Pharmacologic Profile

General Use

Phenothiazines, dolasetron, granisetron, metoclopramide, ondansetron, and palonosetron are used to manage nausea and vomiting of many causes, including surgery, anesthesia, and antineoplastic and radiation therapy. Aprepitant, fosaprepitant, netupitant, and rolapitant are used specifically with emetogenic chemotherapy. Dimenhydrinate, scopolamine, and meclizine are used almost exclusively to prevent motion sickness.

General Action and Information

Phenothiazines act on the chemoreceptor trigger zone to inhibit nausea and vomiting. Dimenhydrinate, scopolamine, and meclizine act as antiemetics mainly by diminishing motion sickness. Metoclopramide ↓ nausea and vomiting by its effects on gastric emptying. Dolasetron, granisetron, palonosetron, and ondansetron block the effects of serotonin at 5-HT₃ receptor sites. Aprepitant, fosaprepitant, netupitant, and rolapitant act as selective antagonists at substance P/neurokinin 1 receptors in the brain.

Contraindications

Previous hypersensitivity.

Precautions

Use phenothiazines cautiously in children who may have viral illnesses. Use dolasetron, granisetron, palonosetron, and ondansetron with caution in patients with QT interval prolongation. Choose agents carefully in pregnant patients (no agents are approved for safe use).

Interactions

Additive CNS depression with other CNS depressants including antidepressants, antihistamines, opioid analgesics, and sedative/hypnotics. Phenothiazines may produce hypotension when used with antihypertensives, nitrates, or acute ingestion of alcohol.

Nursing Implications

Assessment

• Assess nausea, vomiting, bowel sounds, and abdominal pain before and following administration.
• Monitor hydration status and intake and output. Patients with severe nausea and vomiting may require IV fluids in addition to antiemetics.

Potential Nursing Diagnoses

• Deficient fluid volume (Indications)
• Imbalanced nutrition: less than body requirements (Indications)
• Risk for injury (Side Effects)

Implementation

• For prophylactic administration, follow directions for specific drugs so that peak effect corresponds to time of anticipated nausea.

Patient/Family Teaching

• Advise patient and family to use general measures to decrease nausea (begin with sips of liquids and small, nongreasy meals; provide oral hygiene; and remove noxious stimuli from environment).
• May cause drowsiness. Advise patient to call for assistance when ambulating and to avoid driving or other activities requiring alertness until response to medication is known.
• Advise patient to make position changes slowly to minimize orthostatic hypotension.

Evaluation/Desired Outcomes

• Prevention of, or decrease in, nausea and vomiting.