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 micrograms.kg-1, respectively (mean +/- s.e. mean). Requirements of atracurium and vecuronium to maintain an 85-95% neuromuscular blockade were 301 and 83 micrograms 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 micrograms.kg-1 of atracurium together with 21 +/- 2 micrograms.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 micrograms kg-1 h-1 of atracurium together with 27 micrograms 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%.