Gastrointestinal Elimination
7.7 Antiemetics
Treatment of nausea and vomiting should be tailored to the cause. There are several medications that work on different neuroreceptors that, when used, can treat nausea and vomiting. For severe cases of vomiting, intravenous fluids may also be needed to treat the accompanying dehydration. [1],[2]
Table 7.7a compares the neurotransmitters involved in the nausea and vomiting process, classes of antiemetic medication targeting these neurotransmitters, prototype antiemetic medications, and associated mechanisms of action.[3] [4][5][6] Each medication class is also discussed in more detail later in this section.
| Neurotransmitter | Medication Class | Antiemetic Drug | Mechanism of Action |
|---|---|---|---|
| Acetylcholine (M1) | Anticholinergics | scopolamine | Blocks ACh receptors in vestibular system |
| Histamine (H1) | Antihistamines | meclizine | Blocks H1 receptors and thus blocks ACh in vestibular system |
| Dopamine (DA2) | Dopamine antagonists | prochlorperazine | Blocks dopamine in CTZ and may block ACh |
| Dopamine and ACh (DA2 and M1) | Prokinetics | metoclopramide | Blocks dopamine in CTZ and stimulates ACh in GI tract |
| Serotonin (5HT) | Serotonin antagonists | ondansetron | Blocks serotonin in GI tract, CTZ, and VC |
| Substance P (NK1) | Neurokinin antagonists | aprepitant | Inhibits substance P neurokinin receptors |
| Cannabinoid (CB1) | Tetrahydrocannabinols (THC) | dronabinol or medical marijuana | Activated CB1 receptor leading to inhibitory effects on cerebral cortex |
Anticholinergics
Scopolamine is an example of an anticholinergic medication that is often used to treat motion sickness or nausea and vomiting associated with surgical recovery from anesthesia and/or opiate analgesia.
Mechanism of Action
Anticholinergics block ACh receptors in the vestibular center and within the brain to prevent nausea-inducing stimuli to the Chemoreceptor Trigger Zone (CTZ) and the Vomiting Center (VC). They also dry GI secretions and reduce smooth muscle spasms.
Specific Administration Considerations
The scopolamine transdermal patch (see Figure 7.7a)[7] is designed for continuous release of scopolamine following the application to an area of intact skin on the head, behind the ear. The system is formulated to deliver approximately 1 mg of scopolamine to the systemic circulation over 3 days. It is contraindicated in clients with glaucoma. It has been reported to exacerbate psychosis, induce seizures, and cause drowsiness, confusion, and sedation. Due to its anticholinergic properties, scopolamine can decrease gastrointestinal motility and cause urinary retention. Nurses should perform more frequent monitoring during treatment with Transderm Scōp and discontinue Transderm Scōp in clients who develop difficulty in urination. Transderm Scōp contains an aluminized membrane; skin burns have been reported at the application site in clients wearing an aluminized transdermal system during an MRI scan. Remo