S46 During the last ten years, five new intermediate-acting neuromuscular blocking agents have been introduced into pediatric anesthesia. Each of these drugs has unique indications for specific clinical situations, but for most anesthetics these muscle relaxants are interchangeable, cost becoming an important concern. The purpose of this investigation was to compare the costs of these agents when used during surgery of intermediate duration. METHODS: With Ethics Committee approval and parental consent, we studied 96 healthy children 2-10 yr and undergoing elective dental restorations. Premedication was 0.5 mg/kg midazolam p.o. After induction of anesthesia with propofol 3.5 mg/kg, patients randomly received a 2 x ED95 dose of the study drug in a double-blind fashion. The initial dose was either atracurium 480 [micro sign]g/kg, cisatracurium 120 [micro sign]g/kg, mivacurium 240 [micro sign]g/kg, rocuronium 720 [micro sign]g/kg, or vecuronium 100 [micro sign]g/kg. Maintenance of anesthesia was with N2 O 70% and propofol (initial infusion @ 10 mg/kg/hr). Neuromuscular blockade was assessed with TOF-Guard (INMT) acceleration transducer. Infusion of the study drug was begun when T1 of the train-of-four reached 10% of baseline twitch height. The infusion rate of the study drug was adjusted every 2 min, if indicated, to maintain T1 height at 5-15% of baseline. The sample size was chosen to obtain a standard error of the mean which was less than 5% of the mean after 45 minutes of study drug use. Data was analyzed with one-way ANOVA. RESULTS: The groups had similar demographic data. The infusion of the study drug was begun at similar times (approximately 28 min after the bolus), except the mivacurium group which started on average 10 min after the bolus, P<0.001. At current costs, cisatracurium was the least expensive (P<0.001). Vecuronium was initially the most expensive agent and by 45 min mivacurium was the most expensive. (Table 1 and Table 2)Table 1: DRUG USED IN [micro sign]g/kg OF PATIENT WEIGHTTable 2: COST IN $ OF DRUG USED PER KG OF PATIENT WEIGHTDISCUSSION: When a specific intermediate-acting neuromuscular blocking agent is not indicated, cisatracurium is presently the least expensive agent.