Ondansetron to prevent emesis following N-acetylcysteine for acetaminophen intoxication.

We present a 17-year-old girl who developed persistent vomiting following acetaminophen overdose. Because of the amount of drug ingested (300 mg/kg acetaminophen) and the four-hour postingestion level (256 micrograms/ml), administration of N-acetylcysteine (NAC) was indicated. Emesis occurred immediately following the first three doses of NAC despite administering the drug by continuous nasogastric drip over one hour. Prior to the next attempt, ondansetron (0.15 mg/kg) was administered intravenously as an antiemetic. Thirty minutes following ondansetron, NAC was tolerated without further emesis. Although several antiemetics may have prevented further emesis, we chose ondansetron since, as a serotonin antagonist, it does not cause extrapyramidal side effects or sedation. In patients with potentially toxic drug ingestions, these side effects may be confused with or mask the adverse effects of the ingested drug, thereby interfering with the ongoing evaluation of the patient. Although not previously administered for this indication, ondansetron has several advantages over other antiemetic agents in the setting of an acute drug ingestion.