Ondansetron

Question 1

What is ondansetron?

Answer 1

Ondansetron (4mg/2mL ampule / 4mg ODT) is an antiemetic which works by blocking the action of serotonin.

Metabolised by the liver & excreted by the kidneys.

Question 2

Indications for ondansetron?

Answer 2

1. Significant nausea and/or vomiting

Question 3

Contraindications for ondansetron?

Answer 3

Absolute:

1. Allergy/ADR
2. Congenital long QT syndrome
3. Current apomorphine therapy (used in severe Parkinson’s disease)
4. Patient under 2yrs

Relative:
1. 1st trimester of pregnancy (may only be administered for extreme & uncontrolled hyperemesis)

Question 4

Precautions for ondansetron?

Answer 4

1. Hepatic impairment
2. Elderly patients
3. Intestinal obstruction
4. Patients with risk factors for QT interval prolongation or cardiac arrhythmias (older age, female sex, low left ventricular ejection fraction, left ventricular hypertrophy, ischemia, slow heart rate, and electrolyte abnormalities including hypokalemia and hypomagnesemia)

Question 5

Side effects of ondansetron?

Answer 5

1. Headache
2. Constipation
3. Hypersensitivity reactions including anaphylaxis (rare)
4. ECG changes (rare)

Question 6

What is the dose of ondansetron for an adult?

Answer 6

4-8 mg PO/IM
Total max dose 8 mg
Must not be given within 8 hours of previous ondansetron administration.

4-8 mg IV
Slow push over 2-3 min
Total max dose 8 mg
Must not be given within 8 hours of previous ondansetron administration.

Question 7

What is the dose of ondansetron for a paediatric?

Answer 7

2-4 years
2 mg PO
Single dose only
Must not be given within 8 hours of previous ondansetron administration.

5-12 years
4 mg single dose only
Must not be given within 8 hours of previous ondansetron administration.

IM/IV
Over 2 years
100 microg/kg (rounded up to the nearest 5kg)
Single dose only, cannot exceed 4 mg
Slow push over 2-3 min for IV
Must not be given within 8 hours of previous ondansetron administration.