Antiemetic and Antinausea Agents

Antiemetic and Antinausea Agents
Chapter 53

Nausea and Vomiting
I Definitions:
A. Nausea: unpleasant feeling that often precedes vomiting
B. Emesis: vomiting. Forcible emptying of gastric, and occasionally, intestinal contents.
C. Antiemetic agents: used to relieve nausea and vomiting
II Pathophysiology
A. Vomiting center (VC): an area in the brain that is responsible for initiating the physiologic events that lead to nausea and vomiting.
B. Chemoreceptor trigger zone (CTZ): sends neurotransmitter signals to the VC.
C. Once the CTZ and VC are stimulated, they initiate the events that trigger the vomiting reflex.
III Neurotransmitter sites in the vomiting pathway
A. ACh acetylcholine: VC in brain, vestibular and labyrinth pathways in inner ear.
B. Dopamine D2: GI tract and CTZ in brain
C. Histamine H2: VC in brain, vestibular and labyrinth pathways in inner ear
D. Prostaglandins PGs: GI tract
E. Serotonin: GI tract, CTZ and VC in brain

Antiemetic Agents
I Anticholinergic agents
A. Mechanism of action
1. Anticholinergic agents: block ACh receptors in the vestibular nuclei and reticular formation
2. bind to and block ACH receptors in the inner ear labyrinth
3. block transmission of nauseating stimuli to CTZ
4. Also block transmission of nauseating stimuli from the reticular formation to the VC
B. Indications
1. motion sicknes
C. Agents
1. scopolamine (ear patch)
II Antihistamine agents:
A. Mechanism of action
1. Block H1 receptors, thereby preventing ACh from binding to receptors in the vestibular nuclei
2. inhibit ACh by binding to H1 receptors
3. prevent cholinergic stimulation in the vestibular and reticular areas, thus preventing N/V.
B. Indications
1. nonproductive cough
2. allergy symptoms
3. sedation
C. Agents
1. dimenhydrinate
2. diphenhydramine
3. meclizine
4. promethazine
III Neuroleptic agents
A. Mechanism of action
1. block dopamine on the CTZ and may also block ACh
B. Indications
1. also used for psychotic disorders
2. intractable hiccups
C. Agents
1. chlorpromazine
2. perphenazine
3. triflupromazine
IV Prokinetic
A. Mechanism of action
1. block dopamine in the CTZ or stimulate ACh receptors in the GI tract
2. Cause CTZ to be desensitized to impulses it receives from the GI tract
3. also stimulate peristalsis GI tract, enhancing emptying of stomach contents
B. Indications
1. GERD
2. delayed gastric emptying
C. Agents
1. metoclopramide
V Serotonin blockers
A. Mechanism of action
1. block serotonin receptors in the GI tract, CTZ and VC
B. Indications
1. N/V for patients receiving chemotherapy and postoperative nausea and vomiting. No other use...just n/v in chemo.
C. Agents
1. dolasetron
2. granisetron
3. ondansetron
VI Tetrahydrocannabinol
A. Mechanism of action
1. have inhibitory affects on the reticular formation, thalamus, and cerebral cortex
2. major psychoactive substance in marijuana
3. inhibitory effects on reticular formation, thalamus, cerebral cortex
4. alter mood and body’s perception of its surroundings
B. Indications
1. N/V associated with chemotherapy, and anorexia associated with weight loss in AIDS pts


VII Nursing Implications
A. Assess complete nausea and vomiting history, including precipitating factors
B. Assess current medications
C. Assess for contraindications and potential drug interactions
D. Many of these agents cause severe drowsiness; warn pts about driving or performing any hazardous tasks
E. Taking antiemetics with alcohol may cause severe CNS depression
F. Teach pts to change position slowly to avoid hypotensive effects
G. For chemo, antiemetics are often given ½ to 3 hours before a chemo agent.
H. Monitor for therapeutic effects
I. Monitor for adverse effects

Many different mechanisms of action.
Most work by blocking one of the vomiting pathways, thus blocking the stimulus that induces vomiting.

Most indications prevent and reduce nausea and vomiting
Side effects stem from their nonselective blockade of various receptors

Can also be used for...

This is used for:
AIDS
Anorexia
etc