Ondansetron

A selective serotonin receptor antagonist used to prevent nausea and vomiting.

What is Ondansetron?

Ondansetron is a 5-HT₃ (serotonin) receptor antagonist used primarily as a powerful antiemetic.

It is highly effective in chemotherapy, radiotherapy, and postoperative nausea.

History & Background

Ondansetron was a breakthrough drug in cancer care, significantly improving quality of life by preventing severe vomiting.

Chemical Structure & Properties

• IUPAC name: (RS)-9-methyl-3-[(2-methylimidazol-1-yl)methyl]-2,3-dihydro-1H-carbazol-4-one
• Molecular formula: C₁₈H₁₉N₃O
• Molar mass: 293.36 g/mol
• Functional groups: Indole, ketone

Mechanism of Action

Ondansetron blocks 5-HT₃ receptors located in:

• Gastrointestinal tract
• Vomiting center (medulla)
• Chemoreceptor trigger zone

This prevents serotonin-mediated nausea and vomiting.

Pharmacokinetics

• Absorption: Rapid oral absorption
• Peak plasma time: 1.5–2 hours
• Metabolism: Liver (CYP3A4, CYP2D6)
• Half-life: 3–6 hours
• Excretion: Urine and feces

Medical Uses

• Chemotherapy-induced nausea and vomiting
• Postoperative nausea
• Radiotherapy-induced vomiting
• Acute gastroenteritis (off-label)

Dosage Guidelines

Adults: 4–8 mg every 8–12 hours

IV use: Hospital settings

⚠️ Maximum single IV dose: 16 mg.

Side Effects

• Headache
• Constipation
• Dizziness
• QT interval prolongation

Warnings & Precautions

• Avoid in congenital long QT syndrome
• Use caution with heart disease
• Electrolyte imbalance increases risk

Drug Interactions

• Other QT-prolonging drugs
• SSRIs and SNRIs
• Apomorphine (contraindicated)

Frequently Asked Questions

Is ondansetron a painkiller? – No.

Does it cause sleep? – Rarely.

Can it be used in pregnancy? – Only if prescribed.

Is it strong? – Yes, very effective antiemetic.

⚠️ Educational content only. Not a substitute for professional medical advice.