(1) Curare. Curare is used to produce a complete skeletal muscle
relaxation or flaccid paralysis of skeletal muscle during general anesthesia and other
procedures. It is a potentially dangerous drug for obvious reasons: Too much of a drug
administered too quickly can result in paralysis of the muscles that control respiration.
The primary side effects associated with curare are bradycardia and hypotension. The
individual responsible for administering the curare during anesthesia must monitor the
vital signs of the patient to ensure that the patient does not experience toxic effects from
the curare. That person will also have to ensure that the patient is able to breathe
(sometimes mechanical assistance is required) when curare is administered since
curare relaxes all the skeletal muscles of the body, and the patient sometimes finds
difficulty in breathing. Curare is supplied in an injectable form.
(2) Pancuronium (Pavulon). Pancuronium is five times more potent than
curare and it produces complete skeletal muscle relaxation. It poses the same risk
factors for the patient, as does curare. The primary side effects seen with pancuronium
are cardiac arrhythmias of various types.
b. The depolarizing blocking agents act like an excess of acetylcholine to
depolarize the muscle receptor site and prevent its repolarization. Thus, there is an
initial depolarization at the neuromuscular junction producing muscle contraction; but
since the muscle receptor site cannot depolarize, complete skeletal muscle relaxation
follows. In general, the relaxation effects produced by the depolarizing agents are of
shorter duration than the relaxation produced by the non-depolarizing agents.
(1) Succinylcholine (Anectine). Succinylcholine is a depolarizing agent
used to produce complete muscle relaxation for various surgical procedures. The
primary side effects associated with succinylcholine are cardiac arrhythmias and post-
operative apnea (temporary stoppage of breathing).
(2) Decamethonium bromide (Syncurine). Decamethonium bromide is
used as a muscle relaxant for relatively short surgical procedures. Side effects
associated with this agent include muscle soreness, respiratory depression, and
Section III. CENTRALLY ACTING SKELETAL MUSCLE RELAXANTS
Centrally acting skeletal muscle relaxants are so called because they act on the
central nervous system to decrease muscle tone. They decrease muscle tone by
depressing the internuncial neurons at the spinal cord (Figures 3-2 and 3-3). When
given in normal therapeutic doses, these agents are not potent enough to produce
flaccid paralysis. However, large oral or injectable doses of these drugs may produce
hypotension, flaccid paralysis, and respiratory depression. Many of these drugs are
similar in chemical structure to antianxiety agents. These agents are used to relieve
skeletal muscle spasms. Whether relief of pain achieved by patients taking these drugs
is due to their muscle relaxant effect or to their sedative effect is unknown.