Nausea and Vomiting Pharmacotherapy

Vocabulary flashcards covering key terms, drugs, mechanisms, indications, dosing, and adverse effects related to nausea, vomiting, motion sickness, and postoperative nausea management.

Emesis Phase: Nausea

Subjective feeling in throat and epigastrium that signals impending vomiting.

Emesis Phase: Retching

Labored rhythmic contraction of abdominal and thoracic muscles without expulsion of gastric contents.

Emesis Phase: Vomiting

Forceful ejection of stomach contents through the mouth.

Vomiting Center Neurotransmitter Receptors

Muscarinic (ACh), Histaminic (H1), Dopaminergic (D2), Opiate, Serotonergic (5-HT3), Neurokinin (NK1), Benzodiazepine.

Afferent Inputs to Vomiting Center

Chemoreceptor trigger zone (CTZ), cerebral cortex, and visceral afferents from pharynx & GI tract.

Common GI Causes of N/V

Pregnancy, gastric or small-bowel obstruction, IBS, ulcers, reflux, motility disorders, pancreatic/liver disease, infectious gastroenteritis.

Drug Classes Frequently Causing N/V

Chemotherapy agents, opioids, antibiotics, cardiovascular drugs, hormonal therapy, miscellaneous agents (e.g., nicotine, theophylline).

Chemotherapy Drugs Notorious for N/V

Cisplatin, carboplatin, cyclophosphamide, doxorubicin.

Opioids That Induce N/V

Morphine, oxycodone, codeine.

Antibiotics Linked to N/V

Erythromycin, sulfonamides, tetracycline.

Cardiovascular Drugs Causing N/V

β-blockers and calcium-channel blockers.

Hormonal Therapies Causing N/V

Oral contraceptives, estrogen.

Miscellaneous Agents Causing N/V

Nicotine, theophylline, colchicine, iron preparations, amifostine, L-dopa.

First Step in N/V Management

Identify and eliminate the underlying cause.

Goals of N/V Therapy

Treat reversible causes, rehydrate, and restore appetite & oral intake.

Preferred Route When Actively Vomiting

Intravenous administration.

Rectal Route Contraindication

Compromised bowel wall.

Conditions Appropriate for Self-Treatment

Simple upset stomach, motion sickness, pregnancy-associated N/V.

Red Flags Excluding Self-Treatment

Severe, persistent, or repetitive symptoms, or attempts to avoid medical evaluation.

Antacid Onset of Action

5–30 minutes after ingestion.

Timing of Antacid Dosing

Take after meals for best effect.

Magnesium-Containing Antacid ADR

Diarrhea.

Aluminum/Calcium Antacid ADR

Constipation.

Common Antacid Products

Tums (calcium carbonate), milk of magnesia, Mylanta/Maalox (aluminum, magnesium, simethicone), Pepto-Bismol (bismuth subsalicylate).

Simethicone Action

Breaks down gas bubbles in the stomach to relieve bloating.

Motion Sickness Pathophysiology

Disturbance of vestibular input; prevented by blocking H1 and M1 receptors.

Antihistamines for Motion Sickness

Dimenhydrinate 50–100 mg q4-6h, diphenhydramine 25–50 mg q4-6h, meclizine 25–50 mg once daily.

Antihistamine Contraindications

Elderly patients, BPH, or narrow-angle glaucoma due to anticholinergic effects.

Scopolamine Patch Indications

Prevention of motion sickness and postoperative nausea/vomiting (PONV).

Scopolamine Patch Placement Timing

Apply behind the ear at least 4 hours before travel or surgery.

Scopolamine Patch Replacement

Remove after 72 hours, wash site, and apply new patch if continuing therapy.

Histamine-2 Receptor Antagonist MOA

Decrease gastric acid production by blocking H2 receptors on parietal cells.

H2RA Onset and Duration

Onset ≈30 min; duration up to 12 hours.

H2RA Examples

Famotidine, cimetidine, nizatidine.

H2RA Common ADRs

Headache, nausea, diarrhea; possible drowsiness or confusion in elderly.

Oral Rehydration Solution Components

Glucose plus electrolytes (sodium, potassium, chloride).

ORT Brand Examples

Pedialyte, Infalyte, ReVital.

Single-Dose Ondansetron in Children

Reduces vomiting and need for IV fluids in pediatric gastroenteritis.

PONV Risk Factors

Age <50, female sex, non-smoker, history of PONV/motion sickness, hydration status, general anesthesia, volatile agents, nitrous oxide, perioperative opioid use, procedure type/duration.

PONV Risk Stratification

Low (0-1 factors), Moderate (2-3 factors), High (≥3 factors).

First-Line PONV Prophylaxis

Multimodal approach (scopolamine patch, dexamethasone, aprepitant ± low-dose 5-HT3 antagonist).

PONV Rescue in PACU

Give 5-HT3 antagonist; if used prophylactically, switch to different MOA agent.

5-HT3 Receptor Antagonist MOA

Block serotonin binding in CTZ and GI tract to suppress N/V.

Common 5-HT3 Antagonists

Ondansetron, dolasetron, granisetron, palonosetron.

Ondansetron IV Dose Limit

Single dose should not exceed 16 mg due to QT prolongation risk.

5-HT3 Antagonist ADRs

Constipation, headache, asthenia, dizziness, QT prolongation.

Phenothiazine MOA

Block dopamine (D2) receptors in the chemoreceptor trigger zone.

Phenothiazine Uses

Simple N/V and postoperative N/V; suitable for long-term therapy.

Phenothiazine ADRs

Tardive dyskinesia, acute dystonia, hypotension (IV), sedation, neuroleptic malignant syndrome.

Treating Acute Dystonia

Administer diphenhydramine 25–50 mg IV or IM.

Phenothiazine Black Box Warnings

Increased death in dementia patients; promethazine contraindicated in children <2 yrs; IV promethazine may cause severe tissue injury.

Metoclopramide MOA

Blocks dopamine and serotonin receptors in CTZ; enhances GI motility.

Metoclopramide Typical Dose

10–20 mg PO or IV every 6 hours as needed.

Metoclopramide ADRs

Sedation, fatigue, extrapyramidal symptoms, acute dystonia.

Promethazine Suppository Instructions

Insert moistened suppository pointed end first while lying on side; for motion sickness use 30–60 min before travel.