Betamethasone-induced resistance to neuromuscular blockade: a comparison of atracurium and vecuronium in vitro.

Steroids induce resistance to neuromuscular blocking drugs. Betamethasone-induced resistance to vecuronium has been demonstrated in vitro, and a presynaptic site of interaction has been suggested. This study investigated whether atracurium is similarly affected. Rat phrenic nerve-hemidiaphragm preparations were bathed in a physiologic solution, and one-half were exposed to betamethasone (1 mumol/L). Dose responses were recorded for atracurium (8-13 mumol/L) and vecuronium (2-12 mumol/L) for control and betamethasone-treated preparations. In comparison to control, the betamethasone groups had significantly less depression of muscle contraction force at all concentrations of atracurium (P = 0.0004) and vecuronium (P = 0.002). The calculated ED50 (50% depression of muscle contraction force, expressed as mean +/- SEM) for atracurium was 8.83 +/- 0.62 mumol/L for controls and 11.19 +/- 0.54 mumol/L for betamethasone-treated preparations. The calculated ED50 for vecuronium was 4.72 +/- 0.41 mumol/L for controls and 6.84 +/- 0.66 mumol/L for betamethasone-treated preparations. Betamethasone therefore increased the ED50 for atracurium by 27% and vecuronium by 45%; however, the magnitudes of these differences were not significant (P = 0.74) between the neuromuscular blocking agents. These results indicate that betamethasone-induced resistance to nondepolarizing neuromuscular blockade affects both atracurium and vecuronium to similar degrees in vitro.