6B. Nausea and Vomiting Overview

Nausea and Vomiting Overview

• Nausea is an unpleasant feeling of impending vomiting, often accompanied by pallor and increased saliva. It's triggered by mediator release (e.g., 5-HT) from enterochromaffin cells in the digestive tract.
• Vomiting (emesis) is the forceful expulsion of stomach contents, involving spasmodic contractions of the stomach, esophagus, and abdominal muscles.
• Sialorrhea is excessive saliva production.
• Several factors, both intraperitoneal (e.g., infections, IBD, motility issues) and extraperitoneal (e.g., heart conditions, cancer, infections, metabolic issues, psychological causes), can cause nausea and vomiting.
• Chemotherapy, certain medications, and pregnancy are other potential triggers.

Vomiting Center and Process

• The vomiting center is located in the nucleus of the tractus solitarius and coordinates the vomiting reflex.
• This involves intricate actions from the throat, digestive system, and abdominal muscles.
• The process has distinct phases: pre-expulsion (gastric relaxation), retching (respiratory muscle contraction), and expulsion (strong abdominal muscle contractions and esophageal sphincter relaxation).
• Multiple pathways (gut, CTZ), brain regions, and sensory input can activate the vomiting center.

Causes and Treatment

• Diagnosis involves a comprehensive history and physical examination to determine the cause.
• Treatment focuses on addressing underlying conditions.
• Metabolic imbalances (e.g., hypokalemia, hypochloremia, metabolic alkalosis) are common complications of severe vomiting which should be corrected.
• Antiemetic therapy is administered based on the cause.

Antiemetic Medications

5-HT3 Receptor Antagonists (e.g., Ondansetron, Granisetron)

• Mechanism: Block 5-HT3 receptors.
• Uses: Chemotherapy, radiotherapy, and post-operative nausea/vomiting.
• Side effects: Headaches, constipation, prolonged QT interval.

Dopamine Receptor Antagonists (e.g., Prochlorperazine, Metoclopramide)

• Mechanism: Block dopamine receptors; Metoclopramide also increases gastric emptying & lower esophageal sphincter tone.
• Uses: Nausea/vomiting, gastroparesis (e.g., diabetic), persistent GERD.
• Side effects: Extrapyramidal symptoms, hyperprolactinemia, and other potential reactions.

NK1 Receptor Antagonists (e.g., Aprepitant, Fosaprepitant)

• Mechanism: Block substance P (NK1) receptors.
• Uses: Chemotherapy-induced nausea/vomiting.
• Side effects: Fatigue and gastrointestinal issues.

H1 Receptor Antagonists (e.g., Cinnarizine, Dimenhydrinate)

• Mechanism: Block histamine H1 receptors.
• Uses: Motion sickness and nausea.
• Side effects: Drowsiness and other potential responses.

Additional Antiemetic Agents

• Anticholinergic Drugs (e.g., Scopolamine): Used mainly for motion sickness and post-op nausea/vomiting, affecting acetylcholine receptors.
• Neurokinin Antagonist (e.g., Aprepitant):
• Cannabinoids (e.g., Dronabinol): A synthetic cannabinoid used for anorexia associated with weight loss, for nausea associated with chemotherapy.
• The synthetic cannabinoid can trigger a hyperemesis syndrome.

Chemotherapy-Induced Nausea/Vomiting (CINV)

• Different chemotherapy regimens have varying emetic potential.
• Treatment strategies are tailored based on emesis risk factors.

Pregnancy-Related Nausea/Vomiting

• Antihistamines (e.g., H1 antagonists, doxylamine, meclizine) often are safe for use in treating morning sickness.

General Note

• All medication use should be discussed with a healthcare professional.