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Antiemetic Agents
Chapter 59

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Nausea and Vomiting
• Most common and most uncomfortable complaints.
• Vomiting is a complex reflex reaction to various stimuli.
• In some cases, it may be desired to induce vomiting.
• In many clinical conditions, the reflex reaction of
vomiting is not beneficial.

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Managing Nausea and Vomiting
• Emetics
– Cause vomiting
– No longer recommended for at-home poison control
• Antiemetics
– Decrease or prevent nausea and vomiting
– Centrally acting or locally acting
– Varying degrees of effectiveness

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Sites of Action of Emetics/Antiemetics

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Groups of Centrally Acting Antiemetics
• Phenothiazines
• Nonphenothiazines
• Anticholinergics/Antihistamines
• Serotonin (5-HT3
) Receptor Blockers
• Substance P/Neurokinin 1 Receptor Antagonists
• Miscellaneous Group

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Phenothiazines
• Actions
– Depresses various areas of the central nervous
system (CNS)
• Indications
– Treatment of nausea and vomiting
• Adverse Effects
– Drowsiness

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Nonphenothiazines
• Actions
– Acts to reduce the responsiveness of the nerve cells
in the CTZ to circulating chemicals that induce
vomiting
• Indications
– Prevention of nausea and vomiting
• Adverse Effects
– Drowsiness
– Fatigue
– Restlessness
– Extrapyramidal symptoms

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Anticholinergics/Antihistamines
• Actions
– Anticholinergics that act as antihistamines and block the
transmission of impulses to the CTZ
• Indications
– Prevention and treatment of nausea and vomiting
• Adverse Effects
– Drowsiness
– Confusion
– Dry mouth
– Anorexia
– Urinary frequency

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Serotonin (5-HT3
) Receptor Blockers
• Actions
– Block those receptors associated with nausea and
vomiting in the CTZ and locally
• Indications
– Control of nausea and vomiting
• Pharmacokinetics
– Rapidly absorbed, metabolized in the liver, and
excreted in urine and feces
• Caution
– Pregnancy and lactation

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Serotonin (5-HT3
) Receptor Blockers
(cont.)
• Adverse Effects
– Headache, drowsiness, myalgia, urinary retention,
constipation, pain at the injection site

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Question
Please answer the following statement as true or false.
Emetic medications are used to induce vomiting and should
be kept in the home in case of an accidental poisoning.

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Answer
False
Rationale: Emetics cause vomiting and are no longer
recommended for at-home poison control.

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Substance P/Neurokinin 1 Receptor
Antagonists
• Actions
– Act directly in the CNS to block receptors associated
with nausea and vomiting
• Indications
– In combination with other agents to prevent nausea
and vomiting
• Pharmacokinetics
– Given orally, metabolized in the liver, and excreted in
urine and feces

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Substance P/Neurokinin 1 Receptor
Antagonists (cont.)
• Adverse Effects
– Anorexia, fatigue, constipation, diarrhea, liver
enzyme elevation, dehydration

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Miscellaneous Antiemetics
• Actions
– Varies with agent
• Indications
– Treatment and prevention of nausea and vomiting
• Pharmacokinetics
– Varies according to agent

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Miscellaneous Agents (cont.)
• Contraindications
– Coma
– Severe CNS depression
– Brain damage or injury
– Hypotension or hypertension
– Severe liver dysfunction

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Miscellaneous Antiemetics (cont.)
• Caution
– Renal dysfunction
– Active peptic ulcer disease
– Pregnancy
– Lactation
• Adverse Effects
– Linked to interference with normal CNS stimulation or
response
• Drowsiness
• Dizziness
• Weakness

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Miscellaneous Antiemetics (cont.)
• Adverse Effects (cont.)
– Photosensitivity
– Hypotension, hypertension, and cardiac arrhythmias
• Drug-to-Drug Interactions
– Alcohol

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Use of Drugs Affecting the Female
Reproductive System Antiemetic Agents
Across the Lifespan

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Prototype Phenothiazines

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Prototype Nonphenothiazines

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Prototype Anticholinergics/
Antihistamines

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Prototype Serotonin (5-HT3
) Receptor
Blockers

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Prototype Substance P/Neurokinin 1
Receptor Antagonists

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Nursing Considerations for Antiemetics
• Assessment: History and Physical Exam
• Nursing Diagnosis
• Implementation
• Evaluation

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Question
What is an anticholinergic antiemetic recommended for
vestibular (inner ear) problems?
A. Granisetron
B. Meclizine
C. Palonosetron
D. Perphenazine

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Answer
B. Meclizine
Rationale: These drugs—buclizine, cyclizine and meclizine -
are anticholinergics that act as antihistamines and block
the transmission of impulses to the CTZ. They are
recommended for the nausea and vomiting associated
with motion sickness or vestibular (inner ear) problems.