Anset is a serotonin subtype 3 (5-HT3) receptor antagonist indicated: Prevention of nausea and vomiting associated with initial and repeat courses of emetogenic cancer chemotherapy. Prevention and treatment of post-operative nausea and vomiting. Prevention of radiotherapy-induced nausea and vomiting.

Anti-emetic drugs

Ondansetron is a selective 5-HT3 receptor antagonist. While its mechanism of action has not been fully characterized, ondansetron is not a dopamine-receptor antagonist. Serotonin receptors of the 5-HT3 type are present both peripherally on vagal nerve terminals and centrally in the chemoreceptor trigger zone of the area postrema. It is not certain whether ondansetron's antiemetic action is mediated centrally, peripherally, or in both sites. However, cytotoxic chemotherapy appears to be associated with release of serotonin from the enterochromaffin cells of the small intestine.

Prevention of chemotherapy induced nausea & vomiting (CINV): Adult- Tablet and oral solution: The recommended adult oral dosage of Ondansetron is 24 mg given as three 8 mg tablets in highly emetogenic chemotherapy. In case of moderately emetogenic chemotherapy the oral dose is one 8 mg Ondansetron tablet or 10 ml of Ondansetron oral solution given twice daily. Injection: The recommended i.v. dose of Ondansetron is a single 32 mg dose or three 0.15 mg/kg doses. A single 32 mg dose is infused over 15 minutes beginning 30 minutes before the start of emetogenic chemotherapy. Subsequent doses (0.15 mg/kg) are administered 4 and 8 hours after the first dose of Ondansetron. Suppository: The recommended adult dose is one 16 mg suppository 1-2 hours before treatment. Ondansetron should be continued for upto 5 days after a course of treatment.The recommended dose is one suppository daily. Pediatric patients- Tablet and oral solution: for pediatric patients 4 through 11 years of age the dosage is one 4 mg Ondansetron tablet or 5ml of Ondansetron solution should be administered 3 times a day for 1 to 2 days after completion of chemotherapy. Injection: the dosage in pediatric patients 4 to 18 years of age should three 0.15-mg/kg doses. Suppository:Not recommended. Radiotherapy induced nausea and vomiting: Adult: the recommended oral dosage is one 8mg Ondansetron tablet or 10ml of Ondansetron oral solution given 3 times daily. Post operative nausea & vomiting: Adult- Tablet and oral solution: The recommended dosage is 16 mg given as two 8 mg Ondansetron tablets or 20 ml of Ondansetron oral solution 1hour before induction of anesthesia. Injection: The recommended I.V. dosage of Ondansetron for adults is 4 mg undiluted administered intravenously in not less than 30 seconds, preferably over 2 to 5 minutes, immediately before induction of anesthesia, or postoperatively if the patient experiences nausea and/or vomiting occurring shortly after surgery. Alternatively, 4 mg undiluted may be administered intramuscularly as a single injection for adults. In patients who do not achieve adequate control of postoperative nausea and vomiting following a single, prophylactic, preinduction, I.V. dose of Ondansetron 4 mg, administration of a second I.V. dose of 4 mg Ondansetron postoperatively does not provide additional control of nausea and vomiting. Suppository: The recommended adult dose is one 16 mg suppository 1-2 hours before treatment. Ondansetron should be continued for upto 5 days after a course of treatment.The recommended dose is one suppository daily. Pediatric patients- Injection: The recommended I.V. dosage of Ondansetron for pediatric patients (2 to 12 years of age) is a single 0.1-mg/kg dose for pediatric patients weighing 40 kg or less, or a single 4 mg dose for pediatric patients weighing more than 40 kg. The rate of administration should not be less than 30 seconds, preferably over 2 to 5 minutes. Little information is available about dosage in pediatric patients younger than 2 years of age. Suppository: Not recommended.

Ondansetron does not itself appear to induce or inhibit the cytochrome P-450 drug-metabolizing enzyme system of the liver. Because Ondansetron is metabolized by hepatic cytochrome P-450 drug-metabolizing enzymes, inducers or inhibitors of these enzymes may change the clearance and hence, the half-life of Ondansetron. On the basis of available data, no dosage adjustment of Ondasetron is recommended for patients on these drugs.

Contraindicated in patients known to have hypersensitivity to the drug or any of its components. Concomitant use of apomorphine.

Frequently reported adverse events were headache, constipation and diarrhea, but the majority have been mild or moderate in nature. In chemotherapy-induced nausea and vomiting, rash has occurred in approximately 1% of patients receiving Ondansetron. There also have been reports to a sensation of flushing or warmth, hiccups and liver enzyme abnormalities. Rare cases of anaphylaxis, brochospasm, tachycardia, angina (chest pain), hypokalemia, shortness of breath have also been reported, except for bronchospasm and anaphylaxis, the relationship to Ondansetron is unclear. There have been no evidence to extrapyramidal reactions, in rare case oculogyric crisis appearing alone, as well as with other dystonic reactions without definitive clinical evidence. In case of PONV, with the exception of headache, rates of these events were not significantly different in the Ondansetron and placebo groups.

Pregnancy category B. Reproduction studies at daily oral dose up to 10 and 30 mg/kg/day have been performed in animals and have revealed no evidence of impaired fertility harm to the fetus due to Ondansetron. There are, however, no adequate and well-controlled studies in pregnant women. So the drug should be used in pregnancy only if clearly needed. Ondansetron excretes in milk of lactating animals. Caution should be exercised when Ondansetron is administered to nursing mother.

Hypersensitivity reactions have been reported in patients who have exhibited hypersensitivity to other selective 5-HT3 receptor antagonists. Ondansetron is not a drug that stimulates gastric or intestinal peristalsis. It should not be used instead of nasogastric suction. The use of Ondansetron in patients following abdominal surgery or in patients with chemotherapy-induced nausea and vomiting may mask a progressive ileus and/or gastric distension.

There is no specific antidote for Ondansetron overdose. In addition to the adverse events, hypotension (and faintness) occurred in a patient that took 48 mg of AVONA tablets. In all instances, the events resolved completely.

Store at temperature not exceeding 30ºC in a dry place. Protect from light and moisture.

Anti-emetic drugs

Ondansetron is a potent, highly selective 5HT3 receptor-antagonist. Its precise mode of action in the control of nausea and vomiting is not known. Chemotherapeutic agents and radiotherapy may cause release of 5HT in the small intestine initiating a vomiting reflex by activating vagal afferents via 5HT3 receptors. Ondansetron blocks the initiation of this reflex. Activation of vagal afferents may also cause a release of 5HT in the area postrema, located on the floor of the fourth ventricle, and this may also promote emesis through a central mechanism. Thus, the effect of ondansetron in the management of the nausea and vomiting induced by cytotoxic chemotherapy and radiotherapy is probably due to antagonism of 5HT3 receptors on neurons located both in the peripheral and central nervous system. The mechanisms of action in post-operative nausea and vomiting are not known but there may be common pathways with cytotoxic induced nausea and vomiting.

Carcinogenic effects were not seen in 2-year studies in rats and mice with oral Ondansetron doses up to 10 and 30 mg/kg per day, respectively. Ondansetron was not mutagenic in standard tests for mutagenicity. Oral administration of Ondansetron up to 15 mg/kg per day did not affect fertility or general reproduction performance of male and female rats.Reproduction studies have been performed in pregnant rats and rabbits at daily oral doses up to 15 and 30 mg/kg per day, respectively, and have revealed no evidence of impaired fertility or harm to the fetus due to Ondansetron. There are, however, no adequate and well-controlled studies in pregnant women. Ondansetron is excreted in the breast milk of rats. So caution should be exercised when Ondansetron is administered to a nursing women.