Ondansetron

Ondansetron is a selective serotonin 5-HT3 receptor antagonist primarily used to prevent nausea and vomiting caused by chemotherapy, radiation therapy, and surgery. It works by blocking serotonin receptors in the central nervous system and gastrointestinal tract, which mediate these symptoms.

 

Pharmacokinetics:

  • Half-life is approximately 3 to 4 hours, extending to 6 to 8 hours in the elderly.

  • Metabolized by hepatic cytochrome P450 enzymes, with clearance affected by CYP3A4 inducers (e.g., phenytoin, carbamazepine), though no dose adjustment is typically required.

  • Oral, intravenous, and orally disintegrating tablet formulations are available.

Safety and Adverse Effects:

  • Common adverse effects include headache (about 11%) and constipation (4%).

  • Rare but serious side effects may include QTc interval prolongation (especially with rapid IV infusion or high doses), hypersensitivity reactions, seizures, movement disorders, and liver enzyme elevations.

  • QTc prolongation risk is dose- and infusion-rate dependent; high doses (e.g., 32 mg IV) are contraindicated.

  • Caution in patients with hepatic impairment; total daily dose should not exceed 8 mg in moderate to severe hepatic dysfunction.

  • Limited data in pregnancy and pediatric patients under 3 years; not generally recommended in pregnancy.

Drug Interactions:

  • CYP3A4 inducers can increase ondansetron clearance, but dose adjustments are generally unnecessary.

  • Concomitant use with other QT-prolonging drugs requires caution.

Clinical Use:

  • Effective for prevention of chemotherapy-induced nausea and vomiting (CINV), postoperative nausea and vomiting (PONV), and radiation-induced nausea/vomiting.

  • Well tolerated in clinical trials with over 2,500 patients studied.

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