ONDANSETRON

 

Ondansetron is a selective 5-HT3 receptor antagonist that plays a crucial role in anesthesia and perioperative care. Its primary use is in the prevention and treatment of postoperative nausea and vomiting (PONV), which is a common and unpleasant complication that can occur after surgery. The importance of ondansetron in anesthesia can be highlighted by its various benefits and impact on patient care:

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1. Prevention and treatment of PONV: Ondansetron is highly effective in preventing and treating PONV by blocking the action of serotonin at 5-HT3 receptors in the chemoreceptor trigger zone (CTZ) and the gastrointestinal tract. PONV can cause significant patient discomfort, delay recovery, prolong hospital stays, and increase healthcare costs. Ondansetron helps to reduce these issues by effectively managing PONV.

2. Reduction in the need for rescue antiemetics: The use of ondansetron for PONV prophylaxis can reduce the need for additional rescue antiemetic medications in the postoperative period. This can decrease the potential for side effects and drug interactions associated with multiple antiemetic agents.

3. Chemotherapy-induced nausea and vomiting (CINV) management: Ondansetron is also used to prevent and treat CINV in patients receiving chemotherapy, which may be relevant for patients undergoing surgery for cancer-related conditions. Effective management of CINV can improve patient tolerance of chemotherapy, overall quality of life, and adherence to treatment regimens.

4. Safety profile: Ondansetron is generally well-tolerated, with a favorable safety profile compared to other antiemetic agents. Common side effects are usually mild and include headache, constipation, and dizziness.

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The mechanism of action of ondansetron is primarily related to its ability to block 5-HT3 receptors both centrally and peripherally. Here are the main steps in ondansetron's mechanism of action:

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1. Central action: In the central nervous system, ondansetron selectively blocks 5-HT3 receptors in the chemoreceptor trigger zone (CTZ) of the area postrema in the brainstem. By inhibiting the activation of these receptors, ondansetron reduces the input from the CTZ to the vomiting center, thus decreasing the frequency and severity of nausea and vomiting.

2. Peripheral action: In the gastrointestinal tract, ondansetron blocks 5-HT3 receptors located on vagal afferent nerve terminals. During chemotherapy or radiation therapy, enterochromaffin cells in the gastrointestinal mucosa release serotonin (5-HT), which can activate these vagal afferent nerve terminals through 5-HT3 receptors. By blocking these receptors, ondansetron inhibits the transmission of nausea and vomiting signals from the gastrointestinal tract to the central nervous system.

 

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                                                                                         Key points about Ondansetron

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• Highly effective in decreasing the incidence of postoperative nausea and vomiting (PONV) in susceptible patient population.

 

• Structurally related to serotonin and possesses specific 5-HT3 subtype receptor antagonist properties.

 

• Can cause slight prolongation of QTc interval.

 

• Cardiac arrhythmias (atrioventricular block) have been reported after IV administration of ondansetron and metoclopramide.​

 

• ​The most common reported side effects are headache and diarrhea.

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• Does not alter dopamine, histamine, adrenergic, or cholinergic receptor activity. 

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