Comparative haemodynamic effects of tubocurarine and metocurine in the dog

On accout of its histamine releasing and ganglion blocking properties tubocurarine is known to have significant haemodynamic effects. Methylation of the compound produces metocurine and should decrease both histamine release and ganglionic blockade. The haemodynamic effects of these two compounds were compared in 10 mongrel dogs anaesthetized with chloralose and morphine. Haemodynamic measurements were made 2 min before and 2, 5, 10 and 20 min after administration of the drugs. Each animal received three doses of each drug with a 2-h rest period between doses: tubocurarine 0.35 (muscle twitch ED95), 0.7 and 1.4 mg kg-1 and metocurine 0.2 (2 x ED95), 0.4 and 0.8 mg kg-1. All doses of tubocurarine produced an increase in heart rate (212, 197 and 212% of control respectively). The mean arterial pressure decreased significantly with 0.7 mg kg-1 (48% of control; P less than 0.05). Metocurine produced no significant haemodynamic effects except for the largest dose (8 x ED95). The data suggest that the haemodynamic margin of safety with metocurine in the dog is eight times that of tubocurarine.