Chapter 30 The mechanisms of action for these first two classes of drugs are not discussed in detail because drugs with similar mechanisms of action can be found in other chapters. The use of these drugs as antiemetics is discussed in this chapter (see Table 30-1). The phenothiazine subclass of the antidopaminergic antipsychotics includes prochlorperazine and promethazine, which are used for nausea and vomiting. See Chapter 49 for a detailed discussion of the phenothiazine antipsychotics. The anticholinergics are divided into two subclasses. The antihistamines commonly used as antiemetics are meclizine and dimenhydrinate. See Chapter 15 for a detailed discussion of antihistamines. The other subclass of anticholinergics includes trimethobenzamide and scopolamine. These are similar to other anticholinergics, which are discussed in detail in Chapter 31. The serotonin 5-hydroxytryptamine3 (5-HT3) receptor antagonists are most useful for the prevention of chemotherapy-induced emesis (CIE) and are discussed in Chapter 31. The prokinetic agent, metoclopramide, is also discussed in Chapter 31. A “vomiting center” (VC) in the medulla coordinates the respiratory and vasomotor centers and vagus nerve innervation of the GI tract. This center may have four different sources of stimuli. The chemoreceptor trigger zone (CTZ) is located outside the blood-brain barrier near the vomiting center in the medulla (Table 30-2). It communicates with the vomiting center after input is received from drugs and hormones. TABLE 30-2 Sources of Stimuli to the Vomiting Center Antiemetics act on the VC in the medulla through the four different sources of stimuli input. See Table 30-2.
Antiemetics
Class
Subclass
Generic Name
Trade Name
Antidopaminergics
Phenothiazines
prochlorperazine
Compazine
promethazine
Phenergan
Benzamides
metoclopramide
Reglan
trimethobenzamide HCl
Tigan
Anticholinergics
Antihistamines
meclizine
Antivert
dimenhydrinate
Dramamine
scopolamine
Transderm-Scop
Scopace
NK1 Receptor antagonists
aprepitant
Emend
Serotonin 5-HT3 receptor antagonists
ondansetron HCl
Zofran
dolasetron
Kytril
granisetron HCl
Aloxi
palonosetron
Therapeutic Overview
Anatomy and Physiology
Source of Stimuli
Type of Stimulus
Receptors Involved
GI tract: afferent vagal and splanchnic fibers
Distention, irritation, infection, obstruction, dysmotility
Vagal: 5-HT3
Vestibular system
Motion, infection
Histamine1 (H1) and muscarinic, cholinergic
Higher CNS centers
Increased intracranial pressure, infection, tumor, hemorrhage
Psychogenic: sights, smells, emotions
Various
Chemoreceptor trigger zone (located outside the blood-brain barrier near the medulla)
Drugs such as opioids, chemotherapy, toxins, hypoxia, uremia, acidosis, and radiation therapy
5-HT3 and dopamine D2
Mechanism of Action
< div class='tao-gold-member'>
Stay updated, free articles. Join our Telegram channel
![](https://clinicalpub.com/wp-content/uploads/2023/09/256.png)
Full access? Get Clinical Tree
![](https://videdental.com/wp-content/uploads/2023/09/appstore.png)
![](https://videdental.com/wp-content/uploads/2023/09/google-play.png)