Oral Prevent delayed emesis following chemotherapy
Adult: 8 mg bid for up to 5 days after a course
Oral Prophylaxis of chemotherapy-induced nausea and vomiting
emetogenic chemotherapy: 8 mg given 0.5-2 hours prior to chemotherapy, followed by
8 mg after 8 or 12 hours. Highly emetogenic chemotherapy: 24 mg as a single dose, given 0.5-2
hours prior to chemotherapy. Child: Moderately
emetogenic chemotherapy: 4-11 years 4
mg 30 minutes prior to chemotherapy. Repeat dose at 4 and 8 hours after the
initial dose; ≥12-17 years Same as adult
Oral Postoperative nausea and vomiting
Adult: 16 mg given as a single dose 1 hour prior to induction of anaesthesia.
Alternatively, 8 mg 1 hour prior to anaesthesia followed by 2 further
8 mg at 8 hourly intervals. Child: As
oral soluble film: ≥40 kg: 4 mg 1 hour prior to anaesthesia, followed
by another 4 mg dose after 12 hours.
Oral Prophylaxis of nausea and vomiting associated with radiation therapy
Adult: Total body irradiation (TBI): 8 mg 1-2 hours prior to daily fraction of radiotherapy. Single high-dose fraction to the abdomen: 8 mg given 1-2 hours prior to irradiation. Daily fractionated radiation to the abdomen: 8 mg 1-2 hours prior to irradiation, followed by 8 hourly doses repeated daily during the radiotherapy course.
Parenteral Postoperative nausea and vomiting
Adult: 4 mg via slow IV or IM inj given as single dose at induction of anaesthesia. Child: ≥1 month ≤40 kg: 0.1 mg/kg via slow IV inj at anaesthesia induction; >40 kg: 4 mg via slow IV inj as a single dose at induction of anaesthesia. Max: 4 mg/dose.
Parenteral Prophylaxis of chemotherapy-induced nausea and vomiting
Adult: Moderately emetogenic chemotherapy: 8 mg via slow IV inj as a single dose. Alternatively, 0.15 mg/kg via slow IV inj as a single dose. Highly emetogenic chemotherapy: 8 mg via slow IV or IM inj as a single dose immediately prior to treatment, may be followed by either a 1 mg/hour continuous IV infusion for up to 24 hours, or by 2 further doses of 8 mg at 4-hour intervals. Alternatively, 16 mg via IV infusion over at least 15 minutes immediately prior to treatment; or 0.15 mg/kg via IV infusion over 15 minutes, given 30 minutes prior to chemotherapy, may be followed by 2 further doses of 8 mg at 4-hour intervals. Max: 16 mg/dose. Child: ≥6 months 0.15 mg/kg (Max 8 mg) via IV infusion 30 minutes prior to chemotherapy. May repeat dose at 4 and 8 hours after the initial dose. Elderly: <75 years Max: 16 mg via IV infusion over at least 15 minutes; ≥75 years Initially, 8 mg via IV infusion over at least 15 minutes, may be followed by 2 further doses of 8 mg at 4-hour intervals.
Parenteral Prophylaxis of nausea and vomiting associated with radiation therapy
Adult: 8 mg via slow IV or IM inj immediately before treatment. Elderly: ≥75 years Max initial dose: 8 mg via IV infusion over 15 minutes, may be followed by 2 further doses of 8 mg at 4-hour intervals.
Rectal Prevent delayed emesis following chemotherapy
Adult: As supp: 16 mg once daily for up to 5 days after a course of treatment.
Rectal Nausea and vomiting associated with cancer chemotherapy or radiotherapy
Adult: As supp: 16 mg given 1-2 hours prior to treatment.
Special Patient Group
Individuals who have CYP2D6 polymorphism may have altered response to ondansetron, although the reduced enzyme activity in CYP2D6 polymorphism may be normally compensated by other enzymes (CYP3A4, CYP1A2) due to multiple metabolic enzyme pathway.
Genetic testing for CYP2D6 may serve as guide for ondansetron use. However, several factors may cause potential uncertainty of results, including variable allele frequencies among individuals of different ethnicity e.g. CYP2D6*10 is common in Asian population and CYP2D6*17 is common in people with Sub-Saharan African ancestry but has lower prevalence in Caucasians of Europe ancestry. Thus, the alleles that should be tested may vary considerably for a given population.
Ultrarapid metabolisers (carriers of duplicated functional alleles e.g. *1/*1xN, *1/*2xN, *2/*2xN)
May result to increased metabolism of ondansetron leading to reduced antiemetic effect. Select alternative drug not predominantly metabolised by CYP2D6 (e.g. granisetron).
Normal metabolisers (carrying 2 normal function alleles or 2 decreased function alleles or 1 normal function and 1 nonfunctional allele or 1 normal function and 1 decreased function allele or combinations of duplicated alleles that result in an activity score of 1.0–2.0 e.g. *1/*1, *1/*2, *1/*4)
Initiate therapy with recommended starting dose.
Intermediate metabolisers (carriers of 1 decreased function allele e.g. *4/*10, *4/*41) and poor metabolisers (carrriers of nonfunctional alleles only e.g. *3/*4, *4/*4)
Insufficient evidence of demonstrating clinical impact. Initiate therapy with recommended starting dose.
Moderate to severe: Max: 8 mg daily.
May be taken with or without food.
IV infusion: Dilute in 50-100 mL of 5% dextrose in water, 0.9% NaCl or other compatible infusion fluids (e.g. 10% mannitol, Ringer’s solution, 0.3% KCl and 0.9% NaCl, 0.3% KCl and 5% glucose).
Hypersensitivity. Congenital long QT syndrome. Concomitant use with apomorphine.
Patient with hypokalaemia, hypomagnesaemia, CHF, CV conduction abnormalities, bradyarrhythmia, other conditions that may develop prolongation of QT interval or electrolyte abnormalities, phenylketonuria, subacute intestinal obstruction and abdominal surgery. May mask progressive ileus or gastric distension, and occult bleeding in adenotonsillar surgery. Moderate to severe hepatic impairment. Elderly and children. Pregnancy and lactation.
Significant: Chest pain, bradycardia, hypotension, arrhythmia, hypoxia, transient elevation of liver enzymes, transient blurred vision (due to rapid IV inj). Rarely, transient blindness, extrapyramidal symptoms (e.g. dystonic reactions, oculogyric crisis, dyskinesia), seizures, toxic epidermal necrolysis, serotonin syndrome. Gastrointestinal disorders: Constipation, diarrhoea, hiccup, xerostomia, dyspepsia. General disorders and admin site conditions: Malaise, fatigue, fever, cold sensation, injection site reaction, local burning sensation following supp insertion. Investigations: ECG changes. Nervous system disorders: Headache, dizziness, sedation, drowsiness, paraesthesia. Psychiatric disorders: Insomnia, anxiety. Renal and urinary disorders: Urinary retention. Reproductive system and breast disorders: Gynaecological disease. Skin and subcutaneous tissue disorders: Rash, pruritus. Vascular disorders: Flushing, syncope. Potentially Fatal: QT interval prolongation, torsade de pointes. Rarely, liver failure, anaphylaxis and bronchospasm.
IV/Parenteral/PO/Rectal: B (Avoid during 1st trimester due to small increase risk of oral cleft defects.)
Monitor ECG, serum K, and serum Mg. Monitor for signs and symptoms of serotonin syndrome and decreased bowel activity.
Symptoms: Hypotension, visual disturbances, severe constipation, vasovagal episode with transient 2nd degree AV block, and serotonin syndrome characterised by vomiting, diarrhoea, agitation, tachycardia, tremor, seizure, delirium and coma in children. Management: Supportive and symptomatic treatment.
Dexamethasone Na phosphate may potentiate antiemetic effect. May develop serotonin syndrome (including altered mental status, autonomic instability, neuromuscular abnormalities) with SSRIs, MAOIs, mirtazapine, fentanyl, lithium, methylene blue, serotonin noradrenaline reuptake inhibitors (SNRIs). Potent CYP3A4 inducers (e.g. phenytoin, carbamazepine, rifampicin) may reduce plasma concentrations and increase clearance of ondansetron. Coadministration with antiarrhythmics (e.g. amiodarone), atenolol, anthracyclines (e.g. doxorubicin, daunorubicin), trastuzumab, erythromycin, and ketoconazole may cause additive prolongation of QT interval and increase risk of arrhythmia. May decrease analgesic effect of tramadol. Potentially Fatal: Concomitant use with apomorphine may result to profound hypotension and loss of consciousness.
Slightly enhanced extent of absorption with food (tab).
Description: Ondansetron selectively antagonises 5-HT3-receptor on both peripherally on vagal nerve terminals and centrally in the chemoreceptor trigger zone. Onset: Approx 30 minutes. Pharmacokinetics: Absorption: Passively and completely absorbed from the gastrointestinal tract. Slightly enhanced bioavailability with food. Bioavailability: Approx 55-60% (tab). Time to peak plasma concentration: Approx 1.5-2 hours (oral); Approx 10 minutes (IM); Approx 6 hours (rectal). Distribution: Extensively distributed in the body, including erythrocytes. Crosses placenta. Volume of distribution: 1.9 L/kg. Plasma protein binding: Approx 70-76%. Metabolism: Extensively metabolised in the liver mainly via hydroxylation, followed by glucuronide or sulfate conjugation by CYP3A4, CYP1A2 and CYP2D6 isoenzymes. Demethylation may also occur. Excretion: Via urine (44-60%, as metabolites; approx 5% as unchanged drug); faeces (approx 25%). Elimination half-life: Approx 3-6 hours (oral/parenteral); Approx 6 hours (rectal).
Tab: Store between 2-30°C. Oral soluble film: Store between 20-25°C. Protect from moisture. Oral solution, syr: Store between 15-30°C. Protect from light. Do not refrigerate. Supp: Store below 30°C. Vial: Store between 2-30°C. Protect from light.
A04AA01 - ondansetron ; Belongs to the class of serotonin (5HT3) antagonists. Used for the prevention of nausea and vomiting.
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