motility modifier called cisapride (Propulsid) that may be a good alternative.
This medication does not cross the blood-brain barrier and hence does not have
the behavioral side effects that metoclopramide can, but it also does not reduce
the sensation of nausea by this additional mechanism either.
Interactions With Other Medications
Metoclopramide should not be used with phenothiazine,
tranquilizers such as acepromazine, or if there is any potential for seizures in
the patient. Both medications serve to lower the threshold to seizures.
Propantheline bromide (Pro-Banthine), which is used to
treat some cardiac arrhythmias, will inactivate metoclopramide.
Narcotic analgesics may negate the effects of metoclopramide.
Cautions and Contraindications
In patients with pheochromocytoma (a rare adrenal tumor) the use of
metoclopramide can induce dangerously high blood pressure.
If stomach obstruction is suspected in a patient, it is best not to encourage
motility and some other anti-nausea drug is preferred.
Metoclopramide crosses the placenta and into milk and is probably best
avoided in pregnant or nursing mothers.
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