A prospective analysis of intramuscular meperidine, promethazine, and chlorpromazine in pediatric emergency department patients. STUDY OBJECTIVE: To examine physiologic responses and efficacy of 2, 1, and 1 mg/kg IM meperidine, promethazine, and chlorpromazine (MPC), respectively, in children. DESIGN: Prospective, unblinded trial. SETTING: A university and community emergency department. PATIENTS: Sixty-three hemodynamically and neurologically stable children. INTERVENTION: Single dose of IM MPC. MEASUREMENTS AND MAIN RESULTS: Serial respirations, heart rate, arterial systolic blood pressure, oxygen saturation, and Glasgow Coma Scale were measured at 30-minute intervals. Effectiveness was assessed by two independent observers using separate visual analog scales for cooperation and sedation. Times to sleep (27 +/- 24 minutes), sitting upright (103 +/- 87 minutes), ED discharge (4.7 +/- 2.4 hours), eating (11 +/- 7.9 hours), and normal behavior (19 +/- 15 hours) were acceptable. Minor, but statistically significant, changes in respiration rate (-1.9 +/- 0.4), heart rate (+4.5 +/- 1.8), oxygen saturation (-0.7 +/- 0.3%), and Glasgow Coma Scale (-2.5 +/- 0.6) occurred for 120 minutes after MPC. No serious complications or resuscitation were required. Mean visual analog scale scores were 5.0/10.4 or more in 71% of cases, with interobserver agreement very good (cooperation, r = .79; effectiveness, r = .80). Twenty-nine percent of children were judged insufficiently sedated. CONCLUSION: IM MPC is a safe and generally effective agent for ED procedures in selected children. 