Antiemetics: Drug Mechanisms, Uses, and Nursing Considerations

Dopamine (D2) Antagonists

Medications that block dopamine (D2) receptors in the CTZ, suppressing emesis signaling.

Prochlorperazine (Compazine)

A dopamine antagonist used for post-op nausea/vomiting, migraine-associated nausea, chemotherapy-induced nausea, and motion sickness.

Adverse effects of Prochlorperazine

Extrapyramidal symptoms (EPS), tardive dyskinesia, orthostatic hypotension, sedation, anticholinergic effects, urine discoloration.

Nursing note for Prochlorperazine

Avoid in elderly patients with dementia-related psychosis; monitor for EPS and hypotension.

Promethazine (Phenergan)

A D2 receptor blocker with CNS depressant and antihistamine activity used for nausea/vomiting and sedation.

Adverse effects of Promethazine

EPS, sedation, orthostatic hypotension, anticholinergic effects, severe tissue injury with IV extravasation.

Nursing note for Promethazine

High-risk IV administration; monitor IV site closely and keep patient supine after IV dose.

Metoclopramide (Reglan)

Blocks dopamine (D2) receptors in CTZ and enhances gastric emptying; used for gastroparesis and GERD.

Adverse effects of Metoclopramide

EPS, tardive dyskinesia, sedation, fatigue, Parkinson-like symptoms, rare seizures.

Nursing note for Metoclopramide

Short-term use only due to risk of irreversible movement disorders; monitor for EPS and excessive sedation.

Serotonin (5-HT3) Antagonists

Medications that block 5-HT3 serotonin receptors in CTZ and GI tract, preventing vagal emetic signaling.

Ondansetron (Zofran)

First-line treatment for chemotherapy-induced and post-operative nausea/vomiting.

Adverse effects of Ondansetron

Headache, constipation or diarrhea, QT prolongation, fatigue.

Nursing note for Ondansetron

Give IV slowly; monitor QT risk and drug interactions.

Hydroxyzine (Vistaril)

An antihistamine that blocks H1 receptors and central cholinergic activity; used for nausea and anxiety-related nausea.

Adverse effects of Hydroxyzine

Sedation, dry mouth, constipation, urinary retention, blurred vision, QT prolongation.

Nursing note for Hydroxyzine

Use caution in older adults; avoid in glaucoma, BPH, asthma.

Dronabinol (Marinol)

A cannabinoid that acts as a CB1 receptor agonist to suppress emetic signaling.

Adverse effects of Dronabinol

Euphoria or dysphoria, dizziness, cognitive impairment, sedation.

Lorazepam (Ativan)

A benzodiazepine that enhances GABA activity to suppress the vomiting center.

Adverse effects of Lorazepam

Sedation, respiratory depression, dependence risk.

Scopolamine (transdermal patch)

An anticholinergic that blocks muscarinic receptors in the vestibular system to inhibit motion-triggered emesis.

Adverse effects of Scopolamine

Blurred vision, dry mouth, drowsiness, confusion.

Nursing note for Scopolamine

Prevent eye exposure after handling; not for acute nausea—prevention only.

Promethazine IV safety risk

Severe tissue injury/necrosis if IV extravasation occurs; prefer deep IM or properly diluted IV with close site monitoring.

Promethazine IV nursing priority

Monitor IV site continuously; stop infusion immediately if pain, swelling, or burning occurs due to risk of tissue damage.

Metoclopramide serious adverse effect

Tardive dyskinesia (can be irreversible; FDA black box warning).

Metoclopramide duration safety rule

Short-term use only due to risk of permanent extrapyramidal movement disorders.

Ondansetron high-risk interaction concern

QT prolongation risk increases with other QT-prolonging drugs or electrolyte abnormalities (low K⁺, low Mg²⁺).

Ondansetron cardiac monitoring concern

Use caution/monitor ECG in patients with arrhythmia risk or electrolyte imbalance due to QT prolongation.

Scopolamine clinical use limitation

Used for motion sickness prevention only; not effective for treating active nausea.

Scopolamine timing rule

Must be applied before exposure (prevention), not as rescue antiemetic.

Hydroxyzine high-risk populations

Avoid/caution in elderly due to anticholinergic effects (confusion, delirium, falls).

Hydroxyzine contraindications (mechanism-based)

Avoid in glaucoma, BPH, asthma due to anticholinergic blockade effects.

Lorazepam antiemetic risk

Respiratory depression and sedation, especially when combined with opioids, alcohol, or other CNS depressants.

Lorazepam key safety teaching

Avoid concurrent CNS depressants due to additive respiratory suppression risk.

Dronabinol safety concern

Causes cognitive impairment, dizziness, and euphoria/dysphoria → increases fall and driving risk.

Dronabinol mechanism-related risk

CB1 agonist effects → psychoactive changes (THC-like intoxication profile).