pms-Ondansetron Overdosage

At present there is little information concerning overdosage with ondansetron. Individual doses of 84 mg and 145 mg and total daily doses as large as 252 mg have been administered with only mild side effects. There is no specific antidote for ondansetron; therefore, in cases of suspected overdosage, symptomatic and supportive therapy should be given as appropriate.
The use of Ipecac to treat overdosage with ondansetron is not recommended as patients are unlikely to respond due to the anti-emetic action of ondansetron itself.
"Sudden blindness" (amaurosis) of 2 to 3 minutes duration plus severe constipation occurred in one patient that was administered 72 mg of ondansetron intravenously as a single-dose. Hypotension (and faintness) occurred in another patient that took 48 mg of oral ondansetron. Following infusion of 32 mg over only a 4-minute period, a vasovagal episode with transient second-degree heart block was observed. Neuromuscular abnormalities, autonomic instability, somnolence, and a brief generalized tonic-clonic seizure (which resolved after a dose of benzodiazepine) were observed in a 12-month-old infant who ingested seven or eight 8 mg ondansetron tablets (approximately forty times the recommended 0.1 to 0.15 mg/kg dose for a pediatric patient). In all instances, the events resolved completely.
Ondansetron prolongs QT interval in a dose-dependent fashion (see Pharmacology: Pharmacodynamics under Actions). ECG monitoring is recommended in cases of overdose.
Cases consistent with serotonin syndrome have been reported in young children following oral overdose.
For management of a suspected drug overdose, contact the regional Poison Control Center.