Mivacurium: Dose‐Response Relationship and Administration by Repeated Injection or Infusion

The dose-response relationship and neuromuscular blockade after infusion or repeated injection of mivacurium were studied in 65 patients in nitrous oxide-narcotic anesthesia. The ED95 (twitch tension) was determined in 45 patients by intravenous injection of a single bolus of 30, 39, 47, 54, or 60 μg/kg (9 patients per dose). Another 20 patients received an initial bolus of 2 × ED95 followed either by an infusion started at 5% twitch recovery (i.e., 95% depression) and adjusted to sustain 95% twitch depression (n = 10) or by repeated injection of 0.6 × ED95 whenever twitch tension had recovered to 25% of control (n = 10). Five patients in each of these two groups received 7 μg/kg of neostigmine at 25% twitch recovery, and the others recovered twitch tension spontaneously. The mean ED95 was 73 μg/kg. A 2 × ED95 bolus was followed by complete twitch depression within 2.2 ± 0.7 min. The mean infusion rate resulted in 6 ± 2 μg · kg−1 ± min−1. The ensuing recovery index was 6 ± 3 min. A 6 ± 2 min recovery index was found after up to 10 repeat injections given every 9 ± 3 min. There was no significant effect of neostigmine in both groups. In conclusion, the recovery indices after the infusion or repeat injection of near-equal doses of mivacurium were identical.