Chapter 41: Antiemetic & Antinausea Drugs

Chapter 41 details the pharmacological management of nausea and vomiting, known collectively as emesis, focusing on the antiemetic drugs used in Canadian health care practice. The physiological events leading to vomiting are governed by two key brain areas: the Vomiting Centre (VC) and the Chemoreceptor Trigger Zone (CTZ). These centers are activated by various stimuli and specific neurotransmitters, including acetylcholine (ACh), dopamine (D2), histamine (H1), and serotonin (5-HT3). Antiemetic effectiveness is increased when combining drugs from the six major categories, each blocking different pathways. These categories include Anticholinergics (e.g., scopolamine), Antihistamines, Antidopaminergics (e.g., promethazine, prochlorperazine), Prokinetics (e.g., metoclopramide), Serotonin Blockers (e.g., ondansetron, granisetron), and Tetrahydrocannabinol (THC). Serotonin blockers, which target 5-HT3 receptors in the GI tract, CTZ, and VC, are particularly effective for chemotherapy-induced and postoperative nausea. Adjunctive therapies include neurokinin-1 receptor antagonists (aprepitant), which augment the effects of steroids and serotonin blockers, as well as corticosteroids and anxiolytics like lorazepam, which helps reduce anticipatory nausea. Critical nursing responsibilities involve thorough baseline assessment of hydration and electrolyte status, careful administration (noting that high-alert drugs like promethazine require specific routes to prevent tissue damage, and long-term use of metoclopramide poses a risk of tardive dyskinesia), and patient education regarding common adverse effects like sedation and the need to avoid CNS depressants. Prophylactic dosing, typically administered 30 to 60 minutes before stimuli like chemotherapy, is key to maximizing therapeutic outcomes.