Products
Ondansetron is commercially available in the form of film-coated tablets, meltable tablets (lingual tablets), as a syrup, and as an infusion/injection preparation. In addition to the original Zofran, generic versions are also available. Ondansetron was introduced in 1991 as the first active ingredient from the group of 5-HT3 receptor antagonists was approved.
Structure and Properties
Ondansetron is present in drugs as ondansetron hydrochloride dihydrate (C18H19N3O – HCl – 2H2O, Mr = 365.9 g/mol), a racemate and white powder that is sparingly soluble in water. Ondansetron is an imidazole, indole, and a carbazole derivative structurally related to serotonin.
Effects
Ondansetron (ATC A04AA01) has antiemetic properties, meaning it is effective against nausea and vomiting. It is a selective and competitive antagonist at serotonin-5-HT3 receptors and active both centrally and peripherally in the digestive tract. Unlike other antiemetics, ondansetron is neither antidopaminergic nor anticholinergic. The half-life is approximately three hours.
Indications
Ondansetron is approved in many countries for the treatment of nausea and vomiting caused by cytotoxic chemotherapy or radiotherapy. It is also approved for the prevention and treatment of nausea and vomiting after surgery.
Dosage
According to the SmPC. Ondansetron can be administered as an infusion, slow intravenous injection, and perorally. Tablets are usually taken twice daily every 12 hours.
Contraindications
- Hypersensitivity
- Combination with apomorphine, because it causes a sharp drop in blood pressure and patients become unconscious.
- The use of ondansetron during pregnancy is not recommended. Malformations have been reported.
For complete precautions, see the drug label.
Interactions
Ondansetron is metabolized by several CYP isozymes, namely CYP3A4, CYP2D6, and CYP1A2. Because different enzymes are available, it is less susceptible to drug-drug interactions. However, strong CYP3A4 inducers may decrease the effects of ondansetron. Other interactions have been described with apomorphine (contraindicated), serotonergic drugs, and tramadol. Ondansetron should be combined with caution with drugs that prolong the QT interval.
Adverse Effects
The most common possible adverse effects include a feeling of warmth, hypersensitivity reactions around the injection site, and headache. Ondansetron may prolong the QT interval in a dose-dependent manner and rarely cause dangerous cardiac arrhythmias. Appropriate precautions must be observed.
