Antiemetics: a Review

The act of emesis is controlled by the vomiting centre in the medulla, which integrates afferent input from the vestibular system, the chemoreceptor trigger zone (CTZ), the cortex and the gut. Nausea and vomiting induced by several cancer chemotherapy agents is often the most distressing side effect of treatment. The mechanism of action of antiemetic is related to blockage of various type of receptor located in various region of various organ of the body parts. Various drugs are classified under antiemetic like Ondansetron, Granisetron & Metochlopramide etc. A critical review of the studies of aprepitant (a new NK1 receptor antagonist) and of palonosetron (a 5-HT3 receptor antagonist with a longer half-life) presented in this article. Aprepitant combined with dexamethasone and a 5-HT3 antagonist significantly increase the control of acute emesis with respect to dexamethasone. Palonosetron showed superior or similar efficacy to Ondansetron and dolasetron in patients submitted to moderately emetogenic chemotherapy Certain side effects arise due to excessive use of antiemetic like twitching, flushing of skin, headaches, tiredness, indigestion etc. INTRODUCTION: Emesis: It is a forcible emptying of gastric and occasionally intestinal contents due to stimulation of vomiting centre situated in medulla oblongata. The drug agents that provoke emesis are called emetic drugs e.g. apomorphine & ipecacuanha. An individual has consumed certain toxic substances; it must be expelled before absorption by giving emetic drugs. If caustic substances have been ingested there is no need of inducing vomiting e.g. ammonia, chlorine bleach, dye, toilet cleaners, or battery acid. Activated charcoal is given when emesis is due to Cl. Antiemetics: The drug agents that antagonize the action of emetics are called antiemetic drugs. Cisplatin provides an exacting test for anti emetics. This agent at high doses is universally emetic (if anti-emetics are not given) and patients usually experience five or more emetic episodes. IPECAC: It stimulates the CTZ in the medulla & acts directly on the gastric mucosa. Take water (not milk or carbonation) if injested, its onset of action occur in 15 to 30 min. Its toxicity can be cured by giving charcoal. The toxicity indications of ipecac are hypotension, tachycardia, chest pain, diarrhea, sedation, lethargy etc 1, . CINV (Chemotherepy induced Nausea and Vomiting) Clasification: There are clinically 5 distinct forms of Chemotherapy Induced Nausea and Vomiting (CINV): acute, delayed, anticipatory, break through and refractory.