The effect of CO2-induced acid-base changes on the potencies of muscle relaxants and antagonism of neuromuscular block by neostigmine in rat in vitro.

We investigated the influence of CO 2 -induced acid-base changes on the potencies of the monoquaternary relaxants (rocuronium, vecuronium, and d-tubocurarine) and bisquaternary relaxants (pancuronium, pipecuronium, and metocurine), and on the antagonism of their neuromuscular block by neostigmine. Phrenic nerve-hemidiaphragm preparations of rats were used. The pH changes were induced by changing the CO 2 concentration aerating the modified Krebs solution. The potencies of the monoquaternary relaxants increased at 9% CO 2 (pH 7.2) and decreased at 2.5% CO 2 (pH 7.6) from those of 5% CO 2 (pH 7.4) both with and without neostigmine (P<0.05), whereas the potencies of the bisquaternary drugs did not change significantly at different pH levels from control (pH 7.4) both with and without neostigmine