[Effects of non-depolarizing muscle relaxants on the duration of mivacurium]

The interaction between Mivacurium and several muscle relaxants results in a slow recovery. We have previously described that small doses of d-tubocurarine prolong the duration of two successful administrations of Mivacurium. The present investigation was designed to uncover if such an effect could be observed after other neuro-muscular blocking drugs were administered, and if so, its consistency during the different methods of their use. Patients (n = 224) were anesthetized with Enflurane and randomly assigned to two control groups which received 100 micrograms/Kg-1 Mivacurium as a bolus or primed. Other groups received: Rocuronium (60 micrograms/Kg-1), Vecuronium (10 micrograms/Kg-1), Atracurium (60 micrograms/Kg-1), d-tubocurarine (50 micrograms/Kg-1) or Pancuronium (8 micrograms/Kg-1) before, after or as a mixture with 90 micrograms/Kg-1 of Mivacurium. The clinical effect was monitored by electromyography and the results show that all these agents prolong the duration of Mivacurium, the last three in a statistically significant fashion independently of the mode of administration. Current hypothesis are reviewed, but no definitive clues are obtained to explain the present results. Our conclusions must be considered as further research on the interaction between non-depolarizing muscle relaxants and a base for new theories on interactions.