Ondansetron Flashcards
Ondansetron Mechanism of Action
• Ondansetron is an antiemetic.
• Ondansetron antagonises (blocks) serotonin receptors centrally in the brain and peripherally in the gastrointestinal tract, resulting in a reduction in nausea
and vomiting.
Ondansetron Indications
Clinically significant nausea and/or vomiting.
Ondansetron Contraindications
Known severe allergy.
Age less than one year.
Ondansetron Cautions
None
Ondansetron Use in pregnancy
• Safety has not been demonstrated during pregnancy, but ondansetron may be
administered if nausea and/or vomiting is severe.
• May be administered if the patient is breastfeeding. Advise the patient to stop
breastfeeding and seek further advice from their lead maternity carer or GP.
Ondansetron Dose
8 mg IV once for an adult. See the paediatric drug dose tables for a child.
• 4 mg IM for an adult, if IV access cannot be obtained. See the paediatric drug dose tables for a child.
• The IM dose may be repeated once after 20 minutes if required.
• One IV dose may be administered in addition to one IM dose, if clinically significant nausea and/or vomiting persists and IV access is subsequently obtained. For example, in this setting a maximum total dose of 12 mg may be administered to an adult.
Ondansetron Administration
• The preferred route of administration is IV.
• Administer IV undiluted.
• Administer IM undiluted. The preferred site is the lateral thigh as this has the
best absorption. If this site is not suitable use the lateral upper arm.
Ondansetron Common adverse effects
- Headache.
* Flushing.
Ondansetron Onset of effect
- IV: 2-5 minutes.
* IM: 5-10 minutes.
Ondansetron Duration of effect
4-8 Hours
Ondansetron Pharmacokinetics
- Ondansetron is predominantly metabolised by the liver.
* There are no significant effects from liver impairment on acute administration.
Ondansetron Common interactions
• Ondansetron has been reported to prolong the QT interval, particularly if high doses are administered in conjunction with other medicines that also prolong the QT interval, for example erythromycin. However, one or two doses in this
setting is safe.
Ondansetron prophylaxis
• Prophylactic administration of ondansetron is not routinely required. Consider
administering ondansetron if the nature of the patient’s injuries and transport
position are such that vomiting would be particularly problematic.
Ondasetron altered LOC
• Ondansetron should not be administered for vomiting associated with an altered level of consciousness because it is rarely effective in this setting.
