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Pharmacology of ondansetron
1School of Pharmacy, University of Bradford, West Yorkshire, UK.
Abstract:
Ondansetron is a highly potent and selective antagonist at 5-HT3 receptors. Its anti-emetic actions were first revealed by its ability to antagonize retching and vomiting induced by chemotherapy and radiotherapy in animals and man. Subsequently, the availability of labelled 5-HT3 receptor ligands allowed identification of 5-HT3 receptors, located at highest densities in the area postrema, nucleus tractus solitarius (NTS), in other areas of the brain, and on afferent terminals of the vagus nerve. Postoperative nausea and vomiting may be caused by various factors: the anaesthetic, associated drugs, the surgical procedure, movement of the patient, sex, weight and pain. These factors mediate their effects via the higher brain circuits, the vestibular nuclei, the chemoreceptor trigger zone in the area postrema, or the upper gastrointestinal tract via the vagus nerve, influencing motor and visceral emetic outputs in the hind-brain. It is hypothesized that ondansetron blocks nausea and vomiting by 5-HT3 receptor antagonism at two specific sites: (i) centrally, in the area postrema/NTS; and (ii) peripherally on vagus nerve terminals. The absence of other pharmacological effects of ondansetron ensures an absence of side-effects.
Insights
Ondansetron effectively blocks nausea and vomiting by targeting serotonin 5-HT3 receptors. This anti-emetic action occurs both centrally in the brain and peripherally on nerve terminals, with minimal side effects.
Area of Science:
- Pharmacology
- Neuroscience
- Gastroenterology
Background:
- Ondansetron is a potent and selective 5-HT3 receptor antagonist.
- Its anti-emetic properties were initially observed in chemotherapy and radiotherapy models.
- 5-HT3 receptors are densely located in the area postrema, nucleus tractus solitarius (NTS), and vagus nerve afferent terminals.
Purpose of the Study:
- To elucidate the mechanism of action of ondansetron in preventing nausea and vomiting.
- To identify the specific sites where ondansetron exerts its anti-emetic effects.
Main Methods:
- Review of existing literature on ondansetron's pharmacology and receptor binding.
- Analysis of the neuroanatomical distribution of 5-HT3 receptors.
- Hypothesizing ondansetron's mechanism based on receptor antagonism.
Main Results:
- Ondansetron antagonizes 5-HT3 receptors, mediating its anti-emetic effects.
- Receptor antagonism occurs both centrally (area postrema/NTS) and peripherally (vagus nerve terminals).
- The drug's selectivity for 5-HT3 receptors correlates with an absence of other pharmacological side-effects.
Conclusions:
- Ondansetron's anti-emetic efficacy is attributed to 5-HT3 receptor blockade at key central and peripheral sites.
- This targeted mechanism contributes to its favorable safety profile with minimal side-effects.