Nausea & Vomiting Study Notes

Nausea & Vomiting Overview

  • Nausea: Unpleasant feeling that often precedes vomiting.

  • Vomiting (emesis): Forcible expulsion of gastric and intestinal contents through the mouth.

Physiology

  • Chemoreceptor trigger zone sends neurotransmitter signals to the vomiting center to trigger the vomiting reflex.

Classes of Antiemetics

  • Anticholinergics

  • Antihistamines (H1 receptor blockers)

  • Antidopaminergic drugs

  • Neurokinin antagonists

  • Prokinetic drugs

  • Serotonin blockers

  • Tetrahydrocannabinoids

Anticholinergics

  • Mechanism: Block acetylcholine effects, reducing vomiting.

  • Medications:

    • Trimethobenzamide (Tigan) - PO, PR, IM

    • Scopolamine (Scopace, Transderm-Scop) - IV, SC, transdermal

  • Side Effects: Drowsiness, dry mouth, urinary retention, constipation.

  • Contraindications: Closed-angle glaucoma.

Antihistamines (H1 Receptor Blockers)

  • Medications:

    • Meclizine (Antivert, Bonine) - OTC

    • Promethazine (Phenergan) - PO, IV, IM, PR

    • Hydroxyzine (Vistaril)

  • Indications: N/V, motion sickness, allergy symptoms, vertigo.

  • Side Effects: Dizziness, dry mouth, urinary retention.

Antidopaminergic Drugs (Phenothiazines)

  • Mechanism: Block dopamine receptors in the vomiting center.

  • Medications:

    • Prochlorperazine (Compazine)

    • Promethazine (Phenergan)

  • Side Effects: Orthostatic hypotension, extrapyramidal symptoms, sedation.

Prokinetic Drugs

  • Mechanism: Block dopamine receptors in chemoreceptor trigger zone, stimulate GI peristalsis.

  • Medication: Metoclopramide (Reglan).

  • Side Effects: Hypotension, sedation, fatigue.

Serotonin Antagonists

  • Function: Prevent N/V associated with chemotherapy by blocking serotonin.

  • Medication: Ondansetron (Zofran).

  • Administration: 30 minutes prior to surgery or chemotherapy.

  • Side Effects: Headache, diarrhea, bronchospasm.

Neurokinin Blockers

  • Mechanism: Inhibit substance P-Neurokinin receptors.

  • Medication: Aprepitant (Emend).

  • Side Effects: Drowsiness, hypotension, diarrhea.

Tetrahydrocannabinoids

  • Function: Inhibitory effects on vomiting; stimulate appetite.

  • Medication: Dronabinol (Marinol).

  • Side Effects: Drowsiness, anxiety, confusion.

Patient Education

  • Antiemetics may cause drowsiness.

  • Educate about adverse effects.

  • Administer antiemetics 30-60 minutes before chemotherapy.

Nutritional Considerations

  • Nutritional supplements (e.g., Boost, Ensure) can help improve nutritional status in patients experiencing N/V.