Potency and maintenance requirement of atracurium and vecuronium given alone or together

A synergism exists between some competitive muscle relaxants. However, maintenance requirement of a combination of muscle relaxants has been evaluated only in paediatric patients. We studied 45 elective adult surgical patients (ASA I-II) during propofol-alfentanyl-N₂O-O₂-anaesthesia. The first 30 patients were randomized to receive either atracurium or vecuronium to create individual dose-response curves for these muscle relaxants. ED₉₅-values for atracurium and vecuronium were 260±9 and 59±3 μg · kg^-1, respectively (mean±s.e.mean). Requirements of atracurium and vecuronium to maintain an 85–95% neuromuscular blockade were 301 and 83 μg kg^-1 h^-1, respectively. An additional 15 patients received a combination of atracurium and vecuronium (cAV) in an equipotent dose ratio. An ED₉₅ of a cAV was 94± 7 μg · kg^-1 of atracurium together with 21±2 μg · kg^-1 of vecuronium, or 72±6% of one ED₉₅ dose of a parent agent. Potentiation was significant ( P =0.0001). A maintenance requirement of a cAV was 120 μg kg^-1 h^-1 of atracurium together with 27 μg kg^-1 h^-1 of vecuronium. Thus, a significant potentiation was maintained also during the course of anaesthesia. A cAV had an effect like one intermediate-acting agent. If a cAV is used instead of using atracurium or vecuronium alone, the maximal reduction of drug consumption would be approximately 30%.