Ondansetron Flashcards
Ondansetron
Class
Antiemetic
Selective 5-HT3 Receptor Antagonist
Ondansetron
Dose
Adults
Usual dose:
IV: 4 mg as a single dose at the end of surgery (Gan 2014)
OR
Alternative strategy: Oral (oral disintegrating tablet or oral soluble film): 8 mg as a single dose given 30 to 60 minutes prior to surgery (Gan 2014; Grover 2009; Kenny 1992)
For rescue therapy, when should you use Ondansetron again if given for prophylaxis?
> 6 hours since initial dose for most 5-HT3 receptor antagonists
(Feinleib 2018; Gan 2014).
Ondansetron
Renal Impairment: Adult
Dosing Adjustments or Clinical indications?
IV: No dosage adjustment is necessary.
Oral: No dosage adjustment is necessary; however, according to the manufacturer, there is no experience for oral ondansetron in renal impairment beyond first-day administration (has not been studied beyond day 1).
Ondansetron
Hepatic Impairment: Adult
Dosing Adjustments or Clinical indications?
- Mild to moderate impairment: No dosage adjustment necessary.
- Severe impairment (Child-Pugh class C):
IV: Day 1: Maximum daily dose: 8 mg; however, according to the manufacturer, there is no experience beyond first-day administration (has not been studied beyond day 1)
Oral: Maximum daily dose: 8 mg
Ondansetron
Dose
infants and children
≤40 kg: 0.1 mg/kg/dose as a single dose; maximum dose: 4 mg/dose
> 40 kg: 4 mg/dose as a single dose
Ondansetron
Dose
Adolescents
Adolescents: IM, IV: 4 mg/dose as a single dose
When should zofran be administered in peds during surgery?
Administer immediately before or following induction of anesthesia, or postoperatively if the patient is symptomatic.
How effective is repeat dosing of Zofran if N/V uncontrolled?
Repeat doses given in response to inadequate control of nausea/vomiting from preoperative doses are generally ineffective.
1 CNS Side Effect of Zofran
> 10%
Central nervous system:
- Headache (oral: 9% to 27%; IV: 17%)
- Fatigue (oral: ≤9% to 13%)
- Malaise (oral: ≤9% to 13%)
1 GI Side Effect of Zofran
> 10%
Gastrointestinal: Constipation (6% to 11%)
Common CNS Side Effect of Zofran
1-10%
Drowsiness (IV: ≤8%)
Sedation (IV: ≤8%)
Dizziness (7%)
Agitation (oral: ≤6%)
Anxiety (oral: ≤6%)
Paresthesia (IV: 2%)
Sensation of cold (IV: 2%)
Common Dermatological Side Effect of Zofran
1-10%
- Pruritus (2% to 5%)
2. Skin rash (1%)
Common GI Side Effect of Zofran
1-10%
Gastrointestinal:
Diarrhea (oral: 6% to 7%; IV: Children 1 to 24 months of age: 2%)
Common Genitourinary Side Effect of Zofran
1-10%
Genitourinary:
Gynecologic disease (oral: 7%)
Urinary retention (oral: 5%)
Common Hepatic Side Effect of Zofran
1-10%
- Increased serum ALT (>2 times ULN: 1% to 5%; transient)
2. Increased serum AST (>2 times ULN: 1% to 5%; transient)
Zofran
Pregnancy Class
B
No evidence of risk in studies
Either animal reproduction studies have not demonstrated a fetal risk but there are no controlled studies in pregnant women or animal reproduction studies have shown an adverse effect (other than a decrease in fertility) that was not confirmed in controlled studies in women in the first trimester and there is no evidence of a risk in later trimesters.
Zofran
Mechanism of Action
Ondansetron is a selective 5-HT3-receptor antagonist which blocks serotonin, both peripherally on vagal nerve terminals and centrally in the chemoreceptor trigger zone
Zofran
Onset of Action
~30 minutes
Zofran
Adults
Volume of Distribution
Adults: 1.9 L/kg
Zofran
Volume of Distribution
1 to 4 months:
5 to 24 months:
3 to 12 years:
1 to 4 months: 3.5 L/kg
5 to 24 months: 2.3 L/kg
3 to 12 years: 1.65 L/kg
Zofran
Protein Binding
Protein binding, plasma: 70% to 76%
Zofran
Metabolism
Extensively hepatic via hydroxylation, followed by glucuronide or sulfate conjugation;
CYP1A2
CYP2D6
CYP3A4 substrate
Some demethylation occurs
