ONASERON INJECTION

Indications

• Nausea and vomiting induced by chemotherapy
• Nausea and vomiting induced by radiotherapy
• Postoperative nausea and vomiting
• Prevention of nausea and vomiting in patients undergoing surgery

Dosage

Children: Refer to specific BNF for Children guidelines for dosing information.

Adults: Refer to specific BNF guidelines for dosing information.

Mechanism of action

Ondansetron selectively antagonizes serotonin 5-HT3 receptors, which are involved in the vomiting reflex. By blocking these receptors in both the central nervous system and peripheral nervous system, ondansetron effectively reduces the incidence of nausea and vomiting associated with various medical treatments.

Pharmacodynamics

Ondansetron exhibits a rapid onset of action, typically within 30 minutes when administered intravenously, and can last up to 12 hours. Its efficacy in controlling nausea and vomiting is attributed to its ability to prevent serotonin from binding to the 5-HT3 receptors, thereby interrupting the pathways that trigger vomiting. Ondansetron has a favorable safety profile with minimal side effects, although some patients may experience headache, constipation, or dizziness.

Pharmacokinetics

After oral administration, ondansetron is rapidly absorbed with peak plasma concentrations occurring within 1 to 2 hours. It is extensively metabolized in the liver via cytochrome P450 enzymes, primarily CYP3A4, CYP2D6, and CYP1A2. The elimination half-life ranges from 3 to 6 hours. Ondansetron is eliminated primarily through urine, with approximately 70% of an administered dose excreted as metabolites, while less than 5% is excreted unchanged. Variability in metabolism can occur due to genetic polymorphisms in the CYP enzymes.

Contra-indications

• Hypersensitivity to ondansetron or any of its components
• Concomitant use with apomorphine due to severe hypotension risk

Adverse effects

• Headache
• Constipation
• Diarrhea
• Dizziness
• Fatigue
• Transient visual disturbances
• Hypersensitivity reactions including rash and anaphylaxis

Interactions

• May enhance the effects of serotonergic drugs, increasing the risk of serotonin syndrome
• Concomitant use with drugs that prolong the QT interval should be approached with caution
• CYP3A4 inhibitors may increase ondansetron levels, while CYP3A4 inducers may decrease its effectiveness

Precautions

• Use with caution in patients with electrolyte imbalances, particularly hypokalemia and hypomagnesemia
• Patients with a history of cardiac arrhythmias should be monitored closely
• Caution in patients with liver impairment, as ondansetron is primarily metabolized by the liver

Pregnancy

Ondansetron should only be used in pregnancy if the potential benefit justifies the potential risk to the fetus, as data on its safety during pregnancy is limited.

Breast-feeding

Ondansetron is excreted in breast milk. It is recommended to use caution when administering to breastfeeding mothers.

Storage

Store below 30 degrees Celsius, protect from light. Do not freeze.

Formulations

• Oral tablets
• Oral solution
• Intravenous injection
• Odt (orally disintegrating tablets)