The Effect of a Subthreshold Dose of d‐Tubocurarine on the Neuromuscular Blocking Action of Succinylcholine in Anesthetized Man

Dose‐response curves of succinylcholine (SuCh) were obtained in anesthetized patients by means of mechanograms of the flexion‐grip response of the hand to ulnar nerve stimulation. A subparalyzing dose (0.04 mg/kg b.w.) of d‐tubocurarine (d‐TC) administered prior to SuCh (0.025–1.6 mg/kg b.w.) exhibited a shift of the dose‐response curves toward the right, i.e., a diminishing effect on magnitude and duration of the SuCh induced neuromuscular blockade. The effective dose of SuCh required to produce a half‐maximal inhibition of the contractile force (ED50, 0.12 mg/kg before d‐TC) was increased to 0.3 mg/kg (15 min after d‐TC), 0.26 mg/kg (after 30 min), and 0.23 mg/kg (after 45 min). Thus, d‐TC pretreatment employed under clinical conditions to prevent potential hazards of SuCh requires a significant larger dose of SuCh to ensure consistently adequate relaxation.