Effect of metoclopramide dose on preventing emesis after oral administration of N-acetylcysteine for acetaminophen overdose

Objective: To determine the effect of the metoclopramide dose on the prevention of vomiting of N-acetylcysteine in acetaminophen overdose. Methods: Patients with acetaminophen ingestions receiving metoclopramide prior to emergency department administration of N-acetylcysteine were included. Emergency Department and poison center records were reviewed for administration of metoclopramide pre-N-acetylcysteine and incidence of subsequent vomiting. The treatment group was defined as patients receiving high-dose metoclopramide (20-50 mg intravenously) prior to the loading dose of N-acetylcysteine. Controls were patients receiving standard-dose (<20 mg intravenously) metoclopramide prior to loading dose of N-acetylcysteine. Outcome was vomiting within 60 minutes of N-acetylcysteine administration. Results: Twelve of 19 patients (63%) receiving standard-dose metoclopramide vomited N-acetylcysteine. Only 5 of 23 patients (22%) receiving high-dose metoclopramide vomited N-acetylcysteine (crude odds ratio: 6.2; 95% CI [1.3- 30.3]). After controlling for confounding in the logistic regression model, the effect of high-dose metoclopramide in preventing vomiting of N-acetyl cysteine remained significant (adjusted odds ratio: 17.0; 95% CI [2.6- 110.0]). Conclusion: This study supports the efficacy of high-dose metoclopramide to prevent emesis after the oral loading dose of N- acetylcysteine.