Doxacurium Chloride for Neuromuscular Blockade before Tracheal Intubation and Surgery during Nitrous Oxide‐Oxygen‐Narcotic‐Enflurane Anesthesia

The neuromuscular effects of doxacurium (BW A938W were studied in 36 patients, divided into four groups of 9 patients each, given doxacurium either 50 fig/kg (2 × ED95) 5 or 4 minutes or 80 μg/kg (3 × ED95) 4 or 3 minutes before tracheal intubation. Adequate neuromuscular relaxation permitted successful intubation at 5 minutes for doxacurium 50 μg/kg and at 4 minutes for 80 μg/kg. Time to 90% blockade was 5.4 ± 1.5 minutes for doxacurium 50 μg/kg and 3.5 ± 1.2 minutes for 80 μg/kg. Time to 25% spontaneous recovery was 84.7 ± 54.3 minutes for doxacurium 50 μg/kg and 164.4 ± 85.2 minutes for 80 μg/ kg. Either neostigmine 45 tiglkg, neostigmine 60 μg/kg, or edrophonium 1000 μg/kg was given for reversal when T1 had spontaneously recovered to 25% of baseline level, T1 being the first response to repetitive train-of-four (TOF) stimuli (2 Hz for 2 seconds at 10-second intervals) expressed as percent of baseline level. The T4:T1 ratio is the amplitude of the fourth twitch relative to the first twitch in a TOF stimulus expressed as a ratio. Tl rapidly achieved 90% of baseline in 5–10 minutes after reversal of neuromuscular blockade. In contrast, the T4:T1 ratio lagged, recovering to a mean of 0.6 at 20 minutes when T1 was over 90% of baseline. Recovery patterns were not statistically significantly different (unpaired t-test) among the three reversal regimens. Therefore, the reversal data were pooled. No clinically significant hemodynamic effects occurred in any group. The authors conclude that doxacurium is a long-acting muscle relaxant that provides excellent intubating conditions within 5 minutes with 50 uglkg and within 4 minutes with 80 fig/kg. Neuromuscular blockade lasts approximately 85 and 164 minutes, respectively. The neuromuscular blockade is pharmacologically readily reversible.