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

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Abstract
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.