EMITOSS SOLUTION

Indications

• Chemotherapy-induced nausea and vomiting
• Radiotherapy-induced nausea and vomiting
• Postoperative nausea and vomiting
• Nausea and vomiting associated with gastroenteritis

Dosage

Children: Refer to the BNF for Children for specific dosing guidelines for paediatric patients, as doses are determined by the child's age and weight.

Adults: Refer to the BNF for specific dosing guidelines for adults, as dosages vary based on the condition being treated and the patient's response.

Mechanism of action

Ondansetron exerts its antiemetic effects by selectively antagonizing the 5-HT3 receptors located in the central nervous system, particularly in the area postrema of the medulla oblongata and in the gastrointestinal tract. By blocking these receptors, ondansetron inhibits the signaling pathways that lead to the sensation of nausea and the act of vomiting.

Pharmacodynamics

The pharmacodynamics of ondansetron involves its ability to prevent the binding of serotonin at 5-HT3 receptors. This action not only reduces the incidence of chemotherapy-induced nausea and vomiting but also helps manage nausea associated with other medical conditions. Ondansetron has a rapid onset of action, typically within 30 minutes to 2 hours, and its effects can last for several hours, depending on the route of administration.

Pharmacokinetics

Ondansetron is well absorbed after oral administration, with peak plasma concentrations occurring approximately 1-2 hours post-dose. It undergoes first-pass metabolism in the liver and has a bioavailability of about 60-70%. The drug is primarily metabolized by cytochrome P450 enzymes, particularly CYP3A4, CYP2D6, and CYP1A2, and the elimination half-life is approximately 3-6 hours. Ondansetron is excreted mainly in the urine, with a small percentage eliminated unchanged.

Contra-indications

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

Adverse effects

• Headache
• Constipation
• Dizziness
• Fatigue
• Transient visual disturbances
• Hypotension
• QT prolongation
• Serotonin syndrome (when used with other serotonergic agents)

Interactions

• May interact with other medications that prolong the QT interval
• Caution with serotonergic agents, as ondansetron may enhance the risk of serotonin syndrome
• Concomitant use with apomorphine may lead to severe hypotension

Precautions

• Use with caution in patients with a history of cardiac arrhythmias or electrolyte disturbances
• Monitor for signs of serotonin syndrome when used with other serotonergic drugs
• Caution in patients with hepatic impairment, as dose adjustment may be necessary

Pregnancy

Ondansetron should only be used during pregnancy if the potential benefit justifies the potential risk to the fetus.

Breast-feeding

Ondansetron is excreted in breast milk. Caution is recommended when administering to nursing mothers.

Storage

Store below 25 degrees Celsius. Protect from light and moisture. Do not freeze.

Formulations

• Oral tablets
• Oral solution
• Injectable solution