Ondansetron is indicated for • Prevention of nausea & vomiting associated with highly emetogenic cancer chemotherapy • Prevention of nausea & vomiting associated with radiotherapy • Prevention of post operative nausea & vomiting
5-HT3 receptor antagonist; Antiemetic
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.
Prevention of chemotherapy induced nausea & vomiting (CINV): Adult- 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 Pediatric patients- for pediatric patients 4 through 11 years of age the dosage is one 4mg tablet or 5ml of solution should be administered 3 times a day for 1 to 2 days after completion of chemotherapy. Radiotherapy induced nausea & vomiting: Adult- the recommended oral dosage is one 8mg tablet or 10ml of oral solution given 3 times daily. Post operative nausea & vomiting (PONV): Adult- the recommended dosage is 16 mg given as two 8mg tablets or 20 ml of oral solution 1hour before induction of anesthesia. Dosage adjustment for patients with impaired hepatic function- The total daily dose of 8mg should not be exceeded.
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.
Ondansetron is contraindicated in patients with known hypersensitivity to the drug. Hypersensitivity reactions have been reported in patients who have exhibited hyper sensitivity to other 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 & vomiting may mask a progressive ileus and/or gastric distension.
Headache, malaise/fatigue, constipation; drowsiness, fever, dizziness, anxiety, cold sensation; pruritus, rash; diarrhoea; gynaecological disorder, urinary retention; elevated transaminase; local inj site reaction (pain, redness, burning); paresthesia; hypoxia. Rarely: Anaphylaxis, angina, brorichospasm, ECG changes, extrapyramidal symptoms, grand mal seizure, hypokalaemia, tachycardia, vascular occlusive events.
In pregnancy: Pregnancy category B. So the drug should be used in pregnancy only if clearly needed. In lactation: Ondansetron excretes in milk of lactating animals. Caution should be exercised when Ondansetron is administered to nursing mother.
Store at temperature not exceeding 30ºC in a dry place. Protect from light and moisture.
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