04 Antiemetics and Prokinetic Agents for Nausea, Vomiting, and Motility Disorders Flashcards
What is the primary difference between antiemetics and prokinetic agents?
Antiemetics are used to treat nausea and vomiting, while prokinetic agents enhance gastroduodenal motility and accelerate gastric emptying.
What are the major uses of 5-HT3 receptor antagonists like ondansetron?
They are used to control chemotherapy-induced vomiting, postoperative vomiting, and other drug-induced vomiting, excluding motion sickness.
How do dopamine D2 antagonists like metoclopramide and domperidone prevent vomiting?
They block D2 receptors in the chemoreceptor trigger zone (CTZ), enhancing lower esophageal sphincter tone and promoting gastric peristalsis.
What precaution should be taken when prescribing dolasetron?
Dolasetron can prolong the QT interval and should be avoided in patients with a prolonged QT interval.
Why is domperidone preferred over metoclopramide in certain cases?
Domperidone does not cross the blood-brain barrier, reducing the risk of extrapyramidal and neuropsychiatric side effects.
What mechanism underlies the prokinetic effects of metoclopramide?
Metoclopramide acts via D2 receptor blockade and 5-HT4 receptor agonism to enhance acetylcholine release, promoting gastric peristalsis and emptying.
What serious side effects led to the ban of cisapride in many countries?
Cisapride can cause serious cardiac arrhythmias, including QT prolongation, ventricular tachycardia, and atrial fibrillation, especially with enzyme inhibitors.
What are the adverse effects associated with metoclopramide?
Sedation, restlessness, anxiety, diarrhea, gynecomastia, galactorrhea, and extrapyramidal symptoms like tardive dyskinesia and parkinsonism.
What role do corticosteroids play in antiemetic therapy?
Corticosteroids like dexamethasone are combined with other antiemetics to control delayed vomiting following anticancer drug therapy.
How does erythromycin function as a prokinetic agent?
Erythromycin acts as a motilin receptor agonist, promoting motility in the upper gastrointestinal tract, and is used in diabetic gastroparesis.
A patient undergoing chemotherapy is experiencing severe vomiting. What combination of drugs could be prescribed for optimal control?
A 5-HT3 antagonist (e.g., ondansetron), a neurokinin receptor antagonist (e.g., aprepitant), and a corticosteroid (e.g., dexamethasone).
Why might hyoscine be preferred for motion sickness over other antiemetics?
Hyoscine, an antimuscarinic, effectively reduces vestibular overstimulation and relaxes gastrointestinal smooth muscle, making it particularly suited for motion sickness.
What makes palonosetron a superior choice among 5-HT3 antagonists?
Palonosetron has a higher affinity for 5-HT3 receptors and a longer half-life, providing prolonged antiemetic effects.
A pregnant patient presents with morning sickness. What is a safe antiemetic option?
Pyridoxine (vitamin B6) or doxylamine, often combined with pyridoxine in some countries, is commonly used, though safety profiles vary by region.
How does domperidone differ from metoclopramide in treating nausea and vomiting?
Domperidone does not cross the blood-brain barrier, minimizing central side effects like extrapyramidal symptoms, while still acting on CTZ dopamine receptors.
