Pharmacology for Anaesthesia and Intensive Care

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11 Muscle relaxants and anticholinesterases

Rocuronium

This aminosteroidal drug was developed from vecuronium and is structurally differ-

ent at only four positions. Its main advantage is its rapid onset (intubating conditions

within 60–90 seconds), which in turn is due to its low potency.

Amuscle relaxant with a low potency must be given at a higher dose to achieve

aclinically significant effect. A higher number of molecules result in a greater con-

centration gradient from the plasma to the NMJ so that diffusion is faster and onset

time is reduced.

Presentation and uses

Rocuronium is prepared as a colourless solution containing 50 mg in 5 ml. At

0.6 mg.kg−^1 intubating conditions are reached within 100–120 seconds, although

this may be reduced to 60 seconds with higher doses (0.9–1.2 mg.kg−^1 ). Its duration

of action is similar to that of vecuronium.

Other effects


Cardiovascular – like vecuronium it has minimal cardiovascular effects, although

at high doses when used to facilitate a more rapid tracheal intubation, it may cause

an increase in heart rate.

Kinetics

Rocuronium is mainly excreted unchanged in the bile and to a lesser extent in the

urine, although some de-acetylated metabolites may be produced. Its duration of

action may be prolonged in hepatic and renal failure.

Pancuronium

Pancuronium is a bisquaternary aminosteroidal compound.

Presentation and uses

Pancuronium is presented as a colourless solution containing 4 mg in 2 ml and

should be stored at 4◦C. At 0.1 mg.kg−^1 intubating conditions are reached within

90–150 seconds. Its duration of action is about 45 minutes.

Other effects


Cardiovascular – pancuronium causes a tachycardia by blocking cardiac mus-

carinic receptors. It may also have indirect sympathomimetic actions by preventing

the uptake of noradrenaline at post-ganglionic nerve endings.

Kinetics

Between 10% and 40% is plasma protein bound, and in keeping with other drugs in

its class pancuronium has a low volume of distribution. About 35% is metabolized in