[Diltiazem potentiates the neuromuscular blockade by vecuronium in humans]

We investigated interaction of diltiazem with vecuronium using constant infusion technique in 24 ASA class I or II elective surgical patients with no preoperative administration of Ca antagonists. Neuromuscular blockade was evaluated with accelerometry, which measured single twitch height of adductor pollicis muscle. After tracheal intubation under isoflurane anesthesia, patients received either no diltiazem (control group, n = 8)m, 5 mg (bolus) + 2 mcg.kg-1.min-1 constant infusion (2 mcg group, n = 8) or 5 mg (bolus) + 4 mcg.kg-1.min-1 constant infusion (4 mcg group, n = 8). When single twitch height returned to 10% of control value, infusion of vecuronium was started and the infusion rate was adjusted to maintain twitch height at 10% of the control value. After 30 minutes of stable twitch height, the vecuronium infusion rate and plasma diltiazem concentrations were measured. Diltiazem infusion of 4 mcg.kg-1.min-1 decreased the vecuronium infusion rate by 45% compared with 2 other groups. Plasma diltiazem concentrations in patients receiving 4 mcg.kg-1.min-1 were significantly higher than those receiving 2 mcg.kg-1.min-1. In conclusion diltiazem 4 mcg.kg-1.min-1 potentiates the neuromuscular blockade of vecuronium and it relates with the plasma diltiazem concentration.