Chapter 162-Antiemetics and Prokinetics Flashcards
Maropitant
- Antiemetic
- Neurokinin-1 Receptor Antagonist (NK-1), which blocks the action of substance P in the CNS as well as at peripheral NK-1 receptors in the GIT
- SE- bone marrow hypoplasia when adminsitered to puppies <11 weeks old
- First-pass metabolism (higher bioavailability when given SQ/IV then PO)
- Other possible effects include- antiinflamamtory, neuroproectant, hepatoprotectant, antitumor.
- Will decrease visceral pain and reduce MAC during anesthesia (IV)
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Ondansetron (+ granisetron, dolasetron)
- Antiemetic
- 5-HT3 Receptor Antagonists, competatively blocks seratonin (5-HT3) receptors which are both found peripherally (intestinal vagal afferent input- many in the GIT) and centrally (in the CRTZ) and meduallary vomiting center (MVC)
- Metabolized by the liver [Dolansetron is metabolized to the active form (hydrodolasetron) by ubiquitous carbonyl reductase}
- Eleminated by hepatic P-450, then in urine and bile
- Ondansetron will decrease the efficacy of tramadol
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Metoclopramide
- Antiemetic/Prokinetic
- MOA: antidopaminergic activity and blocks 5-HT3 receptros = blocker of CRTZ (less effective in cats due to the dopamine receptors portion of action).
- Prokinetic activity increases gastric emptying and decrease gastroesophageal reflux
- Prokinetic effects may also be because of incresed sensitivity of the smooth muscle in the small intestins to the effects of acetylcholine
- Better as CRI, light sensative
- Excerted by kidneys
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Promazine Derivatives
(Chlorpromazine, Prochlorperazine, Acepromazine)
- Antiemitic
- MAO- broad spectrum, centrally acting antiemtics (effective against all but inner ear disease). Antidopaminergic and antihistamine effects that block the CRTZ (MVC at higher doses). Aslo have anticholinergic, antispasmodic and alpha-adrenergic blocking effects
- SE: vasodilation/hypotension (due to the aplpha-adrenergic blockage), may also increace CVP and change heart rate +/- arrythmias (dog)
- Metabolized by liver (can cause CNS side effects if hepatic insufficiency- especially with PSS)
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Anticholinergic Agents
(Aminopentamide)
- Antiemetic
- MOA: anticholinergic- there are cholinergic recptors in the brain involved in the vomiting center and in the upper GIT via the vagus nerve (muscarinic receptors)
- Less effective then metoclopramide and far inferior than 5-HT3 and NK-1 antagonists
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Trimethobenzamide
- Antiemetic
- MOA: antidopamiinergic properties
- Weak antiemetic in dogs
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Steroids as antiemetics?
- Often used in human chemo patients
- May have some effect- think of the IBD cat
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Other (less common) antiemetics?
1) Megestrol acetate
2) Gabapentin
3) Propofol
4) Acupuncture
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Peripherally acting antiemetics
- Soothe inflammed mucosal lesions - ex- bismuth subsalicylate or barium sulfate
- decrease dyspepsia (or indigestion)- ex) antacid or gastric acid reducing drugs
Overall much less effective
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Cisapride
- Prokinetic
- MOA: 5-HT4 serotonergic agonist (the most effective prokinetic class in vetmed) to increase gastric emptying and to increase gastroesophageal sphincter pressure (it is ineffective on striated muscle), also increase small intestinal motility
- Tx: GE reflux, decreased gastric emptying, chronic constipation
- Well absorbed, first-pass metabolism via liver
Japan (Mosapride)- can go IV, less colon effects
Europe (Tegaserod) - increases colonic motility
Europe (Prucalopride)- increases colonic and gastric motility
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Cholinomimetic Drugs
(Bethanechol, ranitidine, nizatidine)
-Prokinetic, specifically colon
Bethanechol- binds muscarinic receptors to effect receptors throughout the GIT
Ranitidine/Nizatidine- inhibit acetylcholinesterace, better at gastric then colonic motility
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Erythromycin
- Prokinetic, AB
- MOA: stimulates motilin receptors to promote GI motility, also increases lower esophageal sphincter pressure and increases large and small intestinal peristalsis
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Antiemetic Chart
