Ondansetron

Ondansetron is a selective serotonin 5-HT3 receptor antagonist used to prevent nausea and vomiting, particularly those associated with chemotherapy, radiotherapy, and surgery.

5-HT3 receptor: A ligand-gated ion channel activated by serotonin and involved in signaling nausea and vomiting. Ondansetron prevents receptor activation, interrupting serotonin-triggered emetic signals.
Chemotherapy-induced nausea and vomiting: Nausea and vomiting caused by anticancer drug treatment, often managed with preventive antiemetic combinations. Ondansetron is commonly given before emetogenic chemotherapy to reduce acute symptoms.
Metoclopramide: An antiemetic and prokinetic drug that primarily blocks dopamine D2 receptors and also affects serotonin receptors. It offers a different receptor profile and can promote gastric emptying.
Antiemetic: A drug or treatment used to prevent or relieve nausea and vomiting. Ondansetron is one member of this broader therapeutic class.
Torsades de pointes: A potentially life-threatening ventricular arrhythmia associated with prolonged cardiac repolarization. QT prolongation from ondansetron can contribute to this risk in susceptible patients.
Vagus nerve: A cranial nerve carrying sensory information from thoracic and abdominal organs to the brainstem. Blocking 5-HT3 signaling on vagal afferents reduces gut-to-brain emetic transmission.
Postoperative nausea and vomiting: Nausea or vomiting occurring after an operation, influenced by anesthetics, surgery, and patient factors. Ondansetron is used for prevention and treatment after surgery.
Promethazine: A sedating antihistamine with antiemetic effects through histamine and other receptor blockade. Its sedation and receptor actions differ from ondansetron's selective 5-HT3 blockade.
Competitive antagonist: A substance that binds a receptor and competes with an agonist without activating it. Ondansetron competes with serotonin at 5-HT3 receptors.
Congenital long QT syndrome: An inherited disorder of cardiac ion channels that prolongs the QT interval and raises arrhythmia risk. It is a key reason to avoid ondansetron in some patients.

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